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Icpr4 2d Manual

This document is a user's manual and technical reference for overland flow concepts and theory, detailing the modeling approach used in ICPR. It covers the basic concepts, equations of flow, and the automated mesh generation process for simulating 2D overland flow. Key components include mass balance equations, momentum equations, and the use of triangular and honeycomb meshes for effective water flow modeling.

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0% found this document useful (0 votes)

653 views276 pages

Icpr4 2d Manual

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thomas82896

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User’s Manual and Technical Reference

Volume 2, Chapter 19
Overland Flow, Concepts and Theory

September 2017

© 2017, All Rights Reserved

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
19. Overland Flow, Concepts and Theory

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19-2 ICPR4 User’s Manual and Technical Reference, Volume 2

Contents
19. Overland Flow, Concepts and Theory ......................................................................................... 5
19.1 Basic Concepts ...................................................................................................................... 5
19.2 Equations of Flow .................................................................................................................. 9
19.2.1 Mass Balance Equation ................................................................................................... 9
19.2.2 Momentum Equation.................................................................................................... 11
19.2.3 Energy Equation ........................................................................................................... 11
19.2.4 Diffusive Wave Equation............................................................................................... 12
19.2.5 Manning’s n for Overland Flow ..................................................................................... 12
19.2.6 Damping Threshold ...................................................................................................... 13
19.2.7 Area Reduction Factor .................................................................................................. 13
19.2.8 Edge Length and Slope ................................................................................................. 14
19.3 Time Marching Algorithms .................................................................................................. 15

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19-4 ICPR4 User’s Manual and Technical Reference, Volume 2

19. Overland Flow, Concepts and Theory

Examples of 1D channel flow and 2D overland flow are shown in the photographs below. While open
channel flow, including pipe flow, typically has a well-defined flow direction, overland flow does not.
Water can move in many directions and flow patterns can change during a storm event. If overland
flow patterns and velocities are of concern, then a two-dimensional approach may be warranted.
This chapter describes the basic concepts and theory of 2D overland flow in ICPR.

1D Channel Flow 2D Overland Flow

19.1 Basic Concepts

ICPR uses a flexible triangular computational
mesh for 2D overland flow. The mesh
generation is automated and relies on various
graphical mapping features. The vertices of
the triangles are treated as nodes in the
model and the sides of triangles become
overland flow links.

Control volumes are formed around the

vertices and extend to the midpoints of the
triangle sides and to the geometric center of

the triangle (i.e. the centroid) as shown above.

This is considered a finite volume approach and

uses two meshes. The momentum equations (and
energy and diffusive wave equations) are lumped
along the edges of the triangular mesh and the
mass balance equations are lumped at the control
volumes (irregular polygons) formed around the
vertices of the triangles. This collection of irregular

ICPR4 User’s Manual and Technical Reference, Volume 2 19-5

polygons is referred to as the honeycomb mesh, or simply, the honeycomb.

Water is moved from honeycomb to honeycomb along the sides of the triangles. Diamonds are
formed along the triangle sides and extend from the connecting vertices and the adjacent triangle
centroids as shown below. The diamonds are idealized into equivalent rectangles with averaged 2D
ground slopes.

Recall the three primary building blocks of

ICPR: nodes, links, and basins. In the 2D
overland flow regime, the triangle vertices
are the nodes, the triangle sides are the
links, and the individual honeycombs are
the basins (i.e. catchment areas).

Manual construction of a triangular mesh

would be impractical for all but the
simplest of models. Therefore, ICPR fully
automates mesh generation and
parameterization of the mesh, and it does
this using a variety of geo-referenced layers
including “surfaces”, “maps” and “features”.

The triangular mesh is constructed first and then the honeycomb and diamond meshes are derived
from the triangles. A quick overview of the mesh creation process and parameterization are
discussed in this section.

A 2D overland flow “region” must be created first in the form

of a closed polygon that defines the limits of the area to be
modeled. This can be drawn inside ICPR, or a polygon can be
imported as either a shapefile or a DXF file. An example of an
overland flow region is shown to the left superimposed with a
digital elevation model (DEM). The square grid (50-ft x 50-ft
cells) is provided for referencing purposes only.

Once the region is created, “map features” are added to

characterize the terrain, handle boundary conditions and
interface with the one-dimensional components. A list of the various overland flow map features is
shown below.

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“Breakpoints” are frequently used to characterize

the terrain. Triangle vertices are guaranteed at
breakpoint locations. Without going into all the
details at this point, a pattern of breakpoints has
been added to the overland flow region such that
triangle sides have a length of 50 feet. A condition
was also specified such that no breakpoint be
placed within 50 feet of the region boundary. These
are options, not requirements. The resulting set of
breakpoints is shown below.

In an effort to keep this example simple, no other

map features are used. The resulting triangular
mesh is shown below on the right. Notice the regular
triangle pattern away from the region boundary, but triangles grow and shrink as needed near the
region boundary. This is the flexible nature of triangular meshes. ICPR uses the Delaunay method of
triangulation.

In addition to generating the triangular mesh, ICPR also

automatically places arrow heads along the triangle sides
indicating the down gradient direction as shown to the left.
The down gradient direction is determined by
superimposing the mesh with a ground surface DEM. ICPR
sets elevations at every vertex in the mesh based on the
DEM ground elevations at the vertex location. These
become invert elevations for the overland flow links formed
along the sides of the triangles. Consequently, a DEM
representing the ground elevation must be included in the
model data set.

ICPR4 User’s Manual and Technical Reference, Volume 2 19-7

The honeycomb is formed around the triangle vertices as previously described and shown below.
Each honeycomb is treated as a drainage basin. The honeycomb is intersected with various polygon

mapping layers such as a soil zone map layer and a land cover zone map layer as shown above and to
the right. Sub-polygons (referred to as “basin polygons”) within each honeycomb are formed by this
intersection and a water balance is performed on each of them accounting for rainfall, surface
ponding, infiltration, evapotranspiration and applied irrigation. Once the losses are accounted for,
any remaining water is “rainfall excess”. The rainfall excess for all basin polygons within a given
honeycomb are summed and then applied directly to the 2D node located at the vertex of a triangle.
The hydraulics then move the rainfall excess from node to node.

Diamonds are intersected with a polygon map layer of “roughness zones”. These roughness zones
are used in conjunction with a roughness zone lookup table for setting Manning’s n, dampening
thresholds and area reduction factors. Area weighted values of each of these parameters are set at
runtime.

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To summarize:

1. ICPR constructs the triangular mesh from various graphical map features.
2. Nodes are placed at the vertices.
3. The honeycomb and diamond meshes are derived from the triangular mesh.
4. Basins (catchment areas) are formed by the honeycombs.
5. Links connect nodes along the sides of the triangles and are idealized as equivalent
rectangles and average 2D slopes are calculated for the diamond.
6. Ground elevations and initial water elevations at the nodes are extracted from DEMs.
7. The diamond mesh is intersected with a roughness zone map layer to determine area-
weighted Manning’s n, dampening threshold and area reduction factor.
8. The honeycomb mesh is intersected with various map layers (e.g., soil, land cover, rainfall
zones) to form basin polygons, each with its own set of infiltration and impervious
characteristics.

19.2 Equations of Flow

ICPR uses a finite volume approach for 2D overland flow modeling as already mentioned. Control
volumes in the form of irregular shaped polygons (honeycombs) are created around vertices.
Connections (links) are formed between control volumes and water is moved from one control
volume to the next via these links. ICPR forms links with all adjacent cells, but the number of adjacent
cells is variable. In the first honeycomb shown below, there are 6 adjacent cells, while the second
honeycomb has 8 adjacent cells. ICPR uses a one-dimensional form of the momentum equation
(with energy and diffusive wave options) and average 2D ground slopes to move water between
control volumes. The various equations of flow used by ICPR are discussed in the following sections.

19.2.1 Mass Balance Equation

The mass balance equation for the control volume of an individual node is written as follows:

  Q  Qout  
dz   in  dt
 A
 surface 

where,

dz incremental change in stage (f, m)

ICPR4 User’s Manual and Technical Reference, Volume 2 19-9

dt computational time step (s)

Qin total inflow rate (f3s-1, m3s-1)

Qout total outflow rate (f3s-1, m3s-1)

Asurface “wet” surface area (f2, m2)

and,

Qin   Qlinkin   Qexcess   Qexternal   Qseepage

Qout   Qlinkout   Qirrigation

Asurface wetted surface area of the control volume (f2, m2)

Q linkin sum of all link flow rates entering control volume (f3s-1, m3s-1)

Q linkout sum of all link flow rates leaving control volume (f3s-1, m3s-1)

Q excess sum of rainfall excess rates for all basin polygons (f 3s-1, m3s-1)

Q external sum of inflows from all external sources (f3s-1, m3s-1)

Q seepage sum of seepage flow from groundwater model (f3s-1, m3s-1)

Q irrigation sum of irrigation water pulled from surface node (f3s-1, m3s-1)

As previously mentioned, an individual honeycomb is a basin or catchment area in ICPR. This basin
is further discretized by intersecting soil and land use polygons with the honeycomb as shown
below. The polygons formed by these intersections are referred to
as basin polygons. As will be discussed subsequently, additional
basin polygons can be formed by intersecting rainfall zone
polygons such as a NEXRAD fishnet or weather station Thiessen
polygons.

As noted above, the term Q excess is the sum of rainfall excess

rates for all basin polygons within an individual honeycomb. It is
the sum of precipitation and applied irrigation minus the sum of
infiltration and evapotranspiration. A separate mass balance accounting is performed for each
basin polygon to determine its rainfall excess amount. When water is ponded on the surface, it is

19-10 ICPR4 User’s Manual and Technical Reference, Volume 2

used to satisfy ET and can also infiltrate into the soil column. Consequently, it is possible to have a
negative rainfall excess value during a simulation.

19.2.2 Momentum Equation

There are three options available for calculating flow along the sides of triangles: (1) momentum
equation; (2) energy equation; and (3) diffusive wave equation. The momentum equation is
discussed in this section followed by the energy and diffusive wave equations.

The following form of the St. Venant equation is used in ICPR to calculate flow along the sides of
triangles (overland flow links). The solution algorithm is like that used in the EPA SWMM model (v5)
for 1D flow, but minor losses have been dropped for overland flow. The momentum equation
includes inertial terms for local and convective acceleration.

Q   Q / A 
2
Z
  gA  gAS f  0
t x x

Solving for Q yields:

Qt  Qgravity  Qinertial
Qt t 
1  Q friction

Qgravity  g A( Z1  Z 2 )t / L

2
Qinertial 2V ( A  At )  V ( A2  A1 ) t / L

gn 2 V t
Q friction  4/3
k2 R

19.2.3 Energy Equation

The energy equation is more robust than the momentum equation in terms of its solution, while
including some of the inertial effects of the momentum equation. It is a reasonable balance between
the full momentum equation and the simpler diffusive wave equation.

V12 V2
Z1   Z2  2  hf
2g 2g

Solving for Q yields:

ICPR4 User’s Manual and Technical Reference, Volume 2 19-11

1/ 2
 
 
 Z1  Z 2 
Q 
 1  1  1   xC 
 2 g  A2 2 A12  f


19.2.4 Diffusive Wave Equation

The diffusive wave equation drops all inertial terms and is the simplest and, in theory, is the fastest
of the three options.

Z1  Z 2  h f

Solving for Q yields:

1/ 2
 Z  Z 2 
Q 1 
 xC f 

19.2.5 Manning’s n for Overland Flow

ICPR uses an exponential decay function for transitioning between a shallow condition n-value and a
deep condition n-value. The shallow n-value begins at the surface and the deep n-value occurs at a
user specified depth range and above. The following function is used for the transition between
shallow and deep flow.

n  nshallowe( k )( d )

 n 
ln  deep 
n
k   shallow 
d max

n Manning’s roughness coefficient at depth d

nshallow Manning’s roughness coefficient at the ground surface

ndeep Manning’s roughness coefficient at depths of 3 feet (0.914 meters) or greater

k exponential decay factor (f-1, m-1)

d depth of flow (f, m)

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d max user specified depth range to ndeep (f, m)

Shallow and deep Manning’s n values are specified by roughness zone in the 2D overland flow
roughness zone lookup tables.

19.2.6 Damping Threshold

A default threshold can be set in the simulation control data for 1D and 2D links. But, unlike 1D links
the damping threshold cannot be set for individual 2D links. Instead, it can be set by roughness zone
in the overland flow roughness zone lookup table. Typically, these are set to zero in the lookup table.
And if so, the default value set in the simulation control data form is used. Non-zero values in the
lookup table override the default value.

When the absolute value of the difference in water levels at both ends of a link fall within the specified
“Damping Threshold”, the calculated flow is reduced in accordance with the equation below:

Q '  fd Q

Where f d is a flow reduction factor determined from a parabolic function of the change in stage and
Q ' is the reduced flow.

This parameter is used to help smooth out instabilities. Typically, when used, values range from
0.0001’ to 0.01’ and rarely should it exceed 0.1’. In general, the stability improves as the threshold
increases and it allows for larger computational time increments than would otherwise be possible.
However, it also increases head losses along the link for which it is used.

19.2.7 Area Reduction Factor

The area reduction factor refers to a reduction in cross sectional area as opposed to surface area. It
is a way to account for lost storage and obstructions in the overland flow plane such as a dense stand
of trees. The width of a link is reduced by multiplying the unadjusted width by the area reduction
factor as follows.

W '  f arf W

The area reduction factor is set by roughness zone, like the damping threshold. If you do not wish to
reduce the width, then set the area reduction factor to 1.0.

ICPR4 User’s Manual and Technical Reference, Volume 2 19-13

19.2.8 Edge Length and Slope

As discussed, water moves along triangle edges for 2D
overland flow and an idealized rectangular shape is
used for the flow computations. The average length,
L, and average width, W, of this idealized rectangle are
derived from the diamond shape area, ADIAMOND, that is
formed along a given triangle edge.

If the “Edge Length Option” in the simulation control

data (Simulation Manager, Tolerances & Options Tab)
is set to “Automatic” (the typical setting), then the
average edge length and the average width are
calculated as follows:

L = (2/3) x LA-B

W = ADIAMOND / L

If the “Edge Length Option” is set to “Manual”, then an “Edge Length Factor” must be set to a decimal
value greater than zero but less than or equal to 1. The resulting edge length and average width are
calculated as follows:

L = FEDGE (LA-B)

W = ADIAMOND / L

where, FEDGE, is the edge length factor.

The manual edge length option and edge length factor can be used to help calibrate a model. As the
edge length factor is increased, the average width decreases and consequently, the overall flow of
water tends to slow down. In effect, attenuation of flows can be achieved by increasing the edge
length factor. This parameter has a similar effect as the peak rate factor for the unit hydrograph
method (the smaller the peak rate factor, the slower the water moves through a drainage basin).
Keep in mind that it is impossible to perfectly account for all the storage and the intricate flow paths
in natural systems with any 2D model. The edge length factor provides a mechanism to somewhat
offset the impact of those inherent inaccuracies related to the model setup.

If the edge length factor is set to 1, the average slope is set to:

S = SA-B = (ZA - ZB) / LA-B

Otherwise, the following 2D average slope is used:

S = [ (SA-B)2 + (S1-2 + S3-4)2 ](1/2)

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19.3 Time Marching Algorithms

There are two different time marching options available in ICPR for the surface hydraulics. Both are
fully integrated with 1D flow computations. In other words, a single system of equations is formed
for 1D and 2D surface flow and solved simultaneously.

2D overland flow in ICPR is fully integrated with 1D

surface hydraulics rather than coupled together.

The Successive Approximation with Over-Relaxation (SAOR) technique, the first time marching
method, employs an iterative solution and has an adaptive time step, meaning that the time step
changes throughout the simulation. However, the time step does not change spatially and a single
time step is used for the entire surface hydraulics portion of the model at a given point in time.
Consequently, the time step is typically driven by the node with the least amount of storage. The
method does lend itself well to parallel processing. Details of the SAOR method are described below
and is like the time marching scheme used in the EPA SWMM model.

The FIREBALL method is the second option for time marching and is a technique that is unique to
ICPR. Time steps vary not only in time, but also spatially. The potential speed gains are enormous
for large 2D models. Although parallel processing does take place with the FIREBALL method, it is
not as efficient as the SAOR method. Also, there is some additional overhead needed to set local
time steps in complex networks. But even with these caveats, the FIREBALL method can be up to 30
times faster than the SAOR method for large projects. Details of the method are described in
Section 17.4.1.2

In general, the SAOR method is more stable than the FIREBALL method. Consequently, tighter
stability criteria are required for the FIREBALL method. Mass balance checks are important with
both methods. Details of these time marching algorithms and specific input parameters for each
method are discussed in Section 17.4.1.

ICPR4 User’s Manual and Technical Reference, Volume 2 19-15

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19-16 ICPR4 User’s Manual and Technical Reference, Volume 2

September 2017

© 2017, All Rights Reserved

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
20. Overland Flow Regions

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20-2 ICPR4 User’s Manual and Technical Reference, Volume 2

Contents
20. Overland Flow Regions............................................................................................................... 5
20.1 Creating an Overland Flow Region ........................................................................................ 5
20.1.1 Create and Draw Region in ICPR ..................................................................................... 5
20.1.2 Importing an Overland Flow Region ............................................................................... 7
20.2 Overland Flow Region Manager ............................................................................................ 9
20.2.1 Roughness Zones (required) ......................................................................................... 13
20.2.2 Soil Zones (required) .................................................................................................... 13
20.2.3 Land Cover Zones (required)......................................................................................... 13
20.2.4 Rainfall Zones (optional) .............................................................................................. 14
20.2.5 Mapped Basin Map Layer (optional) ............................................................................. 15
20.2.6 Infiltration Method Zones (optional) ............................................................................ 16
20.2.7 Reference ET Zones (optional) ...................................................................................... 16
20.2.8 Crop Coefficient Zones (required when ET is included) ..................................................17

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20-4 ICPR4 User’s Manual and Technical Reference, Volume 2

20. Overland Flow Regions

An overland flow region is a closed polygon that encompasses the extents of the area to be modeled.
It is like a watershed boundary and usually follows major drainage divides. A no flow boundary
condition is assumed along the perimeter of the region unless other boundary conditions are
specified.

At least one overland flow region must be created to model 2D overland flow. Mapping features are
placed in the region and are used to construct the computational mesh. Generally, a single region is
used for most 2D projects but multiple regions can be used as a management tool for large complex
projects.

The purpose of this chapter is to describe how to create a region, and once it is created, how to
manage the various layers of information needed to parameterize the computational mesh.

20.1 Creating an Overland Flow Region

There are two primary ways to create an overland flow region. The first is to draw it manually in ICPR
and the second is to import either a shapefile or a DXF file. Regardless of the method used, you must
work in the Graphic View. Also, it is critical to have your spatial coordinate/projection system
established ahead of time. Mesh building and parameterization depend on geo-referencing and all
geo-referenced information must be on the same spatial system at the time of importation. ICPR
has no means of changing spatial projection systems once data has been entered or imported. And,
ICPR cannot work with multiple spatial systems within a given project.

Generally, the Coordinate Reference System (CRS)

should be set for the project prior to creating or
importing an overland flow region boundary.

20.1.1 Create and Draw Region in ICPR

Typically, either a background image or a DEM (or both) are needed as a guide if you are going to
create and manually draw a region in ICPR. To create a region, click the “Create Overland Flow
Region” icon at the top of the graphic view window as shown to
the right. If the autoname feature is turned off, you will be
prompted for a region name. Otherwise, the region will be
automatically named and a prompt will appear at the bottom of
the graphic view window as shown below. You can begin
drawing at this point.

ICPR4 User’s Manual and Technical Reference, Volume 2 20-5

A simple example is shown below where the region boundary is snapped to the reference grid at
several locations. The region polygon is closed by pressing “C” or with a right mouse click. Notice
that the region name (circled in red and designated “OFR-001”) appears on the tool bar located at
the top of the graphic view. This is the “active” region and any other 2D overland flow map features
created are assigned to the active region. A dropdown list of regions is available if more than one
region has been created, allowing you to change the active region.

A tree structure exists on the left side of the general tab that allows you to toggle various graphic
elements on and off as shown below left. Graphic elements associated with overland flow regions
are circled in red. Notice the name “OFR-001” appears directly below “Overland Flow Regions” in the
data tree. The region boundary can be toggled on and off by checking the box next to shape, directly
below “OFR-001”.

There are several ways to delete a region, but you need to be extremely
careful because not only will the region graphic be deleted, but all data
and features assigned to a region will also be deleted. The “Delete
Single” icon shown to the right allows you to pick a specific feature or
graphic element to delete.

20-6 ICPR4 User’s Manual and Technical Reference, Volume 2

If you need to make a change to the region boundary, it is better

to use the “Edit Polyline” icon shown to the right rather than
deleting it first and creating a new one. You can redraw the
entire region boundary with the edit polyline tool without losing
any data associated with the region.

20.1.2 Importing an Overland Flow Region

It is often convenient to import a region boundary that was created in GIS or CAD. This can be done
by right-clicking on “Overland Flow Regions” on the data tree of the general tab as shown below.
You can import either a shapefile, a DXF file or CSV files.

Here are some important things to keep in mind when importing regions from other sources:

1. You should use as few points as possible to define the region boundary without
compromising accuracy. For example, there are ArcHydro tools available with
ArcGIS that automatically delineate watershed boundaries from DEMs. These
routines trace along the edges of the DEM cells and result in thousands of very
short line segments (e.g. 5 feet). When ICPR generates the triangular mesh, a
vertex is placed at every point along the region polygon. If the ArcHydro generated
line work is not simplified, it will quickly make the ICPR overland flow model
unwieldy and computationally inefficient.

ICPR4 User’s Manual and Technical Reference, Volume 2 20-7

2. If you are using ArcGIS generated shapefiles, make sure you are exporting the file
with a consistent projection system if you haven’t defined a CRS for the ICPR
project. If you have defined a CRS, then ICPR will utilize the projection file that
accompanies the shapefile to translate it into the ICPR CRS.
3. The shapefile should be a polygon type and accompanied by a dbf file with a name
field. Also, you should explode multi-part features.
4. For DXF files, use the AutoCAD R12 format. You will need to know the layer names
for line work and text. ICPR can import only lines, arcs and closed polylines for
polygons. Make sure that the region boundary is a closed polygon – i.e. snap the
ends. DXF files do not have projection files, so you must ensure that the spatial data
is consistent with the CRS used in your ICPR project.

You can view the imported region boundary by first toggling off
the grid and then clicking the zoom extents icon as shown to
the right. This is equivalent to zooming to the extents of visible
entities. The color of the boundary and line width can be
adjusted using the “Graphic Element Properties Manager” as shown below. Also, shown below is
an imported region boundary.

20-8 ICPR4 User’s Manual and Technical Reference, Volume 2

20.2 Overland Flow Region Manager

As described previously in this chapter, automated parameterization depends on the DEMs and on
polygon zones in the form of map layers. The overland flow
region manager is used to assign the various map layers and
DEMs needed for final parameterization to the region. The
overland flow region manager form is shown on the
following page.

One of the first things you might notice about the overland flow region manager is that you cannot
create a new region inside the manager. Regions can only be created graphically in ICPR in the
graphic view form or by importing a region boundary from a shape file or a DXF file. You can,
however, delete a region by clicking the delete button at the bottom of the form. Once again, if you

ICPR4 User’s Manual and Technical Reference, Volume 2 20-9

delete a region, you will simultaneously delete all data associated with it. So be very careful with the
delete button. The name of the region can be changed in the region manager, but the scenario
cannot be changed.

The minimum triangulation angle affects the shape and number of triangles. In general, as the angle
increases, so do the number of triangles. We have found a minimum angle of about 21 degrees to be
optimal in terms of number of triangles. But, 45 degrees generally produces better shaped triangles,
although many more of them. For example, the triangular meshes for 21- and 45-degree minimum
angles are shown below and generate 241 and 422 triangles, respectively.

21-Degree Minimum Angle 45-Degree Minimum Angle

ICPR goes through a triangle refinement process using the Delaunay method of triangulation to meet
the minimum angle constraint. Situations can occur where thousands of tiny triangles are created to
satisfy the minimum angle criteria. Consequently, a second constraint is used to stop the refinement
process. If, during the refinement process, a triangle area drops below a specified minimum
triangulation area, then the refinement process stops. A minimum triangulation area of about 150
square feet (14 square meters) works well in most cases.

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ICPR4 User’s Manual and Technical Reference, Volume 2 20-11

Preliminary triangle and honeycomb meshes can be

constructed by clicking the “Preprocess” button at the
lower-left corner of the region manager form. This is
useful for evaluating triangle densities based on map
features prior to final mesh construction or simulation
execution.

A tool is available to help in your evaluation of the

preliminary triangular mesh. Click the “Search” tab
located at the bottom left corner on the Graphic View.
The “Triangular Layer Mesh Links” is located at the
bottom of the “Search” tab. You can search for triangle sides less than or equal to a specified
maximum by using the “Search Tab” in the Graphic View. The example shown to the left has found
15 triangles sides less than or equal to 12
feet, with the shortest being 10.22 feet.
The offending triangle side appears in the
center of the graphic view editor. You can
decide at this point whether to change a
2D feature such that the “short” triangle
side is eliminated. For example, if you
happen to have a breakpoint very close to
a breakline, you might want to delete the
breakpoint.

The “Search” tab also allows you to locate

specific 2D overland flow and 2D
groundwater features as well as 1D nodes and links, by name.

After the diamond and honeycomb meshes have been created (using the Scenario Build), they are
rasterized for subsequent polygon processing with other mapping layers. The cell size data fields
establish the pixel size for this rasterization process. In general, these should be relatively small
numbers such as 1 foot as shown in the region manager on the previous page. But larger cell sizes
might be needed for larger projects due to memory issues. Just keep in mind that these cell sizes
must be even multiples of polygon map layer cell sizes. For example, if the cell size for a land cover
polygon map layer is set to 4 feet, then the diamond and honeycomb cell sizes would have to be
either 0.25, 0.50, 1, 2 or 4. Diamond and honeycomb cell sizes should be less than or equal to other
map layer cell sizes.

There are 2 surfaces (DEMs) that need to be set in the region manager: (1) the ground surface; and,
(2) the initial stage surface. If the overland flow plane is expected to be dry at the onset of the
simulation, then the ground surface DEM can be used for the initial stage surface. Otherwise a
separate DEM is required.

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It is possible to use a single elevation for either the ground surface or initial stage surface by checking
the appropriate box and typing in an elevation. This is convenient for testing hypothetical situations
or specific features of the program, but is rarely used for actual conditions.

The following sections describe the various map layer types that are used for 2D overland flow
modeling. Note that you can right click in most of the data fields to select from a list of available map
layers.

20.2.1 Roughness Zones (required)

Purpose: Intersects the diamond mesh and is used in conjunction with a “roughness set” lookup table
to set area weighted Manning’s n, dampening thresholds and area reduction factors for overland flow
links along the sides of triangles.

It is possible to use a single

roughness zone by checking the
box as shown above and typing the name of the zone to be included
in the model. In this example, the zone “Pasture” must be included
in the roughness lookup table.

Corresponding Lookup Table: Roughness Sets (see Section 7.2)

20.2.2 Soil Zones (required)

Purpose: Intersects honeycomb mesh and mapped basin layer (if present) and is used in conjunction
with “rainfall excess methods” lookup tables. Infiltration parameters for pervious areas are
established.

It is possible to use a single soil

zone by checking the box as
shown above and typing the name of the zone to be included in the model. In this example, the
zone “Myakka Fine Sand” must be included in the appropriate rainfall excess method lookup table.

Corresponding Lookup Table(s):

Green-Ampt Sets, Vertical Layers Sets,
Curve Number Sets. (see Sections 7.4,
7.5 and 7.6, respectively)

20.2.3 Land Cover Zones (required)

Purpose: Intersects honeycomb mesh
and mapped basin layer (if present) and
is used in conjunction with “impervious
sets” lookup table. Total impervious percentages, DCIA percentages and initial abstraction
amounts are set. If the curve number method is being used for infiltration, then the “curve number
sets” lookup table is also used.

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It is possible to use a single land

cover zone by checking the box as
shown above and typing the name of the zone to be included
in the model. In this example, the zone “SFR” must be
included in the appropriate impervious lookup table.

Corresponding Lookup Table(s): Impervious Sets (and Curve

Number Sets if curve number option in play). (see Section 7.7
for impervious sets)

20.2.4 Rainfall Zones (optional)

Purpose: Intersects honeycomb mesh and mapped
basin layer (if present) and is used in conjunction with
“Resources > Rainfall” folder. Rainfall data can be
varied both spatially and temporally with this option.
In the example shown to the right, a NEXRAD
“fishnet” was imported as a map layer and
superimposed with the region boundary. Each “pixel”
(zone) is approximately 2km on each side. A text file
is created for each pixel and includes a time history of
rainfall. The files are placed in the resources folder as
shown below. (see Section 6.1 for rainfall file
specifications)

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It is possible to use a single rainfall

zone by checking the box as shown
above and typing the name of the zone to be used throughout the overland flow region. A text file
must be placed in the resource folder with the appropriate data.

20.2.5 Mapped Basin Map Layer (optional)

Purpose: Used to integrate traditional hydrology (e.g., NRCS unit hydrographs, SBUH) with 2D
overland flow. For example, an urbanized area is depicted below inside an overland flow region
boundary. Traditional hydrology is proposed for the urbanized area and 2D overland flow is proposed
beyond it. Mapped basins are used within an overland flow region for this purpose. Notice how the
triangular mesh is generated around the proposed mapped basin area. Mapped basins are also used
to integrate traditional hydrology with 2D groundwater flow.

It is possible to use a single

mapped basin by checking the box
as shown to the left and typing the name of the basin to be included in the model.

Mapped Basin data forms must be completed for each of the basins
as shown below. The mapped basin layer is intersected with other
map layers such as soil zones, land cover zones and rainfall zones.

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20.2.6 Infiltration Method Zones (optional)

Purpose: Intersects honeycomb mesh and mapped basin layer (if present) and is used to spatially
vary the rainfall excess (infiltration) method. This layer only sets the method type and does not
interact with a lookup table directly. The polygon zones must be identified with the letters “G”, “V”,
and “C” for the Green-Ampt method, vertical layers, and the curve number method, respectively.

In most cases, a single infiltration method is used throughout a given region. To implement a single
method, check the box as shown below and select the method you propose to use.

20.2.7 Reference ET Zones (optional)

Purpose: Intersects honeycomb mesh and mapped basin layer (if present) and is used in conjunction
with “Resources > Reference ET” folder. Like rainfall data, reference ET data can be varied both
spatially and temporally with this option. A text file is created for each zone and includes a time
history of appropriate meteorological data or reference ET data. The files are placed in the resources
folder as shown below. In this example, the map layer should include four polygons with the names
“Citrus_Springs”, “Dade_City”, “Inverness”, and “Zephyrhills”, each polygon representing the
geographical extents of each weather station. (see Section 6.2 for reference ET file specifications)

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Reference ET stations apply only if the “Include Evapotranspiration” box is checked as shown below.
It is possible to use a single reference ET station by checking the box as shown below and typing the
name of the station. A text file must be placed in the resource folder with the appropriate data.

20.2.8 Crop Coefficient Zones (required when ET is included)

Purpose: Intersects honeycomb mesh and mapped basin layer (if present) and is used in conjunction
with the “crop coefficient” lookup table. In addition to crop coefficients, root depth and irrigation
parameters are set. Often, the land cover zone map layer can be used for crop coefficient zones.

It is possible to use a single crop

coefficient zone by checking the
box as shown above and typing the name of the zone to be included in the model. In this example,
the zone “Citrus” must be included
in the appropriate crop coefficient
lookup table.

Corresponding Lookup Table(s):

Crop Coefficient Sets. (see Section
7.8)

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©2017, Streamline Technologies, Inc.
User’s Manual and Technical Reference
Volume 2, Chapter 21
Overland Flow Graphic Elements

September 2017

© 2017, All Rights Reserved

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
21. Overland Flow Graphic Elements

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Contents
21. Overland Flow Graphic Elements ............................................................................................... 5
21.1 Exclusion ............................................................................................................................... 7
21.2 Extrusion ............................................................................................................................... 9
21.3 Breakpoint ............................................................................................................................. 9
21.4 Breakline ............................................................................................................................. 10
21.5 Pond Control Volume .......................................................................................................... 13
21.6 Channel Control Volume ..................................................................................................... 16
21.7 Channel (Feature) .................................................................................................................17
21.8 Cove .................................................................................................................................... 18
21.9 1D Node Interface ............................................................................................................... 18
21.10 Weir (Feature) .................................................................................................................... 20
21.10.1 Drawing a Weir Feature ............................................................................................... 21
21.11 Basin Interface Point .......................................................................................................... 23
21.12 Basin Interface Line ........................................................................................................... 23
21.13 Mapped Basin (Feature) ..................................................................................................... 24
21.14 Boundary Stage Point ........................................................................................................ 25
21.15 Boundary Stage Line.......................................................................................................... 25
21.16 External Hydrograph Point ................................................................................................ 27
21.17 External Hydrograph Line .................................................................................................. 28
21.18 Simplification Feature ....................................................................................................... 28

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21. Overland Flow Graphic Elements

Overland flow graphic elements are used to: (1) characterize the terrain; (2) interact with 1D
elements; (3) establish boundary conditions; and, (4) simplify an existing mesh. They are the basis
for mesh construction.

The following dropdown list is taken from ICPR’s Graphic View and depicts the options specifically
related to 2D overland flow. It is possible to have multiple regions for a given project. Graphic
elements are always placed on the active region for the active scenario. Typically, only one scenario
is used for a project. However, if more than one is used, then you must set the active scenario in the
bottom right corner of the main ICPR window. Graphic elements are created by first setting the
“active graphic element” and then clicking the “create graphic element” icon. Instructions appear in
a prompt at the lower-left corner of the graphic view editor after clicking the create icon.

It is possible to create all the 2D overland flow graphic elements (except the weir feature) in a GIS
and then import them to ICPR via shapefiles or CSV files. To do this, expand “Feature Types” on the
data tree below “Overland Flow Regions” as shown below. Move the cursor over any of the features
(except “Weir (Feature)”) and right click. Then select “Import Shape(s) – Create New” and follow the
instructions. Note that there are other tools available, depending on the feature type. For example,
you can export a shapefile for most features by selecting “Generate Shape”.

Attribute tables are not included when importing and exporting shapefiles.

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If a projection file is included with a shapefile and if a CRS is set for the ICPR project, the shapefile will
automatically be spatially translated into the ICPR CRS at the time of import. However, if you change
the ICPR CRS after importing the shapefile, the spatially data will not be re-projected to the new CRS.

The objective of the triangular mesh is to form a reasonable approximation of the ground surface.
More vertices in the mesh do not necessarily make for a more accurate or better model. You must
keep in mind that water moves along the edges of triangles and invert elevations of those edges are
based on ground elevations at the vertices as determined from the DEM. It is important to capture
important topographic features that affect the storage and movement of water. For example, there
is a large depression near the center of the figure shown below (light yellow) that has an east-to-west
drainage ditch as an outfall along its western shore. It is important to place triangle sides along the
bottom of that ditch to allow an outlet for the depression. Otherwise the depression would hold
more water numerically than it would naturally. Also, it is generally important to capture toe of slope
and top of bank around storage systems, local ridges and significant changes in slope.

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As discussed in Section 12.1.2 of this document, time-stage nodes become outlets for the model
domain. A relationship between time and known stage elevation is established in the form of a table.
A similar approach is used for 2D overland flow regions, except boundary stages can be established
at either a point or along a line. ICPR has graphic elements for both of these.

Another type of boundary condition is the specification of known flow rates as a function of time.
These are called “external hydrographs” and for 2D overland flow regions, these can be specified at
a point or along a line.

Graphic elements should never be placed outside of, or cross

over, their respective overland flow region boundary.

The following sections describe each of the various 2D overland flow graphic elements.

21.1 Exclusion
Exclusions are closed polygons within an overland flow region. The area inside an exclusion graphic
element is “excluded” from the triangular mesh generation process. Consequently, there can be no
overland flow across an exclusion polygon. Furthermore, exclusions do not contribute stormwater
runoff to the region. Overland flow is permitted along its perimeter.

An example application of the exclusion feature is shown below. A wastewater effluent disposal
system is bermed around its perimeter. Stormwater runoff from adjacent areas must flow around
the outside of the berms and no discharge is expected from the site. An exclusion feature is created
along the top of the berm as shown below on the right.

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The resulting triangular mesh is shown below and does not extend into the exclusion polygons, but
links are created along the perimeter, allowing flow along the berms but not across them.

Exclusions can share edges with pond and channel control volumes. Vertex points of the triangular
mesh are placed at each coordinate point of the exclusion and overland flow links are established
along the edges of the exclusion, except where those edges are shared with pond or channel control
volumes. Exclusions must be located completely inside the region boundary and not touch the
boundary.

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21.2 Extrusion
Extrusions are very similar to exclusions. They are formed by closed polygons and no overland flow
is permitted to cross the polygon. Flow is permitted around the perimeter. The difference between
exclusions and extrusions is that
stormwater runoff is permitted from an
extrusion polygon. ICPR assumes the
extrusion is 100% impervious with no
initial abstraction. Flow is distributed
proportionately to each of the vertices
along the extrusion polygon based on a
line weighting. The area enclosed by the
extrusion polygon does not interact with
the 2D overland flow model.

Extrusions are useful for incorporating

impediments to overland flow such as
buildings as shown in the example to the
right.

Extrusions must be located completely inside the region boundary and not touch the boundary. No
other graphic element should intersect exclusions, although it is permissible to snap the endpoint of
a breakline to an exclusion vertex. It is also possible for extrusions to share sides with pond and
channel control volumes, but at least 2 vertices should be shared.

21.3 Breakpoint
Breakpoints are added for refinement of the triangular mesh and can be placed anywhere within an
overland flow region including inside pond and channel control volumes. However, breakpoints

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placed inside exclusion and extrusion polygons and weir features are ignored. Vertices are
guaranteed at breakpoints. Honeycombs are formed around vertices and therefore a honeycomb is
formed around a breakpoint.

Patterns of breakpoints can be placed by pressing

“Z” after clicking the “Create Graphic Element” icon
when the breakpoint graphic element is active.
Either a fixed rectangular pattern or triangular
pattern with equal sides can be used to create the
breakpoints. The breakpoint pattern can be limited
to an “active fence” by checking the box shown to
the right. An entity buffer can (and should) also be
specified as shown, that is used as a minimum
distance between a breakpoint and any other visible
graphical features.

21.4 Breakline
Breaklines, like breakpoints, are used to refine the
triangular mesh. Although they can be placed
anywhere inside the overland flow region, they are
typically placed along low-lying collection paths and local ridgelines. Triangle vertices are
guaranteed at each coordinate point of the breakline. Furthermore, triangle edges, and
consequently overland flow links, are guaranteed along the breakline. A breakline can also be
placed parallel to a contour at significant slope changes. This tends to create overland flow links
generally perpendicular to the contours.

The following is an example of breaklines placed along the bottom of a tributary to a lake. The
breaklines are snapped at confluence points. Breakpoints are used near the top of bank to pick up
the change in grade along the side slopes of the channels. The resultant triangular mesh is also
shown along with down gradient arrows indicating the likely flow direction.

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It is a good practice not to cross other 2D overland flow map features with breaklines such as pond
control volumes, channel control volumes, exclusions, etc.

The original vertices along the breakline shown below are numbered 11, 12, 13, 14 and 15. An
additional vertex was inserted between points 14 and 15 as part of the triangle refinement process.
Ground elevations at each original vertex are automatically obtained from the associated DEM.
Elevations for inserted vertices can either be obtained directly from the DEM (the default), or they
can be interpolated from ground elevations at the two adjacent original vertices. To interpolate,
double click the breakline you want to set to open its data form. And then check the “interpolate”
box. You also have the option to set a specific roughness zone for the entire breakline by checking

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the “Override Roughness Zone” box and typing a name on the form and then adding that name to
the roughness lookup table.

There are ArcHydro tools that will find ridges and valleys from a DEM, both important in 2D
modeling. Although these can be imported to ICPR from a shapefile, typically the density of points
defining those lines is too great to be of any practical benefit without some thinning.

ICPR includes a “Simplify” tool that can be used to thin breaklines with high densities of points. The
tool is accessed by right clicking “Breakline” as shown below and then clicking “Simplify”. A selection
of breaklines is made and then the “Simplify Breaklines” dialog box opens as shown below. Typically,
“Make Interpolatable” and “Preserve Intersections” are checked and a “Max Vertex Spacing is
specified. The make interpolatable option will activate the “Interpolate” check box on the “Overland
Flow Breakline Feature Data” form described above.

The black lines on the left are the original breaklines from ArcHydro. The heavy blue lines on the
right are the thinned out breaklines using the “Simplify” tool in ICPR.

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ArcHydro Generated Breaklines ICPR Simplified Breaklines

Another example is shown below where breaklines are used to characterize the terrain for a relatively
steep area. In general, the breaklines are placed perpendicular to the contours from uphill to
downhill.

21.5 Pond Control Volume

Pond control volumes are used to incorporate “level pool” hydraulics inside a 2D overland flow
region. They must be closed polygons. Triangle vertices are guaranteed at each coordinate point
along the polygon. However, overland flow links are not included along the edges of the polygon.
Although the triangular mesh extends into the control volume, no overland flow links are created
inside of it. The mesh inside the control volume is used strictly to build the honeycomb for hydrologic
purposes (infiltration and rainfall excess calculations).

Pond control volumes are “attached” to a 1D node. The 1D node (stage/area node type) must be
created before the pond control volume is drawn. It is important that the largest area in the stage-
area table not exceed the area of the pond control volume polygon. For example, if the pond control

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volume is placed roughly at the 40-foot contour and encloses an area of 25 acres, then the stage area
table should have a point at elevation 40 feet with a corresponding area of 25 acres.

Pond control volumes can share common sides with other pond control volumes and graphical
elements, but those sides must match exactly point-for-point. An error will occur if two control
volumes (pond or channel) touch at only a single point. Pond control volumes can also share a common
edge with the region boundary, but they should never cross over the region boundary.

There is an “Interpolate” option available for pond control volumes that works the same as the
interpolate option for breaklines. When the “interpolate” option is unchecked, elevations for inserted
vertices along the perimeter of the pond control volume are obtained directly from the DEM (the
default). If the “interpolate” option is checked, then elevations for inserted vertices are interpolated
from ground elevations at the two adjacent original vertices. You can open the pond control volume
data form by double clicking on the graphic element or by clicking “2D Features > Overland Flow >
Pond Control Volumes”.

Breakpoints can be placed inside a pond control volume as shown below. A honeycomb is created at
each breakpoint and allows percolation to “climb” up the sides of the pond as water levels increase,
exposing different soil types.

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A stage-area table is required for all 1D nodes that have a pond control volume attached to them.
There is a tool in ICPR that will automatically extract stage-area tables for any or all pond control
volumes from a ground surface DEM. Right click on the pond control volume feature and select the
“Generate Stage/Area Table” option as shown below. A prompt for the selection set of pond control
volumes appears at the bottom of the graphic view. The “Generate Stage/Area of Nodes” dialog box
appears where you specify a surface DEM and stage spacing (vertical increment in feet or meters).
The stage-area tables for corresponding nodes are automatically updated.

Always keep in mind that the stage-area table is only as good as the DEM. If the DEM was derived
from standard LiDAR, bathymetry below the waterline will likely not be available, which, is an
important consideration for continuous simulation modeling.

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21.6 Channel Control Volume

The advantage of 1D channel links in certain situations is that detailed cross sections can be used to
more accurately represent the channel geometry for in-bank conditions and the roughness
characteristics of the cross section can be
varied. If, however, wide flood plain areas
are expected outside of the main channel,
then 2D overland flow is more appropriate.
ICPR uses the channel control volume
feature as the mechanism to interface 1D
and 2D hydraulics.

Typically, 1D nodes are placed along a

channel first and then connected with 1D
channel links. The channel control volumes
are closed polygons attached to a 1D node
and generally extend halfway upstream and
downstream of the channel links connected
to or from a given node. A channel control
volume should never encompass more than a single 1D node. The outer edges of the control
volume generally follow the top of bank of the channel, but can be extended farther out if the
modeler believes the 1D channel cross section beyond the channel bank is important to include in
the 1D hydraulics. Flow is transferred between the 2D overland flow links and 1D nodes along the
edges of the channel control volumes.

It is important to understand that every vertex along the channel control volume becomes a point
where water can move between the 2D mesh and the 1D system. Consequently, care should be taken
to include local high and low points from the ground DEM.

Adjacent channel control volumes sharing a common side should match exactly along that common
side. An error will occur if two control volumes (pond or channel) touch at only a single point. You can
use the “trace” feature while drawing the polygons to accomplish this. Any gaps between the
adjacent control volumes will be filled with tiny triangles that can lead to other problems.

Channel control volumes can share common sides with pond control volumes and other graphical
elements, but those sides must match exactly point-for-point. An error will occur if two control
volumes (pond or channel) touch at only a single point. Channel control volumes can also share a
common edge with the region boundary, but they should never cross over the region boundary.

There is an “Interpolate” option available for channel control volumes that works the same as the
interpolate option for breaklines and pond control volumes. When the “interpolate” option is
unchecked, elevations for inserted vertices along the perimeter of the channel control volume are
obtained directly from the DEM (the default). If the “interpolate” option is checked, then elevations

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for inserted vertices are interpolated from ground elevations at the two adjacent original vertices.
You can open the channel control volume data form by double clicking on its graphic element or by
clicking “2D Features > Overland Flow > Channel Control Volumes”.

Like pond control volumes, the triangular mesh is extended into the channel control volume, but only
for purposes of constructing the honeycomb. Overland flow links are not included inside the control
volume or along the edges. Vertices are guaranteed at each coordinate point along the outer edges
of the control volume.

Breakpoints and breaklines are permitted inside the control volume to further refine the honeycomb.
However, breaklines should not cross channel control volumes.

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21.8 Cove
Coves are “backwater” areas along 1D
channel links that are not appropriate for 2D
modeling and not significant enough to
include in the 1D modeling effort. It is
assumed that the water surface inside the
cove behaves as a level pool at an elevation
equal to the connection point along the 1D
channel. Coves “live” inside channel control
volumes. Consequently, they are specified in
terms of a starting index and ending index of
points along the control volume, plus the
connection point. The numeric order of each
point along the channel control volume will
appear when selecting the starting index for
the cove. Always select the lower index
number for the starting index and the higher
index number for the ending index. The water
surface inside the cove is assumed to be flat
at an elevation interpolated from the water surface along the 1D channel link at the cove
connection point. The wetted surface area inside the cove is not automatically included in the
numerical computations. It should be added to the stage/area node associated with the respective
channel control volume.

21.9 1D Node Interface

The 1D node interface graphic element allows 1D links to be connected to the 2D mesh. Also,
traditional basin hydrographs can be assigned directly to the 1D node interface as if it were a standard
1D node. Vertices are automatically placed at all 1D node interfaces.

To illustrate this concept, consider the figure shown below. A storm sewer system includes surface
inlets, catch basins/manholes, and pipes. A “1D Node Interface” graphic element is placed at each
inlet (shown as a black X). Catch basins and manholes are modeled as standard 1D stage/area node
types (shown as solid blue circles). 1D links are used to connect a 1D node interface to any other 1D
node in the model. For example, the storm inlets (black X’s) are connected to the catch
basins/manholes (blue circles) with weir links. 2D surface flow moves to the inlets, drops through the
weir into the catch basin and then through the pipe system. Since drop structures are composite
links consisting of a weir in series with a pipe, they can be used at upstream terminus ends of the
storm sewer system to connect a 1D node interface feature to a stage-area node.

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The initial stage at 1D node interfaces are taken directly from the ground surface DEM. However,
you can override the default stage in the overland flow 1D node interface data form. Either double
click the 1D node interface graphic element or click “2D Features > Overland Flow > 1D Node
Interface” to open the data form. Check the “Override Initial Stage” box and type in the initial stage
you wish to use. It is important to use this option when you are modeling underground systems, like
a storm sewer system below a parking lot. Otherwise the initial stage will be based on the elevation
of the parking lot, resulting in substantial head on the pipe system at the start of any simulation and
high initial flows.

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21.10 Weir (Feature)

A weir feature is used to incorporate roadways, berms or walls into the 2D mesh without having to
model them as 2D overland flow links. The weir feature is input by specifying an offset, digitizing its
centerline and then designating the upstream side of the weir. ICPR constructs the 2D triangular
mesh around the weir feature. Overland flow is permitted along the edges of the weir feature, but
not across the weir. ICPR simultaneously constructs 1D weirs at each vertex along the centerline,
after the triangular mesh is constructed.

The following rules apply to weir features:

1. Weir features cannot abut or intersect one another.

2. Weir features, including their offsets, cannot touch the region boundary
3. Although weir features can touch pond and channel control volumes, it is the offset
(not the weir centerline) that must match the control volume exactly point for point
along common edges.
4. Other graphical elements such as breaklines should not intersect weir features.
5. 1D node interfaces can be snapped to a vertex along the offset lines but not placed
inside the weir feature.
6. Any 2D overland flow graphical point feature placed inside the weir feature will be
ignored when the mesh is constructed.

An irregular cross section is created for each 1D weir (created at each vertex along the centerline).
The cross sections consist of either 2 coordinate pairs for the ends of the weir feature, or 3 coordinate
pairs for the interior. The elevations at the vertices, by default, are taken from the ground surface
DEM – elevations at cross section points between the vertices are interpolated from the adjacent
vertices.

A vertical offset from the DEM elevations can be specified by opening the data form for the overland
flow weir feature (double click on it or click “2D Features > Overland Flow > Weirs”). The elevation
calculation method shown below allows you to set either a “Vertical Offset” (i.e. from the DEM) or a
“User Specified Elevation”. If the vertical offset method (the default method) is chosen, then the
vertical offset distance (f, m) must be specified. In the example below, the offset is set to zero feet,
so that the weir follows the DEM. The weir type and weir discharge coefficient are also set on the
overland flow weir feature data form.

If the water level at any vertex along the weir offsets exceeds its respective weir invert elevation, then
flow is possible across that 1D weir and water is moved across the weir at that location.

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21.10.1 Drawing a Weir Feature

Zoom in to the area of interest. The
centerline of the weir feature follows
the centerline of the roadway in this
example.

Set the active overland flow graphic

element to “Weir (Feature)” and click
the “Create Graphic Element” icon.

If the automatic naming is turned on, then the name will

set itself. An 18-foot offset is used. Note that roadside
swales exist approximately 18 feet off the centerline of
this roadway. Lines are automatically drawn parallel to
and on both sides of the centerline.

The weir feature is drawn from left (west) to right (east).

A point is included at the stream crossing. Press enter
after reaching the eastern extent. A prompt appears to pick the upstream side of the weir. The flow
is from south to north, so click anywhere on the south side of the roadway.

ICPR4 User’s Manual and Technical Reference, Volume 2 21-21

The weir type and weir discharge coefficient must be set. This is accomplished by opening the “Weir
(Feature)” data form. The type is set to “Broad Crested, Vertical” and the discharge coefficient to 2.8.

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21.11 Basin Interface Point

ICPR allows construction of hybrid models, models that combine traditional hydrology (e.g. NRCS
unit hydrograph method) with 2D overland flow. Either manual or mapped basins can be used for
traditional hydrology. A basin interface point allows you to discharge a portion or all flow from a
traditional basin to a specific location (i.e. a point) in the 2D overland flow mesh. A triangle vertex is
guaranteed at the point location.

Once you have placed the basin interface point, you need to identify the traditional basin you want
assigned to that point and the proportion of flow to be discharged to the 2D mesh. This is done by
basin interface point feature data form and filling out the appropriate parameters as shown above.
Note that a “1” is used to assign 100% of the basin flow.

If the proportion of flow is less than 1, then the basin flow is split accordingly between the basin
interface point and the 1D node that the basin is assigned to in the basin data form. For example,
assume that “Basin A” in the example above is assigned to stage/area node “ZZ” and that the
proportion of total flow parameter is set to 0.75. Then 75% of the runoff from “Basin A” will be
delivered to overland flow basin interface point “OFBPT-001” and 25% will be delivered to node “ZZ”.

21.12 Basin Interface Line

Like the basin interface point, this feature allows a portion or all of the flow from a traditional basin
to be distributed along a line in the 2D overland flow mesh. A triangle vertex is guaranteed at all
points along the line.

Once you have placed the basin interface line, you need to identify the traditional basin you want
assigned along the line and the proportion of flow to be discharged to the 2D mesh. The example
shown below assigns 80% of the flow from Basin A to the basin interface line (the remaining 20% is
delivered to the node assigned to “Basin A” in its data form). The flow is then distributed along the
line proportionally based on length. The proportional length assigned to a particular vertex is half
the distance to adjacent vertices divided by the total length of the line interface.

ICPR4 User’s Manual and Technical Reference, Volume 2 21-23

21.13 Mapped Basin (Feature)

The mapped basin feature works together with a polygon map layer (described in Section 20.2.5).
Mapped basins use traditional basin methods (e.g. NRCS unit hydrograph method) and are
embedded into the 2D overland flow region. Breakdowns of soil – land use intersections are
automatically derived with mapped basins.

The mapped basin feature is a closed polygon that

encompasses the extents of the traditional basins to be
embedded into the 2D overland flow region. It does not
include individual basins; that is accomplished with a map
layer. For example, the mapped basin feature in the
sketch to the right is the outer polygon formed along the
edges of the triangles. The mapped basin map layer
includes the polygons of each individual basin (e.g.
LAKE001, LAKE002, etc.).

It is possible for the mapped basin feature to exactly

match the overland flow region boundary. When this is
done, traditional hydrologic methods (e.g. NRCS unit
hydrograph method) replace 2D overland flow methods
for the entire region. This is a useful technique when
integrating traditional hydrology with 2D groundwater flow.

Mapped basins must be used to integrate traditional

hydrology with 2D groundwater flow.

ICPR allows 2D overland flow links along the edges of the mapped basin feature. Vertices are
guaranteed at each coordinate along the feature. Pond control volumes and channel control
volumes can be placed inside a mapped basin feature as well as straddle the edges of it.

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21.14 Boundary Stage Point

Stage elevations as a function
of time can be forced at any
location in the 2D overland flow
mesh by setting a boundary
stage point. A vertex in the
mesh is guaranteed at all
designated boundary stage
points.

Once you have placed the

boundary stage point, you need
to identify the table name that
contains the time-stage data (a boundary stage lookup table). This is done by specifying a boundary
stage table name in the boundary stage point feature data form shown above. The corresponding
lookup table is shown below. Refer to Section 7.1 for details of boundary stage tables.

21.15 Boundary Stage Line

Stage elevations as a function of time can be forced along a line in the 2D overland flow mesh by
setting a boundary stage line. Vertices in the mesh are guaranteed at all points along the line.
Overland flow links along a boundary stage line are disabled.

An example is shown below where two boundary stage line features are included at the eastern end
of the region bounday. Historical stage records for the large river east of the region boundary are
used as a boundary condition.

ICPR4 User’s Manual and Technical Reference, Volume 2 21-25

Once the boundary stage line has been placed, the table names at each end of the line that contain
the time-stage data (boundary stage lookup tables) must be entered. A dropdown list appears if you
right click in this data field. Linear interpolation based on distance is used between the two
endpoints. It is important that the first table correspond to the first point entered on the boundary
stage line and the second table correspond to the last point. This can be determined by using the
edit polyline tool. Click the edit polyline icon then click the boundary line feature. The points are
numbered in the order that they were entered. The table for “Boundary Stage 1” corresponds to
polyline point “0” and “Boundary Stage 2” corresponds to point “11” in the example shown below.

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21.16 External Hydrograph Point

External hydrograph point features are similar to basin interface point features, except instead of
the flow from a drainage basin, an external hydrograph (i.e. a time-discharge table) is specified. All
or a portion of the external hydrograph can be assigned to any location in the 2D overland flow
mesh by setting an external
hydrograph point. A vertex
in the mesh is guaranteed at
all designated external
hydrograph points. Specify
the table name and the
proportion of total flow (use
a value of 1.0 for 100%).

ICPR4 User’s Manual and Technical Reference, Volume 2 21-27

21.17 External Hydrograph Line

Like the external hydrograph point, this feature allows a portion or all of the flow from an external
hydrograph to be distributed along a line in the 2D overland flow mesh. A triangle vertex is
guaranteed at all points along
the line.

Once you have placed the

external hydrograph line, you
need to identify the external
hydrograph you want
assigned along the line and
the proportion of flow to be
discharged to the 2D mesh.
The flow is then distributed
along the line proportionally
based on length. The
proportional length assigned to a particular vertex is half the distance to adjacent vertices divided
by the total length of the line interface.

21.18 Simplification Feature

The simplification feature differs from other overland flow features in that it is not used to construct
the mesh. Instead, it is used to simplify an existing mesh by aggregating or clustering all nodes
within the simplification “polygon” and converting them to a single 1D stage/area node (level pool).
A stage-area table is automatically
constructed based on the links inside the
simplification feature and all links inside the
simplification feature are eliminated at run
time (not permanently), thus simplifying
the model. These are particularly useful for
unstable areas in pockets or depressions.
Furthermore, run times can be greatly
reduced because less links are involved, and
a larger computational time increment
might be possible.

An example is shown to the right with

comparisons of stage hydrographs for
locations A-D provided below. In this
example, there is very little difference
between the stage hydrographs yet the run
times were about 25 times faster with the simplifications activated. That, of course, is not always

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the case and depends on the particular set of circumstances. Also, friction and other losses are not
included inside the simplification feature.

Each time a simplification feature is created, it is active by default. Individual features can be
deactivated by opening its data form (click “2D Features > Overland Flow > Simplifications”) and
uncheck the “Active” box (shown below left).

An option is available when you execute a simulation as to whether simplifications will be included.
A box labeled “Activate Simplifications” must be checked (shown in yellow below right) to include all
“active” simplifications in a particular simplification.

ICPR4 User’s Manual and Technical Reference, Volume 2 21-29

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©2017, Streamline Technologies, Inc.
User’s Manual and Technical Reference
Volume 2, Chapter 22
Mesh Construction and Parameterization

September 2017

© 2017, All Rights Reserved

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
22. Mesh Construction and Parameterization

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22-2 ICPR4 User’s Manual and Technical Reference, Volume 2

Contents
22. Mesh Construction and Parameterization .................................................................................. 5

ICPR4 User’s Manual and Technical Reference, Volume 2 22-3

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22. Mesh Construction and Parameterization

The scenario manager has two primary functions: (1) it allows you to add new scenarios to a project;
and, (2) it performs the “build” function which constructs all meshes and parameterization for all
regions living in each scenario. Basically, this is the final step
prior to executing a simulation for 2D models.

It is important that the raster view be turned off for all polygon
map layers that are to be included in the build and animations must be turned off. Otherwise errors
will occur.

To “build” a scenario, open the scenario manager, select the scenario you wish to build, and click
the build button in the lower left corner of the simulation manager as shown to the left.

The scenario build dialog box appears after clicking the build button. There are just 2 options: (1)
Check Intersections; and, (2) Generate Build XML. The check intersections option is for situations
like a breakline crossing a pond control volume. If you are certain you don’t have situations like this
then it is better to leave the “Check
Intersections” unchecked because the
build will be faster. If you check this
box and it intersections are found,
then ICPR will automatically insert a
new vertex at the intersection point.
You can almost always leave
“Generate Build XML” unchecked.
This is used occasionally for
debugging purposes, but will slow the
build process down substantially for
large projects.

ICPR4 User’s Manual and Technical Reference, Volume 2 22-5

Click the “Build” button to proceed. You may get the following message if a scenario build was
previously performed.

Messages appear as the build progresses, with the last message being “Build Complete” as shown
below. The build process can take just a few seconds or several hours, depending on the complexity
of the project.

Any change to 2D features including parameters specified in their data forms (except simplifications)
or to the region manager specifications require another build. For example, if you add or delete a
single break point you will need to rebuild the scenario before executing. Or, if you change the
roughness zone in the region manager, you will need to rebuild.

The “Status” button on the scenario manager indicates the version number of ICPR that was used to
construct the meshes and the log button provides details about a specific scenario build.

Once a scenario has been built, the “build” version of the triangular, diamond and honeycomb
meshes are available for viewing and can be toggled on and off from the data tree of the general tab
in the Graphic View. Furthermore, each of these meshes can be exported to a DXF file by right
clicking the preprocess label or build label. The DXF files can then be imported to GIS or CAD
programs.

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After a scenario build is completed, there are tools to query specific locations on a mesh for
parameterization information. You must first turn on the triangulation “build” mesh. Click the “2D
Node Info” icon shown below; then select a triangle vertex (either overland flow or groundwater), or
window around a group of them. For surface nodes, a breakdown of basin polygons is provided along
with their various attributes. An example is shown below.

The 2D Link Info tool can be used to query triangle edges for 2D overland flow meshes.

ICPR4 User’s Manual and Technical Reference, Volume 2 22-7

22-8 ICPR4 User’s Manual and Technical Reference, Volume 2

©2017, Streamline Technologies, Inc.
User’s Manual and Technical Reference
Volume 2, Chapter 23
Overland Flow Example, Suburban Setting

September 2017

© 2017, All Rights Reserved

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
23. Overland Flow Example, Suburban Setting

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23-2 ICPR4 User’s Manual and Technical Reference, Volume 2

Contents
23. Overland Flow Example, Suburban Setting ................................................................................ 5
23.1 Background ........................................................................................................................... 5
23.1.1 Acknowledgements ........................................................................................................ 5
23.1.2 Open Project ................................................................................................................... 6
23.1.3 Basic Workflow ............................................................................................................... 8
23.2 Base Data .............................................................................................................................. 8
23.2.1 Background Images ........................................................................................................ 8
23.2.2 Ground Surface DEMs .................................................................................................... 9
23.2.3 Map Layers ................................................................................................................... 10
23.2.4 Lookup Tables .............................................................................................................. 12
23.3 1D Model Setup ................................................................................................................... 14
23.3.1 1D Nodes (Stage/Area and Time/Stage Nodes) ............................................................. 14
23.3.2 1D Node Interface Points .............................................................................................. 14
23.3.3 Links ............................................................................................................................. 16
23.3.4 Basins ............................................................................................................................17
23.3.5 Boundary Conditions .....................................................................................................17
23.4 2D Model Setup................................................................................................................... 18
23.4.1 Overland Flow Region Boundary................................................................................... 19
23.4.2 Pond Control Volumes .................................................................................................. 21
23.4.3 Channel Control Volumes ............................................................................................. 21
23.4.4 Channel Interpolation Feature ...................................................................................... 23
23.4.5 Extrusions ..................................................................................................................... 23
23.4.6 Breaklines ..................................................................................................................... 24
23.4.7 Breakpoints................................................................................................................... 25
23.4.8 Boundary Stage Line .................................................................................................... 25
23.5 Overland Flow Region Manager .......................................................................................... 27
23.6 The Scenario Build (Mesh Construction) .............................................................................. 29
23.7 Simulation Control and Execution ....................................................................................... 31
23.7.1 General Tab................................................................................................................... 31
23.7.2 Output Increments........................................................................................................ 32

ICPR4 User’s Manual and Technical Reference, Volume 2 23-3

23.7.3 Resources & Lookup Tables ........................................................................................... 32

23.7.4 Tolerances & Options .................................................................................................... 32
23.7.5 Simulation Execution .................................................................................................... 32
23.8 Analysis of Model Results .................................................................................................... 33
23.8.1 Mass Balance Report ..................................................................................................... 33
23.8.2 Flood Depth Animations ............................................................................................... 35
23.8.3 Generating a Maximum Flood Elevation DEM ............................................................... 38
23.8.4 Velocity Vector Animation ............................................................................................ 42
23.8.5 Quick Charts ................................................................................................................. 43
23.8.6 Aggregate Flow ............................................................................................................44

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23. Overland Flow Example, Suburban Setting

23.1 Background
The study area (283 acres) for this example is
shown to the right and is in the City of
Tallahassee. It is bordered by the CSX railroad
on the south and the Park Avenue ditch
crosses the southeast corner. This area has
historically experienced frequent flooding
along Violet Street and along Riggins Road. A
photograph on file with the City of Tallahassee
(shown below) depicts flooding at 695 Violet
Street on January 21, 2010. This flooding is not
caused by overbank conditions along a
waterway, but rather from insufficient capacity
of the storm sewer system.

The purpose of this example is to describe the 2D model setup procedure in ICPR, including an
interface with 1D drainage components such as underground storm sewers, open channel ditches
and retention/detention ponds.

23.1.1 Acknowledgements
The lead consultant and Engineer-of-Record for this project was Singhofen & Associates, Inc. (“SAI”)
of Orlando, Florida. SAI provided all base information for this investigation to Streamline
Technologies, Inc. including but not limited to: 1-foot DEMs for existing conditions and various
alternative conditions; shapefiles for land cover/impervious areas, soils and underground
infrastructure; and time-stage data for model boundary conditions. The City of Tallahassee provided

ICPR4 User’s Manual and Technical Reference, Volume 2 23-5

historical rainfall data and stream gage data and complaint files for the study area as well as original
LiDAR and various base GIS layers such as parcel maps.

23.1.2 Open Project

Open the following project.

The coordinate refence system for this project is “NAD83(HARN) / Florida North (ftUS). You can
verify this by hovering over the CRS in the lower right corner of the main ICPR window.

Open the Graphic View, maximize it and apply the following “Graphic View Port Settings”.

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You should see something like the following. This is the existing condition 1D nodal network and
includes the storm sewer system, open channel system and a few stormwater ponds. The 1D model
setup is discussed in Section 23.3. A “Parcel Map” layer is toggled on and used for reference
purposes only.

ICPR4 User’s Manual and Technical Reference, Volume 2 23-7

23.1.3 Basic Workflow

The following basic workflow is typical of most 2D overland flow projects, although the sub-tasks
vary depending of objectives and project specifics. A description of the various tasks outlined below
and as they relate to this example is provided in the following sections.

1. Prepare Base Data

a. Aerial Background Images
b. Ground Surface DEM
c. Map Layers
i. Soil Zones
ii. Land Use / Land Cover Zones
d. Lookup Tables
i. Rainfall Excess Set (Curve Numbers)
ii. Impervious Set
iii. Roughness Set
2. Prepare 1D Nodal Network
a. 1D Nodes (Stage/Area & Time/Stage)
b. 1D Node Interfaces (1D/2D interface points)
c. 1D Links
d. Basins
e. Boundary Conditions
3. Prepare 2D Graphical Elements
a. Interface with 1D Components
i. Pond Control Volumes
ii. Channel Control Volumes
iii. Channel Interpolation Features
b. Terrain Characterization
i. Extrusions
ii. Breaklines
iii. Breakpoints
c. Boundary Conditions
i. Boundary Stage Line
4. Overland Flow Region Manager and Preprocess Mesh
5. Scenario Build (Final Mesh Construction & Parameterization)
6. Simulation Control and Execution
7. Analysis of Model Results

23.2 Base Data

23.2.1 Background Images
The Background Image Manager is used to manage images such as aerials. “Origin X” and “Origin Y”
is the location of the lower left corner of each background image panel. Notice that “Origin Z” is set
to -100. This drops the image below all other graphical elements. The “Width” and “Height” are the
dimensions in units of feet. The opacity can be adjusted to fade the images into the background.
Refer to Appendix A for details regarding extracting and preparing aerial imagery in GIS.

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The background images can be toggled on and off under the general tab of the graphic view as shown
below.

23.2.2 Ground Surface DEMs

A terrain surface layer (DEM) can be viewed by opening the “Raster” panel on the Graphic View and
checking the “Surfaces > Ground_88_5ft > Raster” box shown circled in red below. Note that in the
screen capture below, the “Surface Dynamic Zoom” is set to “Viewable Legend” and the “Opacity” is
set to “50%”. A 5-foot DEM is used for this example. The color palette can be changed using the
“Palette Selector” tool.

ICPR4 User’s Manual and Technical Reference, Volume 2 23-9

23.2.3 Map Layers

There are 3 map layers in this example: (1) Parcels; (2) Soil Zones; and (3) Impervious Zones. As
already mentioned, “Parcel Map” is for reference purposes. Map layers are created, imported and
rasterized in the Map Layer Manager. The rasterized version of the soil and impervious map layers
are intersected with the 2D computational meshes for parameterization purposes. Notice that the
“Cell Size” is set to “1” for “Soil Zones” – that is the raster cell size (i.e. 1-foot by 1-foot square cells).
It is set to “0.25” for “Impervious Zones” because the polygons are much smaller. It is always a good
idea to check the box below “Edit Lock” for each map layer after it has been imported and rasterized.
This prevents inadvertently deleting line work or labels.

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The map layers were imported from shapefiles and can be viewed in vector form by toggling on their
respective polylines as shown below. Do not turn the labels on for the “Impervious Zones” or the
“Parcels” …it will be very slow because of the extremely large number of text labels.

You can view the raster version of the map layer on the “Raster” panel of the Graphic View as shown
below. The zone description at the cursor location appears in the lower right corner of the Graphic
View.

ICPR4 User’s Manual and Technical Reference, Volume 2 23-11

23.2.4 Lookup Tables

There are three lookup tables that are needed for parameterization of the computational mesh: (1)
impervious percentages; (2) curve numbers; and (3) roughness coefficients for overland flow.

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The complete set of CNs used in this example are shown below.

ICPR4 User’s Manual and Technical Reference, Volume 2 23-13

23.3 1D Model Setup

23.3.1 1D Nodes (Stage/Area and Time/Stage Nodes)
Stage/Area nodes are used along a channel that parallels the CSX railroad. They are also used for
closed manholes and catch basins along the storm sewer system and for various stormwater ponds
throughout the study area. There are two time/stage nodes at the eastern end of the study area. One
serves as an offsite inflow point and the other is the model discharge point as shown below.

23.3.2 1D Node Interface Points

Storm inlets are modeled as weir links in this example and are connected to 1D stage/area nodes that
represent the bottom of catch basins below the storm inlets. 2D overland flow is used in the streets
up to the storm inlets. A special 2D graphic element is required to transfer water from the 2D

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computational mesh to the 1D nodal network. It is called a “1D Node Interface”. These are placed at
every storm inlet.

The 1D node interface points appear as X’s as shown below. A weir link is connected “from” the 1D
node interface point (“N042.1VS”) at street level and “to” the stage/area node (“N042VS”) at the
bottom of the catch basin. Pipe links are connected from and to the stage/area nodes below the
ground. Later, during the mesh construction process, a triangle vertex (2D node) is placed at 1D node
interface point.

The throat of the storm inlet is below the street elevation and is set in the weir data form as its invert
elevation. However, ICPR uses the street elevation (obtained from the DEM) at the 1D node interface
as the initial stage at that location unless an adjustment is made. The initial stage should be set at
the throat elevation. The adjustment is made in the 1D node interface data form.

The data form for the 1D node interface point (“N042.1VS”) is shown below. The weir data form for
link “W042.1VS” is also shown. Notice that the “Override Initial Stage” option is checked and that
the initial stage is set to 110.38 feet, which corresponds to the weir invert elevation. The warning
stage is also set to 110.38 feet in this example.

ICPR4 User’s Manual and Technical Reference, Volume 2 23-15

The 1D node interface point data forms can be accessed from the menu system as follows. There are
69 1D node interfaces in this example.

23.3.3 Links
There are 155 1D links in this model including channels, pipes, weirs, drop structures and a rating
curve. The rating curve link represents a bridge under the CSX railroad at the Park Avenue Ditch
located in the southeast corner of the study area. The bridge is hydraulically represented as a family
of rating curves reflecting a relationship between headwater elevation, tailwater elevation and flow

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rate. These were obtained from an older ICPR3 model of the Park Avenue Ditch system. Irregular
channel cross sections are used to describe the geometry for the various channel links. These were
field surveyed.

Weirs are used to model storm inlet hydraulics as previously mentioned. Consider the sketch shown
below. The catch basin below ground is modeled as a stage/area node and pipes are connected to it
and from it. Flow on the street moves overland and drops into the inlet and catch basin. The inlet in
the example below is modeled as a vertical weir with a 0.5-foot (6 inches) vertical opening that is 9
feet wide. This link behaves as a weir until the inlet is completely submerged and then it transitions
to orifice flow.

Street flow in this example is modeled as 2D overland flow. Consequently, a standard 1D stage/area
node cannot be used in the street. A special 2D graphical element called a “1D node Interface” is
needed as discussed in the previous section.

23.3.4 Basins
Since this project is modeled as 2D overland flow, no traditional basins are required or used in this
example.

23.3.5 Boundary Conditions

As stated previously, there are 2 time/stage nodes in this example, both at the eastern end of the
project. One is located at an offsite inflow point and the other is at the discharge point for this

ICPR4 User’s Manual and Technical Reference, Volume 2 23-17

example. Both are along the Park Avenue Ditch. Two boundary stage sets are used in this example
as shown below – one for the 25-year storm and the other for the 100-year storm. To view the various
tables within a given set, open the “Boundary Stage” tab. Data for these tables were obtained from
a regional model of the Park Avenue Ditch.

The boundary stage tables are referenced on the node data form as shown below.

23.4 2D Model Setup

Various graphical elements and features are used to interface with 1D model components,
characterize the terrain and establish boundary conditions. They are the basis for mesh construction.

The following dropdown list is taken from ICPR’s Graphic View and depicts the options specifically
related to 2D overland flow. Graphic elements are created by first setting the “active graphic

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element” and then clicking the “create graphic element” icon. Instructions appear in a prompt at the
lower-left corner of the Graphic View after clicking the create icon.

The overland flow region boundary must be created first before any graphical elements
are added. Graphical elements should never be drawn outside of their region.

Graphic elements can also be imported from

shapefiles by right clicking on a specific overland flow
feature on the data tree and selecting “Import
Shapefile(s) – Create New” like that shown to the
right for extrusions.

23.4.1 Overland Flow Region Boundary

At least one overland flow region must be created to
model 2D overland flow. A region is a closed polygon
that encompasses the extents of the area to be
modeled. Think of it as a watershed boundary.

There are two primary ways to create an overland flow region. The first is to draw it in ICPR and the
second is to import either a shapefile or a DXF file.

ICPR4 User’s Manual and Technical Reference, Volume 2 23-19

The Overland Flow (OF) Region Boundary is shown below in red, superimposed with the parcel map
layer.

Click the “Entity ID” icon and then click the region boundary. The perimeter length (18,978 feet) and
area (283 acres) of the polygon appear in an information window.

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23.4.2 Pond Control Volumes

A pond control volume is a polygon that is related to a specific 1D stage/area node and it serves as an
interface between 1D and 2D flow. A level pool assumption is made inside the pond control volume
and triangle edges within the pond control volume are removed from the 2D computations. This
eliminates a lot of unnecessary computations.

An example pond control volume is shown to the

right. A pond control volume can share an edge
along the region boundary, but it must match
exactly (point for point) along the common edge.
If the pond control volume must touch the region
boundary, at least 2 successive points must be
placed on the region boundary. Also, the pond
control volume cannot cross the region
boundary.

Pond control volumes can be toggled on and off under the “Feature Types” as shown below.

23.4.3 Channel Control Volumes

Channel control volumes are like pond control volumes in the sense that they are related to specific
1D stage/area nodes and they serve as an interface between 1D and 2D surface hydraulics. The
difference is that the water surface inside a channel control volume is sloped instead of a level pool.

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An example channel control volume is shown below. Note that channel control volumes can and
normally do share a common side. They can also share common sides with pond control volumes and
region boundaries. It is important that common edges match exactly without any gaps and that at
least 2 points are placed on common edges. Notice also that channel control volumes extend
approximately halfway upstream and downstream along any 1D channel links connected to or from
the respective node.

Channel control volumes should be approximately as wide as the cross section used for the 1D
channel links. The cross sections should not extend an appreciable distance beyond the channel
control volume and into the 2D overland flow area, otherwise storage would be double accounted.

Channel control volumes can be toggled on and off under the “Feature Types” as shown below.

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23.4.4 Channel Interpolation Feature

As mentioned in the previous section, the water surface inside a channel control volume can be and
usually is sloped. Consequently, a mechanism is needed to interpolate along that sloping water
surface. This is accomplished with a channel interpolation feature referred to as a “Channel
(Feature)”. This feature usually follows the
polylines describing the spatial alignment of 1D
channel links, but they can be drawn anywhere
the modeler feels it is appropriate.

An example channel interpolation feature is

shown to the right. Note that they are
superimposed with the 1D channel links and
appear as a yellow stripe in the sketch.

23.4.5 Extrusions
Extrusions are polygons and are used to model obstructions to overland flow, like buildings. They
are treated as 100% impervious and runoff from an extrusion is distributed along the perimeter of
the extrusion based on a line weighting. Although it is often possible to obtain a GIS layer with
building footprints, they usually need to be simplified before importing to ICPR to reduce the number
of vertices. Always keep in mind that a triangle vertex will be placed at every point in the extrusion
polygon.

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Several of the extrusions used in this example are shown below.

23.4.6 Breaklines
Breaklines are polylines used to characterize the terrain. Triangle edges are guaranteed along
breaklines. Recall that water flows along the triangle edges in ICPR. Breaklines are usually placed
along local valleys to define flow paths. They are also placed along local ridges to define drainage
divides.

Several of the breaklines used in this project are shown below. They are used along the roadways and
between houses.

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23.4.7 Breakpoints
A triangle vertex is guaranteed at each breakpoint. Like breaklines, they are used to characterize the
terrain and to refine the computational mesh.

Several of the breakpoints are shown below as black X’s.

23.4.8 Boundary Stage Line

Vertical walls are assumed along the overland flow region boundary unless other provisions are
incorporated into the model. A “Boundary Stage Line” is a polyline graphic element that can be used
to create an opening in the vertical wall. Triangle edges are guaranteed along the boundary stage
line and vertices are guaranteed at all points along the line. All vertices along the boundary stage line
are treated as time/stage nodes that are specified with a boundary stage table.

A single boundary stage line is used along the eastern end of the study area.

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The boundary stage line is shown below.

Two tables are required for a boundary

stage line graphic element, one at either
end. These tables are used to define the
time/stage relationships along the line.
Click “2D Features > Overland Flow >
Boundary Stage Lines” to open the data
form.

There are two blank data fields labeled

“Boundary Stage 1” and “Boundary Stage
2”. Right click inside either of these fields
to select from a list of available table
names. “East-BDZ” is used in both data
fields in this example.

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23.5 Overland Flow Region Manager

The overland flow region manager is used to assign the
various map layers and DEMs needed for final
parameterization for the region. Open the overland flow
region manager by clicking “Regions > Overland Flow Region Manager”. The diamond and
honeycomb cell sizes must be even multipliers of the various map layer cell sizes and the map layer
cell sizes cannot be less than the diamond and honeycomb cell sizes.

After the diamond and honeycomb

meshes have been created (in the
Scenario Build, discussed in the
following section), they are
rasterized for subsequent polygon
processing with other mapping
layers. The cell size data fields
establish the pixel size for this
rasterization process. In general,
these should be relatively small
numbers such as 1 foot or less. Just
keep in mind that these cell sizes
must be even multiples of polygon
map layer cell sizes. For example, if
the cell size for a land cover
polygon map layer is set to 4 feet,
then the diamond and honeycomb
cell sizes would have to be either
0.25, 0.50, 1, 2 or 4. Diamond and
honeycomb cell sizes should be less
than or equal to other map layer
cell sizes.

There are 2 surfaces (DEMs) that

need to be set in the region
manager: (1) the ground surface;
and, (2) the initial stage surface. If the overland flow plane is expected to be dry at the onset of the
simulation, then the ground surface DEM can be used for the initial stage surface. Otherwise a
separate DEM is required.

Preliminary triangle and honeycomb

meshes can be constructed by clicking the
“Preprocess” button at the lower-left

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corner of the region manager form. This is useful for evaluating triangle densities based on map
features prior to execution of the simulation.

Leave “Check Intersections” and “Generate Honeycomb” unchecked. Click the “Build” button at the
lower left corner of the “Preprocess” window. It will take a minute or two to construct the mesh.

A tool is available to help in your evaluation of the preliminary

triangular mesh. Click the “Search” tab located at the bottom left
corner in the graphic view. Make sure your “Preprocess Mesh” is
turned on by checking the appropriate boxes in the selection tree as
shown to the right. The “Triangular Layer Mesh Links” is located at
the bottom of the
“Search” tab. You
can search for
triangle sides less
than or equal to a specified maximum. The
example shown to the left has found 8 triangles
sides less than or equal to 5 feet, with the shortest
being 4.25 feet. The offending triangle side will
appear in the center of the graphic view editor.
You can decide at this point whether to change a

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2D feature such that the “short” triangle side is eliminated. For example, if you happen to have a
breakpoint very close to a breakline, you might want to delete the breakpoint.

23.6 The Scenario Build (Mesh Construction)

Final mesh construction and parameterization is done in the “Scenario Manager”. Open the scenario
manager.

Select the scenario you want to

build (“EXISTING” in this
example) and click the “Build”
button at the bottom left corner
of the scenario manager.

The “Scenario Build” progress

window will open. Click “Build”.
This is a relatively complex model
so it will take a few minutes to
construct and parameterize the
meshes.

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When the build is complete, click the “Exit” button and then close the scenario manager.

The final triangular and honeycomb meshes are shown below.

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23.7 Simulation Control and Execution

Two simulations are included in this example: (1) 025yr-08hr”; and, (2) “100yr-08hr. You can open the
Simulation Manager by clicking “Simulation > Simulation Manager”. There are 4 tabs in the
simulation manager. A brief description of pertinent details of each tab is discussed below.

23.7.1 General Tab

The simulation end time is 10 hours. The minimum and maximum calculation times for the surface
hydraulics are set to 0.01 and 2.561 seconds, which might seem a little odd. However, the
“FIREBALL” time marching scheme is used for this example and it determines the time step
individually for every node in the model. It works with time step levels, with the computational time
increment doubling for each successive level. Time steps for adjacent nodes can never be more than
1 time step level different. ICPR automatically constructs the time step levels from the min and max
computational time steps.

Time Step Level Time Step (sec)

1 0.01
2 0.02
3 0.04
4 0.08
5 0.16
6 0.32
7 0.64
8 1.28
9 2.56

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23.7.2 Output Increments

The output increments for surface hydraulics is 2.5
minutes.

23.7.3 Resources & Lookup Tables

These are the 4 lookup tables needed for this example
as shown to the right. The boundary stage set varies for
each simulation.

23.7.4 Tolerances & Options

As already mentioned, the FIREBALL
time marching algorithm is used. The “dZ
Tolerance” and the “Link Optimizer
Tolerance” are set to 0.0005 feet and
0.00001 feet, respectively. These values
are in smaller or tighter than those
typically used for the SAOR method.
Also, the dampening threshold is set to
0.05 feet which is a little larger than the
typical values of 0.005 feet, but well
within a reasonable range.

The “~fdot-8” rainfall distribution is

used with the “global” setting. The
rainfall amount is 7.4inches for the 25-
year storm and 8.9 inches for the 100-
year storm.

Close the simulation manager data form.

23.7.5 Simulation Execution

The simulations are ready to execute. Select all the simulations. This
will take about 5 to 10 minutes to run each simulation depending on
your computer … good time for a break once you get it running!

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23.8 Analysis of Model Results

23.8.1 Mass Balance Report
Click “Reports > Mass balance > Routing”.

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The maximum error percent for is a fraction of a percent (about 0.23%) which is not an issue.

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23.8.2 Flood Depth Animations

2D animations are accessed on the “Animation” panel in the Graphic View. Set the “Animation View
Mode” to “Max Depth” and the “Min Threshold” to 0.1 feet as highlighted in yellow below. The “Min
Threshold” filters out flood depths less than 0.1 feet deep.

Click the “Power” button (shown as location #1 to

the left) and then click the “End” button (location
#2). You should see the extents of flooding like
that shown below. Note that the background
images are toggled on with an opacity setting of
65%.

You can change the

color palette by
clicking the “Color
Palette Selector”.

Change the “Animation View Mode” to “Depth” and

“Go To Relative Time” = 3 hours. Repeat for hours 4, 5
and 6. Snap shots of each of these are shown below.

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ICPR4 User’s Manual and Technical Reference, Volume 2 23-37

Set the “Sleep Rate” to 0.1 sec (#1), click the “Rewind”
button (#2) and the “Play” button (#3) to animate the
flood depths. The sleep rate displays each output
increment at the designated time interval.

23.8.3 Generating a Maximum Flood Elevation DEM

Set the “Animation View Mode” to “Max Elevation”. Note that the “Min Threshold” is set to -9999
feet. This ensures that the full range of elevations will appear in the animation.

Click the “Power” button if it’s not already turned on, then click the “End” button.

Move the cursor anywhere over the animation and right click. The “Animation Export Form” appears.
Set the “File Root Name” to “Max_Elev_100yr”, set the “DEM Cell Size” to 5 feet and check the
“Generate DEM Hdr/Flt File Pair” box. Then, click OK.

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A notice appears when the operation is complete. Click OK. A DEM has been created and placed in
the “Surfaces” folder for the project.

Open the “Surface Manager” and click the “Batch Import” button.

ICPR4 User’s Manual and Technical Reference, Volume 2 23-39

Open the following file.

A message will appear, click import again.

There are now 2 surfaces.

Close the surface manager. Zoom into the area shown below and toggle the breaklines on. Click the
“Display Profile” icon and then select the breakline that is highlight below. This is along the centerline
of the roadway.

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Check both surfaces and then click OK. The 100-year water surface profile is shown below
superimposed with the ground surface profile. There is approximately 3 feet of flooding.

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23.8.4 Velocity Vector Animation

Set the “Animation View Mode” to “Velocity Vectors” and set the “Vector Scale Factor” to 2.5.

Make sure the “Power” is on and then “Go To Relative Time” 4 hours.

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Try playing an animation from the beginning with the sleep rate set to 0.1 seconds.

23.8.5 Quick Charts

Zoom into the area shown below, toggle the “Build” triangulation mesh on, and toggle the “1D Node
Interface” on.

Open the “Report” panel of the Graphic View. “Quick Charts” are in the middle of the panel. Set the
“Item Type” to “2D Nodes” and the “Chart Type” to “Stage”. Click the “Select/Display” button and
then move the cursor over the 1D node interface as shown below and click.

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23.8.6 Aggregate Flow

Flows can be aggregated using the “Multi-Item Report/Chart”. For example, assume we need the
total flow between the 2 houses shown below. Draw a fence around the 3 nodes (triangle vertices).
Set the “Report Category” to “2D Nodes – Aggregate” and click the “Add Item(s)” button. Notice
that the “Item Count” is now set to 3. Click the “Reports Form” button.

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Make the following setting and then click “View Chart”.

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The discharge hydrographs for the 2 storms representing the total inflow to the 3 selected nodes is
shown below. They peak at about 47 cfs and 76 cfs for the 25-year and 100-year storms, respectively.

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©2017, Streamline Technologies, Inc.
User’s Manual and Technical Reference
Volume 2, Chapter 24
2D Groundwater, Concepts and Theory

September 2017

© 2017, All Rights Reserved

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
24. 2D Groundwater, Concepts and Theory

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24-2 ICPR4 User’s Manual and Technical Reference, Volume 2

Contents
24. 2D Groundwater, Concepts and Theory ..................................................................................... 5
24.1 Basic Concepts ...................................................................................................................... 5
24.2 Interaction with the Vadose Zone ......................................................................................... 7
24.2.1 Groundwater Interaction with the Green-Ampt Method................................................. 8
24.2.2 Groundwater Interaction with Vertical Layers .............................................................. 11
24.3 Groundwater Interactions with the Surface ......................................................................... 11
24.3.1 Surface Water – Groundwater Interactions with Mapped Basins................................... 14
24.3.2 Surface Water – Groundwater Interactions with Pond Control Volumes ....................... 14
24.3.3 Surface Water – Groundwater Interactions with Channel Control Volumes .................. 15
24.3.4 Surface Water – Groundwater Interactions with 2D Overland Flow Nodes ................... 15
24.4 Groundwater Interaction Below the Confining Layer (Leakage) .......................................... 15

ICPR4 User’s Manual and Technical Reference, Volume 2 24-3

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24-4 ICPR4 User’s Manual and Technical Reference, Volume 2

24. 2D Groundwater, Concepts and Theory

24.1 Basic Concepts
ICPR can be used to model 2D horizontal saturated flow in the surficial aquifer including vertical
leakage across a confining layer and seepage at the ground surface. Like the overland flow module,
the groundwater component uses a flexible triangular mesh as its computational framework.

A finite element approach with a six-point quadratic triangular element as

described by Martínez in the following reference is used as the basis for 2D
groundwater flow in ICPR. Nodes are placed at triangle vertices and at the
midpoints along the triangle sides with this technique.

Martínez, José Bienvenido, 1989, Simulación Matemática de

Cuencas Subterráneas, Flujo Impermanente Bidimensional: Centro
de Investigaciones Hidráulicas, Facultad de Ingeniería Civil,
ISPJAE.

Details of the finite element formulation are provided in Appendix D.

Conceptually, ICPR models saturated horizontal flow in the surficial aquifer system above a confining
layer. Heads (elevations) are calculated at the nodes. Spatially and temporally variable leakage
through the confining layer can be included in the model.

Like 2D overland flow, a triangular computational mesh is formed from graphic elements and then a
honeycomb mesh is derived from the triangles. However, honeycombs are formed not only around
the triangle vertices, but also the mid-nodes as shown below.

ICPR4 User’s Manual and Technical Reference, Volume 2 24-5

The triangle mesh is intersected with porosity zone and conductivity zone map layers to determine
area weighted average porosities and conductivities by triangle. The honeycomb mesh is intersected
with a leakage zone map layer to determine average leakage coefficient values by individual
honeycomb. Triangle nodes (vertices and mid-nodes) are intersected with various DEMs to
determine ground, confining layer, initial water table and potentiometric elevations needed for the
computations.

The 2D groundwater module in ICPR can interact the surface in several ways. Infiltration into the
unsaturated portion of the soil column can move vertically downward and “recharge” the surficial
aquifer. Seepage can flow into the groundwater system from surface water bodies and from surface
water bodies into the groundwater system. For example, a rapidly rising open channel system might

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initially seep from the channel into the adjacent groundwater system, but when water levels in the
channel recede, seepage can flow from the adjacent groundwater system into the channel. Leakage
across a confining layer can also be incorporated into the groundwater computations. These various
interactions are described in detail in the following sections.

24.2 Interaction with the Vadose Zone

The vadose zone is the unsaturated zone located in the soil column between the ground surface and
the water table. As the water table falls and rises, it exposes more or less of the vadose zone. Soil
moisture accounting and water movement in the vadose zone is handled in ICPR with either a single
soil layer approach (unrefined Green-Ampt) or a multi-layer approach (refined Green-Ampt or
vertical layers). Although ICPR allows the curve number method for rainfall excess computations,
the curve number method cannot be used to interact with the groundwater component of ICPR.
Furthermore, the “allow recharge” option must be set to “Yes” or “Groundwater Only” in the Green-
Ampt and vertical layers lookup tables in order for interactions with the groundwater component to
occur. Regardless of the “allow recharge” setting, no recharge occurs below impervious areas.

In addition to using either the Green-Ampt method or vertical layers for rainfall excess computations,
an overland flow region is required to connect surface hydrology to the groundwater module.
Manual basins do not interact with the groundwater module. Mapped basins inside an overland flow
region and 2D overland flow can both interact with the groundwater module.

Triangular meshes are created independently for the

surface drainage system and for the groundwater
flow system, based on characteristics most
important to each system. A set of “honeycombs” is
formed around the vertices of the surface mesh and
a second honeycomb set is formed around the
vertices and mid-nodes of the groundwater mesh.
The surface honeycomb set is then intersected with
the groundwater honeycomb set along with soil and
land cover maps, and for large systems, a rainfall
fishnet. A mosaic of smaller polygons is formed by
this intersection process and becomes the coupling
mechanism between surface and groundwater
systems. These “polygon soil cylinders” include up to seven attributes:

1. surface honeycomb ID
2. groundwater honeycomb ID
3. soil type
4. land cover type
5. crop coefficient type
6. rainfall station
7. ET station

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Rainfall excess is delivered to the surface node associated with the surface honeycomb ID. And,
groundwater recharge is delivered to the groundwater node associated with the groundwater
honeycomb ID. However, groundwater recharge assigned to a groundwater triangle vertex is
redistributed proportionally to the mid-nodes (as of release v4.03.02). We have found that
redistributing to the mid-nodes avoids abrupt spikes at the vertices and fewer instability issues.

The groundwater honeycomb is also intersected with mapped basins. The surface node attribute for
the polygon soil cylinder becomes the 1D node assigned to the corresponding basin instead of the
surface honeycomb ID.

Various lookup tables are used in conjunction with the soil, land cover and crop coefficient attributes
to determine infiltration, evapotranspiration, rainfall excess, unsaturated flow in the soil column, and
recharge to the water table.

24.2.1 Groundwater Interaction with the Green-Ampt Method

Particulars of the Green-Ampt method, including its various parameters, are described in detail in
Section 7.4 and are not be repeated here. This section is focused on the interaction between the
Green-Ampt method and a dynamic water table. The “Allow Recharge” option for the various soil
zones in the Green-Ampt lookup table must be set to either
“Yes” or “Groundwater Only” for the Green-Ampt method to
interact with the groundwater model.

Although the unrefined Green-Ampt method in ICPR is based

on a single soil layer, two sub-layers are formed when ET is in
play and a root zone exists. Soil moisture is tracked separately
in the root zone and the transmission zone and water is
transferred downward from the root zone to the transmission
zone and from the transmission zone to the water table at
rates equal to the unsaturated conductivity of each respective
zone. The Brooks-Corey soil water retention – hydraulic
conductivity relationship is used and expressed as follows:
n
K ( )     r 
 
Ks    r 

where,

 current moisture content by volume fraction

r residual moisture content by volume fraction

 saturated moisture content by volume fraction

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2
n  3

 pore size index

K ( ) unsaturated vertical conductivity at 

Ks saturated vertical conductivity

The recharge rate delivered to the groundwater model for a given water table elevation is the
unsaturated conductivity for the transmission zone multiplied by the sub-polygon area (i.e. the soil
cylinder area). The rate is converted to a volume based on the hydrology computational time
increment, and the volumes are aggregated for all sub-polygons assigned to the same groundwater
node and delivered at the next groundwater computational increment.

As the water table moves up or down, a recharge correction is calculated that reconciles the
difference between the current moisture content as tracked by the Green-Ampt method and the
specified fillable porosity in the groundwater model. The recharge and recharge correction volumes
are aggregated for all sub-polygons assigned to a groundwater node and for each hydrology time
increment within a given groundwater time increment. These volumes are delivered to the
respective groundwater node at the next groundwater time increment.

It is possible to incorporate perched water tables with the Green-Ampt method in conjunction with
the groundwater model. Consider the sketch below where a localized perched water table exists due
to a hard pan layer. If a specific soil zone is set up for hard pan areas, then the “allow recharge” option
for that zone can be set to “No”. If it is set to “No”, then any sub-polygon soil cylinders in that zone
will not interact with the groundwater model directly. Instead, once the soil column becomes
saturated, rainfall excess moves overland for 2D surface models and can then interact with other soil
cylinders that allow recharge.

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If the “Refined” option is selected in the Green-Ampt data form, then the soil column is vertically
discretized into a specified number of cells for the user defined layer thickness. Each cell has the
same soil properties. Once discretized, ICPR uses the vertical layers methodology described in
Section 7.5 and Section 24.2.2.

In general, the “unrefined” Green-Ampt method is used for higher water table
conditions (e.g season high water table within 6 feet of the ground surface) and
the “refined” method is used for deep water table conditions.

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24.2.2 Groundwater Interaction with Vertical Layers

Input parameters for vertical layers are described in Section 7.5. This approach allows the user to
further discretize the soil column into various layers, with each layer having its own set of soil
properties. Each layer is further refined into smaller cells. Fluxes across cells are based on
unsaturated conductivities as described in
Section 7.5. Only unsaturated
conductivities are needed for the
kinematic solution. The recharge rate is
calculated as the flux across the bottom
cell just above the saturated water table.

As the water table moves upward, it

“swallows” cells. If a cell is inundated more
than 75% by the water table, it is merged
with the cell above it and the moisture
content is redistributed accordingly. As
the water table drops, the moisture
content of the newly exposed portion of a
given cell is automatically set to field
capacity. If more than 25% of a given cell is
exposed, it becomes active.

Perched water tables can be modeled like

that described for the Green-Ampt method. But it is also possible to include a hard pan or clay layer
in the vertical discretization and then allow recharge to occur.

24.3 Groundwater Interactions with the Surface

The 2D groundwater regions interact with the 2D overland flow regions (including mapped basins)
that geographically overlap or intersect with one another. Groundwater will also interact with 1D-
elements if they are part of channel control volumes, pond control volumes, and French drains within
a 2D overland flow region. Rating curve and weir links can be attached to a groundwater injection
well and deliver water directly to the groundwater module without an overland flow region. There is
no direct interaction between groundwater and manual basins.

There are two things that must be considered when the water table intercepts the ground surface.
The first is related to storage and the second is related to seepage rates. A change in porosity occurs
above the ground surface which affects storage characteristics. Fillable porosity lookup tables are
discussed in Section 7.3. A distinction is made in that lookup table between above ground porosity
and below ground porosity. If the water table intercepts the ground surface at a surface node that is
inundated (e.g. a lake), that groundwater node is converted to a known head condition with its head
dictated by the surface node. The above ground porosity is used at that node. Once all known head

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nodes have been set, an area weighted average porosity is calculated for each triangle before
proceeding with the groundwater computations. The weightings are set to 1/12 th for the vertices and
3/12th for the mid-nodes. It is possible to have some nodes above the ground and others below the
ground for a given triangle, and that is factored into the averaging.

The implication of the

area weighted averaging
of porosities should be
understood. Consider the
figure shown to the right.
A pond is located on the
right side of the figure
(shaded blue) and all
groundwater nodes in the
pond automatically
become known heads.
The triangle formed by
vertices 168, 194 and 196
has an edge in the pond.
Consequently, nodes 168, 177 and 196 are considered known heads and the above ground porosity
is used for those nodes when computing the weighted average porosity for triangle 168-194-196. A
total of 5/12th of the above ground porosity is applied to the triangle although only a small fraction
of it is inundated.

A more accurate representation of the storage can be obtained by refining the mesh along the edge
of the pond like that shown below. Notice how smaller triangles straddle the edge of the pond (dark
blue line). The penalty for the increased accuracy is a more complex groundwater model and the
associated extra computational effort. As the modeler, you must decide if the extra accuracy is
warranted. A similar situation occurs along open channels.

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Seepage as related to ICPR is the direct exchange of water between the groundwater system and the
surface system without passing through the vadose zone. Two primary types of seepage are
calculated and tracked by ICPR:

1. seepage at a known head groundwater node; and,

2. seepage at an unknown head groundwater node.

The first type, seepage at a known head node, occurs at all user specified boundary stage nodes. But,
it can also occur when the water table is above the ground surface and the corresponding surface
node is inundated. For example, if a groundwater node coincides with a lake, then that groundwater
node is forced to a known head condition and the elevation is dictated by the lake. Seepage rates
are calculated as described in Section D.7 and Equation D.31. In terms of mass balance, the “above
ground” porosity is factored in for that portion of the water table above the ground surface.

The second type, seepage at an unknown head groundwater node, typically occurs along a sloping
ground surface like a river bank or a seepage face on a hill. In these cases, the groundwater model
calculates a water table elevation above the ground as if it were still in the soil column, even though
there is nothing on the surface to physically support that elevation. In other words, the water flows
overland to another location farther downstream and does not pond on the surface. In this situation,
ICPR pulls the groundwater elevation down to the ground surface and simultaneously sends a volume
of water to the corresponding surface node equal to the honeycomb area multiplied by the depth
above the ground and the average “below ground” porosity of the honeycomb. The following
seepage rate is applied to the corresponding surface node for a full groundwater time increment.

ICPR4 User’s Manual and Technical Reference, Volume 2 24-13

QSeepage   h1  h2   ( A)    / dt gw

where,

QSeepage is the seepage rate (f3s-1, m3s-1)

h1 is the calculated water table elevation (f, m)

h2 is the ground surface elevation at the groundwater node (f, m)

A is the GW honeycomb surface area (f2, m2)

 is the below ground fillable porosity

dt gw is the groundwater computational time increment (s)

ICPR also tracks “undelivered” seepage. This can occur for both seepage types described above if
the groundwater node is located outside of an overland flow region. It can also occur when the user
specifies a known head condition within an overland flow region, but below the ground surface.

24.3.1 Surface Water – Groundwater Interactions with Mapped Basins

Mapped basins use traditional hydrology (e.g. the NRCS unit hydrograph method) but are
incorporated in the overland flow region and consequently, can interact with the groundwater
module. As you might recall, overland flow triangles and honeycombs are removed from mapped
basins. Therefore, the groundwater honeycomb is intersected directly with the mapped basins and
soils, impervious, etc. map layers, forming a system of sub-polygons. Each sub-polygon has a
groundwater node ID and a surface node ID. The surface node is the same as the 1D node for the
mapped basin. Recharge is delivered to the groundwater node and rainfall excess is delivered to the
surface node.

When the groundwater table exceeds the ground surface, seepage is calculated as described in the
previous section and sent directly to the surface node. The groundwater elevation at that node is
pulled back down to the ground surface elevation. Groundwater never exceeds the ground surface
inside a mapped basin.

24.3.2 Surface Water – Groundwater Interactions with Pond Control Volumes

Pond control volumes are graphic elements placed inside the overland flow region boundary. They
are referenced to a 1D node and are treated as level pools. The surface honeycomb is propagated
inside the pond control volume and is intersected with the groundwater honeycomb. When a specific
honeycomb inside a pond control volume is dry, vertical unsaturated flow can occur and recharge is
delivered to the corresponding groundwater node. When the groundwater table exceeds the ground
surface, seepage is sent to or pulled from the 1D node corresponding to the pond control volume
depending on the head differential. A known head condition is applied to the corresponding

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groundwater node when the soil column is saturated and the surface is inundated. The known head
condition is based on the level pool surface water elevation.

24.3.3 Surface Water – Groundwater Interactions with Channel Control Volumes

Like pond control volumes, channel control volumes are graphic elements placed inside the overland
flow region boundary and are referenced to a 1D surface node. Recharge and seepage works like that
in a pond control volume. However, the water surface is not flat inside a channel control volume.
When the soil column is saturated and the ground surface is inundated at a honeycomb, a known
head condition is applied to the corresponding groundwater node. The know head condition is based
on a sloping water surface interpolated between 1D nodes.

24.3.4 Surface Water – Groundwater Interactions with 2D Overland Flow Nodes

2D overland flow nodes are treated like 2D nodes inside pond and channel control volumes in terms
of recharge and seepage. However, when the soil column is saturated and the ground surface is
inundated at a 2D node, a known head condition is applied to the corresponding groundwater node
based on the 2D surface node water surface elevation.

24.4 Groundwater Interaction Below the Confining Layer (Leakage)

Leakage can occur through a confining layer
that separates the surficial (phreatic) aquifer
from a pressurized confined aquifer system.
There are three options in ICPR relative to
leakage:

1. no leakage
2. leakage based on a leakance value
3. leakage based on Darcy’s equation

The bottom of the confining layer is not required

for options 1 and 2, but is required for option 3.
The leakage rate for option 2 is calculated as
follows:

QLeakage  ( L)   h1  h2   ( A)

where,

QLeakage is the leakage rate (f3s-1, m3s-1)

L is a leakance value expressed as a flow rate (f3s-1, m3s-1) per foot (meter) of head per
unit area (f2, m2). The units for the leakage value become “per second” (s-1).

ICPR4 User’s Manual and Technical Reference, Volume 2 24-15

h1 , h2 are the water table and potentiometric elevations, respectively (f, m). If the
potentiometric elevation drops below the top of the confining layer, then h2 is set to
the top of the confining layer

A is the GW honeycomb surface area (f2, m2)

Darcy’s equation is used for option 3 and is written as follows:

h  h  
QLeakage  ( K )   1 2   ( A)
 t 

where,

K is the confining layer saturated vertical conductivity (fs-1, ms-1)

t is the confining layer thickness (f, m)

24-16 ICPR4 User’s Manual and Technical Reference, Volume 2

September 2017

© 2017, All Rights Reserved

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
25. Groundwater Regions

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25-2 ICPR4 User’s Manual and Technical Reference, Volume 2

Contents
25. Groundwater Regions................................................................................................................. 5
25.1 Creating a Groundwater Region ............................................................................................ 5
25.1.1 Create and Draw Region in ICPR ..................................................................................... 5
25.1.2 Importing a Groundwater Region ................................................................................... 7
25.2 Groundwater Region Manager .............................................................................................. 7
25.2.1 Surface DEMs ................................................................................................................. 9
25.2.2 Map Layers ................................................................................................................... 11

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25-4 ICPR4 User’s Manual and Technical Reference, Volume 2

25. Groundwater Regions

Like overland flow regions, at least one groundwater region must be created to model 2D
groundwater flow. Groundwater regions can be aligned with overland flow regions, but that is not a
strict requirement of ICPR and quite often groundwater regions extend beyond the limits of overland
flow regions. Furthermore, it is possible to create a groundwater model without creating an overland
flow region and vice versa.

ICPR does include parallel processing and surface hydrology and routing have been optimized to take
advantage of multi-core processors. The groundwater module on the other hand is finite element
based which does not lend itself directly to parallel processing. Decomposition of the mesh into
smaller meshes would be required and this is not done automatically (as of this writing) in the
program. However, it is possible to create multiple independent groundwater regions within a given
project and ICPR will process these regions simultaneously if a multi-core processor is available and
invoked at simulation time. For example, two separate groundwater regions might be created with
a common edge along the centerline of a river. Both regions would interact with the river and share
the same boundary condition, but they would otherwise be independent of one another. ICPR would
process the two regions simultaneously if multiple processors are available, thus greatly speeding up
the calculations.

25.1 Creating a Groundwater Region

There are two primary ways to create a groundwater region. The first is to draw it in ICPR and the
second is to import a shapefile, a DXF file or a CSV file. Regardless of the method used, you must
work in the Graphic View. Also, it is critical to have your coordinate/projection system established
ahead of time. Mesh building and parameterization depend on geo-referencing and all geo-
referenced information must be on the same projection system at the time of importation. ICPR has
no means of changing coordinate systems once data has been entered or imported. And, ICPR
cannot work with multiple projection systems within a given project.

25.1.1 Create and Draw Region in ICPR

Typically, if you are going to create a region in ICPR, you will need either a background image or a
DEM to guide you. Background images are discussed in Chapter 5. The Surface Manager is
discussed in detail in Chapter 9. DEMs, as they relate to groundwater flow, are discussed in Section
25.2.1.

To create a region, click the “Create Groundwater Region” icon at

the top of the graphic view window as shown to the right. If the
autoname feature is turned off, you will be prompted for a region
name. Otherwise, the region will be automatically named and a prompt will appear at the bottom
of the graphic view window as shown below. You can begin drawing, or there are various snap
options. For example, if you press “G” and then move the cursor over the grid and left click, a point
will be placed at the nearest grid intersection. “S”, “N” and “M” allow you to snap to existing map
features. A “P” will allow you to enter exact coordinates and a “T” allows you to trace along an

ICPR4 User’s Manual and Technical Reference, Volume 2 25-5

existing polyline. If you would like a groundwater region to exactly match an overland flow region,
you can press the “X” and then simply click on the overland flow region to copy the entire polygon.
“O” allows you to draw a geometric shape such as a circle or rectangle.

An example groundwater region is shown below. A tree structure exists on the left side of the general
tab that allows you to toggle various graphic elements on and off. Graphic elements associated with
groundwater regions are outlined with a red rectangle. Notice the name “GWR-001” appears directly
below “Groundwater Regions” in the tree structure. The region boundary can be toggled on and off
by checking the box next to shape, directly below “GWR-001”.

There are several ways to delete a region, but you should be

extremely careful because not only will the region graphic be
deleted, but all data and features assigned to a region will also be
deleted. The “Delete Single” icon shown to the right allows you to
pick a specific feature or graphic element to delete.

If you need to make a change to the region boundary, it is better to

use the “Edit Polyline” icon shown to the left rather than deleting it
first and creating a new one.

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25.1.2 Importing a Groundwater Region

It is often convenient to import a region
boundary that was created in GIS or CAD.
This can be done by right-clicking on
“Groundwater Regions” in the data tree
structure of the general tab as shown to the
right. You can import either a shapefile, a
DXF file of a CSV file.

Here are some important things to keep in

mind when importing regions from other
sources:

1. You should use as few points as

possible to define the region
boundary without compromising
accuracy.
2. If you are using ArcGIS generated shapefiles, make sure you are exporting the file
with a consistent projection system if you haven’t defined a CRS for the ICPR
project. If you have defined a CRS, then ICPR will utilize the projection file that
accompanies the shapefile to translate it into the ICPR CRS.
3. The shape file should be a polygon type and accompanied by a dbf file with a name
field. Also, you should explode multi-part features.
4. For DXF files, use the AutoCAD R12 format. You will need to know the layer names
for line work and text. ICPR can handle only lines and closed polylines for polygons.
Make sure that the region boundary is a closed polygon – i.e. snap the ends.

Vertical walls are assumed around the perimeter of the region boundary unless other
provisions are made (e.g. incorporate a boundary stage line graphic element along a portion
of the region boundary).

25.2 Groundwater Region Manager

The groundwater region manager is used to assign the various
map layers and DEMs to the region needed for final
parameterization. It is accessed by clicking “Regions >
Groundwater Region Manager” as shown to the right. A partial
view of the form appears on the following page.

You cannot create a new region inside the manager. Regions can only be created graphically in ICPR
in the graphic view form or by importing a region boundary from a shapefile or a DXF file as previously
described. You can, however, delete a region by clicking the delete button at the bottom of the form.
Once again, if you delete a region, you simultaneously delete all data associated with it. So be very
careful with the delete button.

ICPR4 User’s Manual and Technical Reference, Volume 2 25-7

The name of the region can be changed in the region manager, but the scenario it resides in cannot
be changed. The minimum triangulation angle affects the shape and number of triangles. In general,
as the angle increases, so do the number of triangles. Although a minimum angle of about 21 degrees
is optimal in terms of minimizing the number of triangles, a 45-degree or 60-degree minimum
provides better shaped triangles.

ICPR goes through a triangle refinement process using the Delaunay method of triangulation to meet
the minimum angle constraint. If left unconstrained, situations can occur where thousands of tiny
triangles are created to satisfy the minimum angle criteria. Consequently, a second constraint is used
to stop the refinement process. If, during the refinement process, a triangle area drops below a
specified minimum triangulation area, then the refinement process stops. A minimum triangulation
area of 150 square feet works well in most cases.

A preliminary triangle mesh can be constructed by clicking the “Preprocess” button at the lower-left
corner of the region manager form. This is useful for evaluating triangle densities based on map
features prior to execution of the simulation.

A tool is available to help in your evaluation of the preliminary triangular mesh in the “Search” tab of
the graphic view as previously discussed in Section 20.2.

After the groundwater honeycomb mesh has been created, it is automatically rasterized for
subsequent polygon processing with other map layers. The cell size data field establishes the pixel
size for this rasterization process. In general, it should be a relatively small number such as 1 foot as
shown. But larger cell sizes might be needed for larger projects due to memory issues. Just keep in

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mind that these cell sizes must be even multiples of polygon map layer cell sizes (discussed in
Sections 8.2.3) and cell sizes specified in the overland flow region manager (see Section 20.2).
For example, if the cell size for a conductivity zones polygon map layer is set to 4 feet, then the
honeycomb cell size would have to be 0.25, 0.5, 1, 2 or 4. Honeycomb cell sizes should be less than
or equal to other map layer cell sizes.

25.2.1 Surface DEMs

There are multiple surfaces (DEMs) that can be set in the region manager such as the ground surface,
the initial water table surface, the top of the confining layer, etc. A discussion of DEMs and surfaces
as specifically related to groundwater flow is presented below.

It is possible to use a single elevation for either the ground surface, initial water table surface or any
of the other surfaces used in groundwater modeling by checking the appropriate box and typing in
an elevation. This is convenient for small projects or for testing hypothetical situations or specific
features of the program.

All surfaces are DEMs that must be imported via the Surface Manager.

As mentioned in the previous section, there are three surfaces that are always required for
groundwater modeling: (1) the ground surface; (2) the top of the confining layer (the base of the
surficial aquifer); and, (3) the initial water table. A single elevation or flat surface can be specified for
any or these surfaces, or a separate DEM can be specified for each. Optional surfaces include the
bottom of the confining layer and time-dependent potentiometric surfaces. Creating and importing
surfaces is described in detail in Chapter 9 and will not be repeated here. Also, creating a DEM from
a contour map layer is described in Section 8.4.

An important concept to understand is the interface between the surface water system and the
groundwater system. Section 24.3 describes how ICPR handles the interactions between these two
systems. When lakes, ponds, rivers and other water bodies are involved, the ground surface must
follow the bathymetry (bottom) of the water body. It is not appropriate to simply project the ground
surface across the water surface. For example, LiDAR technology does not work well below water
surfaces so some post-processing is necessary to fit bathometry into the final DEM.

25.2.1.1 Ground Surface (required)

Purpose: The ground surface is used to set ground elevations at triangle vertices and mid-nodes.
Ground elevations become the interface location between the surface and groundwater models and
are needed to determine when and how much seepage into (or out of) the surface drainage system
occurs.

It is possible to use a single ground elevation (i.e.

a flat ground surface) by checking the box as
shown above and typing the elevation to be used. In this example, the ground surface elevation for
the entire region is set to 100.

ICPR4 User’s Manual and Technical Reference, Volume 2 25-9

25.2.1.2 Initial Water Table Surface (required)

Purpose: The initial water table surface is used to initialize water table elevations at vertices and mid-
nodes.

It is possible to use a single initial water table

elevation (i.e. a flat water table surface) by
checking the box as shown above and specifying the elevation to be used.

25.2.1.3 Confining Layer Top Surface (required)

Purpose: The confining layer top surface forms the base or bottom of the surficial aquifer. It is often
referred to as the “aquifer base”. The thickness of the surficial aquifer at any point in time is the
distance between the water table elevation and the top of the confining layer. Multiplying this
thickness by the horizontal conductivity yields the transmissivity, which is variable for phreatic
aquifer systems.

It is possible to use a single elevation for the top

of the confining layer by checking the box as
shown above and providing the elevation to be used.

25.2.1.4 Confining Layer Bottom Surface (optional)

Purpose: As described in Section 24.4, leakage through the confining layer can be included in the
groundwater model. There are two options for calculating the leakage. One of those options uses
Darcy’s equation and requires that the thickness of the confining layer be known at all vertices and
mid-nodes. In ICPR, the thickness is calculated by subtracting the bottom of the confining layer from
the top of the confining layer. Consequently, a confining layer bottom surface is required if the Darcy
equation option (i.e. “Leakage with Confining Layer”) is selected as the method for leakage
calculations.

It is possible to use a single elevation for the

bottom of the confining layer by checking the box
as shown above and providing the elevation to be used.

25.2.1.5 Potentiometric Surfaces (optional)

Purpose: Whenever leakage is to be included in the groundwater model, the potentiometric pressure
below the confining layer is used as a boundary condition. This can be specified as a table of time-
elevation pairs that is applied uniformly over the entire groundwater region. Or, the potentiometric
levels can be varied both spatially and temporally by using DEMs at various points in time.

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The “Use Surfaces with Offsets” option requires that a DEM be specified for various time increments
over the simulation period like that shown below. A single DEM can also be used repeatedly with
time-variable vertical offsets. At least two points in time must be included in the table and cover the
entire simulation period.

25.2.2 Map Layers

A lengthy discussion of the Map Layer Manager is provided in Chapter 8. This section focuses on
the three map layers used in conjunction with lookup tables to set certain groundwater properties
including fillable porosity, saturated horizontal conductivity and vertical leakage properties. The
various map layers form “zones” that work in conjunction with lookup tables. The fillable porosity
zones and the conductivity zones are superimposed with the triangular groundwater mesh to
determine area weighted averages by triangle. The leakage zones are superimposed with the
groundwater honeycomb mesh to determine area weighted averages by honeycomb.

It is helpful to understand how each parameter affects groundwater movement before establishing
the various map layers and zones. Fillable porosity is a storage component and affects the magnitude
of vertical fluctuations in the water table. The higher the porosity, the more storage there is and the
smaller the vertical fluctuations with all else being equal. As the porosity decreases, the storage also
decreases and causes vertical fluctuations to increase. Conductivity affects the transmissivity and
consequently, the horizontal movement of groundwater. Groundwater moves faster as
conductivities increase in value.

ICPR4 User’s Manual and Technical Reference, Volume 2 25-11

There are several strategies that can be used in

establishing the mapping zones needed for
groundwater properties and as the modeler, you
must decide what works best for your application.
Although it is possible to use three separate map
layers to establish porosity, conductivity and
leakage zones, it is equally possible to create a
single map layer and use it for all three
groundwater properties. In the example shown to
the right, Thiessen polygons have been created
around a network of groundwater observation
wells (red X’s) allowing the various groundwater
properties to be adjusted by well during the
calibration process. High leakage is expected
below the lake, so four additional zones were
established there to allow refinement of leakage
parameters.

Although the fillable porosity above ground should typically be set to 1.0, there are some situations
when it should be set to something other than 1.0. For example, an exfiltration trench consists of a
perforated pipe in a gravel envelope. The ground surface for modeling purposes would be the
bottom of the trench, so as the water table intercepts the bottom of the trench, the porosity would
change from that of the native soil (e.g. 0.15) to that of the gravel (e.g. 0.5). A fillable porosity zone
would be needed for the extents of the trench to affect the porosity differences.

25.2.2.1 Fillable Porosity Zones (required)

Purpose: Intersects the groundwater triangular mesh to determine area weighted averages of below
ground and above ground fillable porosities by triangle. Once the average porosities for the triangles
are determined, area weighted averages are calculated for each honeycomb formed around vertices
and mid-nodes. Both sets are used throughout a given simulation.

It is possible to use a single porosity zone by

checking the box as shown above and typing
the name of the zone to be included in the model. In this example, the zone “Porosity” must be
included in the appropriate fillable porosity lookup table.

Corresponding Lookup Table: Fillable Porosity Sets. Refer to Section 7.3 for details on the lookup
table associated with fillable porosity.

25-12 ICPR4 User’s Manual and Technical Reference, Volume 2

25.2.2.2 Conductivity Zones (required)

Purpose Intersects the groundwater triangular mesh to determine area weighted averages of
saturated horizontal conductivity by triangle.

It is possible to use a single conductivity

zone by checking the box as shown above
and typing the name of the zone to be included in the model. In this example, the zone
“Conductivity” must be included in the appropriate conductivity lookup table.

Corresponding Lookup Table(s): Conductivity Sets. Refer to Section 7.3 for lookup tables
associated with conductivity data.

25.2.2.3 Leakage Zones (optional)

Purpose: Intersects the groundwater honeycomb mesh to determine area weighted averages of
leakage parameters by groundwater honeycomb if the leakage option is invoked.

It is possible to use a single leakage zone by

checking the box as shown above and providing
the zone name to be used.

ICPR4 User’s Manual and Technical Reference, Volume 2 25-13

Corresponding Lookup Table(s): Leakage Sets. Refer to Section 7.3 for lookup tables associated
with leakage data.

25-14 ICPR4 User’s Manual and Technical Reference, Volume 2

©2017, Streamline Technologies, Inc.
User’s Manual and Technical Reference
Volume 2, Chapter 26
Groundwater Graphic Elements

September 2017

© 2017, All Rights Reserved

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
26. Groundwater Graphic Elements

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26-2 ICPR4 User’s Manual and Technical Reference, Volume 2

Contents
26. Groundwater Graphic Elements ................................................................................................. 5
26.1 Exclusion ............................................................................................................................... 6
26.2 Breakpoint ............................................................................................................................ 7
26.3 Breakline ............................................................................................................................... 7
26.4 Drains (Point, Line, Area) ...................................................................................................... 8
26.5 Irrigation Wells ...................................................................................................................... 9
26.6 Injection Wells....................................................................................................................... 9
26.7 Boundary Stage (Point, Line, Area) ..................................................................................... 11
26.8 External Hydrograph (Point, Line, Area).............................................................................. 12

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26-4 ICPR4 User’s Manual and Technical Reference, Volume 2

26. Groundwater Graphic Elements

Groundwater graphic elements are used as the basis for mesh construction. The list of graphic
elements below the ground is not as extensive as above the ground. Elements include exclusions,
breakpoints and breaklines, drains, irrigation wells and injection wells, along with various features
for establishing boundary conditions.

The following sketch is taken from ICPR’s graphic view editor and depicts the options specifically
related to 2D groundwater flow. Groundwater regions were discussed in detail in Chapter 25. As
mentioned in that chapter, it is possible to have multiple regions for a given project. Graphic
elements are always placed in the active region of the active scenario.

To add any of the above graphic elements to your project, select one from the dropdown list and then
click the “create graphic element” icon. A prompt will appear at the lower left corner of the graphic
view window with drawing instructions.

It is possible to create all the 2D groundwater features in a GIS and then import them to ICPR via an
XML file or a collection of CSV files or shapefiles. To import a shapefile, expand the “Feature Types”
of graphic element tree located on the left side of the “general” tab as shown below. Move the cursor
over any of the features and right click.

ICPR4 User’s Manual and Technical Reference, Volume 2 26-5

Data forms for any of the graphic elements can be opened by double clicking it, or using the “2D
Features > Groundwater” menu options.

26.1 Exclusion
Exclusions are closed polygons within a groundwater region. The area inside this type of feature is
“excluded” from the triangular mesh generation process. Consequently, groundwater cannot move
across an exclusion polygon. Groundwater flow is permitted along its perimeter. Exclusions can be
used to incorporate fully penetrating impermeable barriers within the groundwater region, such as a
sub-surface wall (see figure below).

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26.2 Breakpoint
Breakpoints are added for refinement of the triangular mesh, like overland flow breakpoints, and can
be placed anywhere within a groundwater region. However, breakpoints placed in an exclusion
feature are ignored. Vertices are guaranteed at breakpoints.

An example is shown below with breakpoints (red

markers) placed at strategic locations in a ditch as
well as upland areas near the ditch. It is important
to understand that mid-nodes are automatically set
along the triangle edges. Notice that although
breakpoints are placed in the ditch, the triangle
edges sometimes fall outside of the ditch and
consequently, the corresponding mid-nodes also
fall outside the ditch. This type of placement
impacts both seepage and recharge rates. The
water table must exceed the ground elevation at
specific vertices and mid-nodes for seepage to
occur.

The approach illustrated in the example above is probably adequate for a regional model, but more
detail and more accuracy in terms of seepage and recharge might be warranted for a site-specific
application. As discussed in the following
section, breaklines can be used to insure
precise locations of triangle edges.

Uniform patterns of breakpoints can be placed

by pressing “Z” after clicking the “Create
Graphic Element” icon when the breakpoint
graphic element is active. Either a square
pattern or equal triangle sides can be used to
create the breakpoints. The breakpoint pattern
can be limited to an “active fence” by checking
the box shown to the right. An entity buffer
can also be specified as shown, that is used as a
minimum distance between a breakpoint and
any other visible entity.

26.3 Breakline
Breaklines, like breakpoints, are used to refine
the triangular mesh. Triangle vertices are
guaranteed at each coordinate point of the breakline. Furthermore, triangle edges are guaranteed
along the breakline.

ICPR4 User’s Manual and Technical Reference, Volume 2 26-7

The example shown to the right is

an enlargement of the area
discussed in the previous section.
Breaklines (the red lines) are used
along the bottom of the ditches
and near the top of bank. Notice
how triangle edges follow the flow
line of the ditches. Mid-nodes
along these edges also fall inside
the ditch. Also notice how the
honeycombs fall along the
bottom of the ditch for the most
part. This is where most of the
seepage will occur and is a much
more accurate representation of
the groundwater – surface water
interface. However, the
additional accuracy comes at a substantially higher computational price. It might not be practical
to include this much detail in a regional model.

26.4 Drains (Point, Line, Area)

Groundwater drains can be used to control water table elevations such as tile drains in an
agricultural application or roadway underdrains. They can be placed as either points, lines or areas.
The vertical alignment is set as either a depth below ground or at an elevation. For drain lines, a
depth/elevation must be placed at both
ends of the line with the first value set at
the beginning of the line and the second
at the end of the line. A surface 1D node
or a 1D/2D node interface point must be
specified to receive any groundwater
flow through the drain. For example,
drain “GWDLN-0001” shown to the right
drains into node “NTZ-0010”. From an
accounting perspective, the water shows
up as seepage for the 1D surface node
and external flow for the groundwater node.

The flow to a drain is head dependent based on a user specified conductance. The units for the
conductance value depend on the drain type and are summarized as follows:

1. Drain Point – cubic feet per second per foot of head or square feet per second

26-8 ICPR4 User’s Manual and Technical Reference, Volume 2

2. Drain Line – cubic feet per second per foot of head per lineal foot of drain or
feet per second
3. Drain Area – cubic feet per second per foot of head per square foot of drain area
or per second
4. Meters replace feet for metric units of the above.

The maximum possible flow rate is restricted by the limiting head. Note that the head is measured
as the groundwater elevation minus the elevation of the receiving 1D node or the bottom of the drain,
whichever is higher. Flow reversals are possible with drains.

The groundwater elevation can drop below the drain.

26.5 Irrigation Wells

As explained in Section 7.8.2, irrigation water can be pulled from a well in the surficial aquifer. The
well name is specified in the crop coefficient table and must match the irrigation well name. Once
the well feature is graphically placed, the vertical alignment must be specified. This is done by
opening the irrigation well data form and selecting the vertical placement option you wish to use and
typing in the depth / elevation value.

The Depth / Elevation must not project below the top of the confining layer.

26.6 Injection Wells

1D weir links and 1D rating curve links can be attached “to” a groundwater injection well. This is the
only way to connect a 1D component directly to the groundwater module without an overland flow
region. An example is shown below where a rating curve link is connected “from” a stage / area node
and “to” a groundwater injection well. Water injected to the groundwater module appears as external
flow in the water budget. See Section 27.4 for additional information on French Drain and Injection
Well strategies.

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There are three parameters that must be set for the injection well as shown below: (1) well diameter;
(2) mesh scaling factor; and, (3) shut off elevation.

The scaling factor is used by ICPR to build the triangular computational mesh around the injection
well. Two internal breaklines are created when a “Scenario > Build” takes place (mesh construction
and parameterization). The first breakline is circular with 10-degree chord segments placed a
distance equal to the well diameter times the mesh scaling factor away from the center of the well.
The second breakline is placed 2 times this distance away from the first breakline. For example, given
a well diameter of 2 feet and a mesh scaling factor of 2, the first breakline is placed at a radius of 4
feet away from the center on the well. The second breakline is placed 8 feet away from the first
corresponding to a radius of 12 feet from the center of the well. The corresponding mesh
construction is shown below.

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26.7 Boundary Stage (Point, Line, Area)

A “no flow” boundary condition (i.e. vertical wall) is assumed along the region boundary unless a
known head condition is specified. Known heads can be set anywhere inside or along the edges of a
groundwater region by using the boundary stage feature. These can be specified at a single point,
along a continuous line or across an area defined by a closed polygon.

Once you have placed the boundary stage point, line or area, you need to identify the table name(s)
that contains the time-stage data (a boundary stage table). This is done by opening the respective
data form and filling out the boundary stage name(s) as shown below.

For the boundary stage line feature, linear interpolation based on distance is used between the two
endpoints. It is important that the first table correspond to the first point entered on the boundary
stage line and the second table correspond to the last point. This can be determined by using the
edit polyline tool. Click the edit polyline icon then click the boundary line feature. The points are
numbered in the order that they were entered.

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26.8 External Hydrograph (Point, Line, Area)

Water can be added or withdrawn anywhere inside or along the edges of a groundwater region by
using the external hydrograph feature. These can be specified at a single point, along a continuous
line or across an area defined by a closed polygon. A positive flow rate adds water to the groundwater
system and a negative value withdraws it.

Once you have placed the external hydrograph point, line or area, you need to identify the table
name(s) that contains the time-flow data (an external hydrograph table). This is done by opening
the data form and filling out the external hydrograph name as shown below.

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The data form is the same for the three external hydrograph types. Each of them requires a single
table name and a “Proportion of Total Flow” expressed as a decimal value from zero to one. For
example, if the proportion of total flow is set to 0.75, then 75% of the flows in the corresponding
external hydrograph table would be delivered to the groundwater system. The flow is further
distributed based on proportional length for the line feature and proportional area for area features.

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26-14 ICPR4 User’s Manual and Technical Reference, Volume 2

September 2017

© 2017, All Rights Reserved

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
27. Groundwater Examples

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Contents
27. Groundwater Examples .............................................................................................................. 5
27.1 Example 1 – Pond Drawdown, Sloping Water Table ............................................................... 5
27.1.1 Base Data ........................................................................................................................ 6
27.1.2 Model Setup.................................................................................................................. 11
27.1.3 Mesh Construction ........................................................................................................ 15
27.1.4 Simulations and Results ................................................................................................ 16
27.2 Example 2 – Infiltration Galleries ......................................................................................... 24
27.2.1 Background................................................................................................................... 24
27.2.2 Model Setup ................................................................................................................. 27
27.2.3 Computational Meshes ................................................................................................. 34
27.2.4 Simulation Control........................................................................................................ 35
27.2.5 Analysis ........................................................................................................................ 36
27.3 Example – Injection Well ...................................................................................................... 40
27.3.1 Groundwater Region ..................................................................................................... 40
27.3.2 Injection Well and Breaklines ........................................................................................ 41
27.3.3 Boundary Stage Line ..................................................................................................... 42
27.3.4 Groundwater Properties ............................................................................................... 44
27.3.5 Groundwater Region Manager ...................................................................................... 44
27.3.6 Analysis......................................................................................................................... 45
27.4 French Drain and Injection Well Strategies .......................................................................... 49
27.4.1 French Drains ................................................................................................................ 49
27.4.2 Drain Wells ................................................................................................................... 53

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27. Groundwater Examples

Three example applications are presented in this chapter that incorporate 2D groundwater. Although
the data for these applications are included in the example data sets, the computational meshes and
results are not included to minimize download sizes. You will have to construct the meshes (Scenario
> Build) and run the simulation to view the results. Section 27.4 includes a lengthy discussion on
French drain and injection well strategies.

27.1 Example 1 – Pond Drawdown, Sloping Water Table

This example is in the Clearwater area of Pinellas County, Florida.
The modeled area is 62.2 acres in size as shown to the right.
However, the focus is on the drainage and stormwater
management system for the Regency Oaks Retirement
Community. Most of the infrastructure data was obtained from
the Southwest Florida Water Management District (SWFWMD)
permit records. However, some modifications to that data were
made for illustrative purposes of this example and results
presented here should not be used for design or flood
management purposes. (Note: This example is also presented in
Section 14.4, but without groundwater considerations.)

There are three stormwater ponds and although each of them

has an outfall, full storage recovery, as modeled in this example,
depends on percolation.

Elevations range from about 90 ft (NAVD 1988) at the north end of the project to about elevation 60
ft (NAVD 1988) at the southwest end. The water table generally slopes with the ground surface with
seepage outcrops along a wetland slough located along the western and southern boundaries of the
project area. All data for this example has already been entered. These key aspects are discussed in
the following sections.

1. Base Data
a. aerial background image
b. surface DEMs
c. thematic polygon map layers
d. lookup tables
2. Model Setup
a. 1D nodal network
b. 2D overland flow
c. 2D groundwater
3. Mesh Construction
a. overland flow region manager
b. groundwater region manager
c. scenario build
4. Simulations and Results

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Begin by opening the following project:

27.1.1 Base Data

Open the Graphic View, maximize it and then click the
zoom extents icon. Uncheck “Scenario1” on the data
tree.

27.1.1.1 Aerial Background Image

A single aerial background image was imported to the
project. Toggle on the background image named “aerial”
as shown below.

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27.1.1.2 Surface DEMs

Three surface DEMs were imported to the project: (1) ground surface; (2) aquifer base; and, (3) initial
water table. These were imported in the surface manager.

Surface “ground” is a LiDAR-based DEM (5x5-foot grid) obtained from the SWFWMD. Surface
“aquifer_base” is the top of the confining layer and was derived from data downloaded from the
Florida Geological Survey. Surface “wt_initial” is the initial water table and was developed by running
an ICPR groundwater model for the area over an extended period until the water table reached near-
equilibrium conditions.

The three surfaces can be view on the raster panel of the Graphic View. These are shown below at an
opacity of 75% and superimposed with the aerial background image. Notice that the aquifer base and
the initial water table are undulating. Percolation from the ponds in this example would be difficult
with the percolation links. The 2D groundwater approach allows for non-flat surfaces and non-
homogeneous soils.

Ground Surface Aquifer Base Initial Water Table

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27.1.1.3 Thematic Polygon Map Layers

Three polygon map layers are used for this example: (1) basins; (2) land use/land cover; and, (3) soils.
Map layers begin as vectors and are then rasterized in the Map Layer Manager.

The “Soils” map layer was downloaded from the NRCS soils web service. The “LandCover” map layer
was originally obtained from the SWFWMD but was modified to better reflect impervious and
pervious areas in the Regency Oaks development. The “Basins” map layer was drawn inside ICPR4.
The raster versions of these 3 map layers are shown below.

Basins LandCover Soils

27.1.1.4 Lookup Tables

Green-Ampt Parameters: Parameters for the Green-Ampt lookup
table were derived from the NRCS SSURGO data using the
procedures and equations described in Section 7.4 of this
manual. The saturated vertical conductivities are set to 50% of the
weighted SSURGO values for a factor of safety (FOS) equal to 2.

The “Refined” method is used in this example which assumes a

homogeneous soil, but discretizes the soil column into smaller cells.
This method is typically used for deep water table conditions and

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more accurately accounts for travel time through the vadose zone to the saturated zone. Soil
moisture and unsaturated vertical conductivity is tracked for each cell throughout the simulation.
The soil layer thickness is set to 20 feet and 100 cells is specified – each cell is 0.2 feet thick. The initial
water table “WT Initial” is set to 999 feet, but it is replaced by the actual water table depth as
determined by the groundwater model. A partial excerpt of the Green-Ampt table is shown below.

Note that the curve number method cannot communicate with the groundwater module in ICPR4.

Impervious Percentages: Impervious and DCIA percentages were set for each “LandCover” zone. The
impervious lookup table for this example is shown below.

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Fillable Porosity: Fillable porosity values are set for each soil zone. Below ground porosities were
calculated as the difference between the Green-Ampt saturated moisture content and field capacity
moisture content. Above ground porosities were set to 1. An excerpt of the fillable porosity table is
shown below.

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Saturated Horizontal Conductivity: Horizontal conductivities were set for each unique soil zone.
These conductivities are set to two times the saturated Green-Ampt vertical conductivities, which
have a FOS equal to 2. An excerpt of the conductivity lookup table is shown below.

27.1.2 Model Setup

27.1.2.1 1D Nodal Network
The 1D nodal network is shown to the right.
Nodes A, B and E are the ponds and nodes C
and D are manholes. All 5 of these nodes are
set to the stage/area node type.

Data forms (click “Hydrology > Mapped

Basins”) must be filled out for each mapped
basin. The node that they drain to, the time
of concentration, the unit hydrograph and
the peaking factor must be set. A sub-basin
table like with manual basins is not needed
for mapped basins. The intersections of
basins, land use and soils are done
automatically when the computational
meshes are constructed. Basin “Offsite”
shown below is included even though it does
not drain into the Regency Oaks stormwater system. It is included for groundwater recharge
purposes only. Stormwater runoff is assigned to “fictitious” time/stage node.

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Stage/area tables for nodes A, B and E were developed using the “Generate Stage/Area Table” tool
associated with pond control volumes. A 0.25-ft vertical spacing was used. An excerpt for Node A is
shown is shown below as an example.

27.1.2.2 2D Overland Flow Region

As previously mentioned, an overland flow region is required to transfer water between the surface
system and the groundwater system. In this example, the overland flow region is coincident with the
groundwater region. A combination of mapped basins and pond control volumes are used. Mapped
basins allow groundwater recharge to occur for pervious areas. Groundwater recharge is also
permitted inside pond control volumes, but when the water table pierces the ground surface inside a
pond control volume, a known head condition is applied to the respective groundwater nodes based
on the water surface in the pond.

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A pattern of breakpoints was added to each pond control volume as shown below. A uniform spacing
of 25 feet was applied.

27.1.2.3 Groundwater Region

As stated above, the overland flow region boundary is coincident with the groundwater region
boundary.

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Breakpoints were copied from the overland flow region into the groundwater region for the pond
areas (25-foot spacing). A 25-foot pattern of breakpoints was also placed along the western side of
the region for refinement purposes between ponds A and E and the region boundary. Additional
breakpoints were added at a uniform spacing of 50 feet.

Boundary stage line features were added to the groundwater model along the western side. This is
where seepage outcrops are expected along a wetland slough. Groundwater stages are forced along
these lines based on boundary stage tables. An example is shown below.

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27.1.3 Mesh Construction

The region managers link map layers and surfaces to
the mesh construction. There are separate region
managers for overland flow and groundwater.

The overland flow region manager for this example is

shown to the right. Right click on the noted fields to
select from a list of surfaces and map layers. A single
zone designated as “1” is used for the roughness and
rainfall zones. These are not used at runtime, but the
field must be filled out for mesh construction to
proceed.

The groundwater region manager settings are shown

below.

To construct and parameterize the computational

meshes, open the Scenario Manager and click the
“Build” button in the bottom left corner.

You will need to do this to run the simulations and

view the results.

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A partial display of the groundwater honeycomb is shown below. Notice the refinement of the mesh
inside the pond control volumes.

27.1.4 Simulations and Results

A single storm event consisting of 12 inches of rainfall in a 24-hour period based on the SCS Type II
(Florida Modified) rainfall distribution was simulated.

27.1.4.1 Mass Balance

The mass balance error is negligible.

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27.1.4.2 Node Time Series and Volume Charts

Stage hydrographs for the 3 ponds are shown below (use the 1D node time series reports). Ponds
“A” and “B” fully recover shortly after the storm ends. Pond “E” has not dried out after 120 hours.

Seepage inflow and outflow rates and volumes for pond “E” are shown below. There is much more
seepage into the pond than out of it. The excess seepage flows through the outfall structure, which
continues to flow at hour 120 in the simulation. Pond “E” was excavated into the side of a hill and has
intercepted groundwater flow from east to west.

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A photograph of the pond at node E is shown below on the left. The pond is usually inundated and
has a mature stand of cypress trees in it – a wetland species. Pond A is shown below right and is
typically dry. Both photographs were taken while it was raining. Groundwater profiles through these
two systems are generated in following section.

27.1.4.3 Creating Groundwater Surfaces and Profiles

On the animation panel of the Graphic View, set the “Region Type” to “Groundwater Region” and
the “Animation View Mode” to “Elevation” as shown below. Also set the “Min Threshold” to “-9999”.

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Click the “Power” button and then “Go To Relative Time” 6 hours.

Move the cursor over the animation and right click. Set the “File Root Name” to “GW-006” and the
“DEM Cell Size” to “5” feet. Check the “Generate DEM Hdr/Flt File Pair” and click “OK”.

A message will appear when the process is complete, indicating the names and locations of the three
files that were created. Notice that these files are automatically placed in the “Surfaces” folder in the
project directory.

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Repeat the above process for 12, 18, 24, 36, 48, 72, 96 and 120 hours.

Next, open the “Surface Manager” and click the “Batch Import” button at the lower right corner of
the data form. Navigate to the following folder and select all of the files shown below. Click “Open”.
A list of filenames appears – click Import again.

The new surfaces are included in the surface manager as shown below.

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These surfaces can be viewed on the raster panel of the Graphic View as shown below. The intent of
preparing these surfaces is not to illustrate an animation, but rather to cut groundwater profiles from
the DEMs using ICPR’s “Display Profile” tool.

6 hours 12 hours 18 hours 24 hours 36 hours

48 hours 72 hours 96 hours 120 hours

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Two reference polylines have been created – toggle them on.

Click the “Display Profile” icon and then move the cursor over the northern-most reference polyline
and click. Check the following boxes (below right) and click OK.

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The groundwater profiles at different points in time should appear along with the ground profile. The
groundwater table below “B” mounds significantly and the gradient is from right to left or toward the
western region boundary and pond “E”.

Here are times 24, 48, 72, 96 and 120 hours.

And here are profiles for the other reference polyline through pond “A”.

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27.2 Example 2 – Infiltration Galleries

27.2.1 Background
This example is based on a grading and drainage plan prepared and provided by Jenkins Engineering,
Inc. of Destin, Florida. Our appreciation goes out to Jenkins for granting us permission to use this
project as an example. It is also presented in Section 16.6, but percolation links were used to model
groundwater flow in that example. It was noted in that example that the groundwater mounds
between adjacent infiltration galleries would overlap and that a 2D groundwater model would be a
better approach. That, in essence, is the objective of this example – to use a 2D groundwater
approach instead of using percolation links.

Open the following project and then open and maximize the Graphic View. Click the “Zoom Extents”
icon.

The focus of this example is a set of infiltration galleries (exfiltration beds) used to dispose of
stormwater runoff from a parking lot for a condominium project in Destin. The infiltration galleries
are modeled in ICPR as French drains and are interfaced with the groundwater module. A typical
section through one of the galleries is shown below and includes 6 parallel 18-inch perforated ADS-

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N12 conduits enclosed in gravel and filter fabric. Other galleries for the project include 4 and 9
conduits in parallel as well as a single perforated pipe in one area.

Surface runoff from the parking areas enters the infiltration galleries through various inlets. Water is
dispersped through a system of parallel perforated pipes. Storage is available in the pipes and in the
gravel pit surrounding the pipes. In addition to storage and conveyance, stormwater percolates in
the soil column both vertically and horizontally. The groundwater table then responds to the
percolation and recharge by mounding and then moving horizontally based on hydraulic gradients.

The area of interest and the locations of the

various infiltration galleries for this example are
shown to the right. In all, there are six distinct
galleries.

Galleries “A” and “B” are hydraulically connected

to each other but otherwise isolated from the
other galleries. There are six 18-inch perforated
pipes in parallel and the total trench width is 24
feet.

Galleries “C”, “D” and “E” are also hydraulically

connected to each other but otherwise isolated.
Galleries “C” and “D” have nine 18-inch
perforated pipes in parallel for a total width of 36
feet. Gallery “E” includes a single 18-inch
perforated pipe.

Gallery “F” is isolated hydraulically from the

remainder of the site and includes four 6-inch

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perforated pipes in parallel with a total width of 16 feet.All of the perforated pipes in the infiltration
galleries are enveloped with gravel wrapped in filter fabric. A gravel porosity of 0.4 is assumed for
all galleries.

In addition to the grading and drainage plan, Jenkins provided a “Report of Subsurface Exploration
and Geotechnical Engineering Evaluation” prepared by Nova Engineering and Environmental. The
following stormwater management system soil design parameters were included in the Nova report.

Based on the above design parameters, the following model parameters are used in this example:

 saturated vertical conductivity: 27 fpd (F.O.S. = 2)

 saturated horizontal conductivity: 40 fpd (F.O.S. = 2)
 top of confining layer: elevation -12.5 feet (estimated)
 initial (ambient) water table elevation: 7.5 feet (approximately 5 feet b.e.g. at galleries)
 native soil fillable porosity: 0.25
 gravel fillable porosity: 0.40

Although the vertical datum for the project is unknown, the example is consistent with the grading
and drainage plan.

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27.2.2 Model Setup

27.2.2.1 1D Hydraulics
The model setup for the 1D hydraulics
is relatively straight forward. It
consists of stage/area nodes, pipe
links and French drain links. Since
there is no surface outlet, there are no
time/stage nodes. Stormwater is
disposed of entirely by percolation in
the infiltration galleries. The basic
layout is shown to the right.

Pipe hydraulics and storage in the

trench is included for French drain
links regardless of whether the
groundwater module is in play or not.
However, the objective of this
example is to integrate the two. The
“Overland Flow Region” and the
“Groundwater Region” both must be
specified in the French drain data form
to accomplish this.

Although it is possible to connect

multiple French drain links together,
there are a few important rules when
integrating them with the groundwater module. The dimensions, connecting invert elevations, link
count and mesh scaling factors must all be identical when they are connected. If they are not, an
error will occur when the “Scenario > Build” is executed. They should be separated by another link
type if the consecutive French drains are not of identical sizes. For example, infiltration gallery “D”
is 36 feet wide and gallery “E” is only 4 feet wide. They have been separated by a short pipe link.

The French drain link data form for gallery “A” is shown below. As previously stated, this gallery
includes six parallel 18-inch perforated pipes and has a total width of 24 feet. Therefore, the trench
width is set to 4 feet and the link count is set to 6 for a total width of 24 feet. Also, the mesh scaling
factor is set to 6. ICPR4 automatically creates a special control volume internally for this link with a
length equal to the trench length and a width equal to the trench width times the mesh scaling factor.

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27.2.2.2 Surface Hydrology

As stated in the introduction to this example, surface runoff from the parking areas enters the
infiltration galleries (i.e. French drains) through various inlets and from there it percolates into the
surficial groundwater system through the bottoms and sides of the galleries.

It is important to treat the ground surface directly above the infiltration galleries as impervious (even
if they are pervious) and then direct the runoff into the French drains. It will percolate into the soil
column from there. This can be accomplished by modeling the surface areas as “Manual Basins”. The
raster view of the “Manual Basins” map layer is shown below.

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27.2.2.3 Processing Manual Basins

In addition to the “Manual Basins” map layer, a layer called “Impervious-Above” was created as
shown below. Think of this as the impervious/pervious polygons above ground. The three primary
polygon designations of interest are: (1) Open; (2) Impervious; and, (3) Above Trench. The “Open”
polygons are the pervious areas. The “Impervious” polygons are parking surfaces and buildings. The
“Above Trench” polygons are directly above the infiltration galleries. Even though we are assuming
that these are impervious in terms of surface runoff, they have been intentionally separated from the
parking and building areas. The reasoning for this will become clearer a little later but basically we
want to make a clear distinction between those areas directly above the French drains and those
below the drains. The areas above the drains are treated as impervious and the areas below the
drains are treated as pervious to allow percolation from them.

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Right click on Manual Basin in the data tree to process the basin polygons (i.e. intersect map layers).
Notice that the map layer “Impervious-Above” is used as both the land cover zone and soil zone map
layer. There is only one soil type for this small site, but we need to restrict the vertical conductivity
over the French drains.

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The manual basin data form opens when the processing is

completed (just a few seconds) with the resulting breakdown of sub-
polygons for each basin. Close the form and save.

27.2.2.4 The Overland Flow Region

An overland flow region is required for the French drain links to
interact with the groundwater module. However, noother graphical
elements are required. Once the region is defined, ICPR
automatically creates a control volume internally for each French
drain link with a length equal to the trench length and a width equal
to the trench width times the mesh scaling factor. Triangle edges
are forced along the centerline of the control volume. Ground
elevations for internal nodes are set to the bottom elevation of the
trench. All other nodes are taken from the designated ground
surface in the Overland Flow Region Manager.

We only need one map layer before mesh construction – the impervious polygons. A map layer called
“Impervious-Below” is an exact copy of “Impervious-Above” except the polygons around the
infiltration galleries are labeled “Below Trench”. All other polygons are labeled the same as before.

The overland flow region manager is shown below. Notice that a single ground elevation of 13 feet
is used. Although we could prepare a detailed DEM based on the grading plan, it is not needed since

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our focus is below the ground, not above it. Also, the map layer “Impervious-Below” is used for both
the Land Cover Zones and the Soil Zones. Lookup tables are used to parameterize each unique
polygon within the map layer.

27.2.2.5 The Groundwater Region

The groundwater region extends about 160 – 180 feet from
the center of the infiltration galleries on the east and west
sides as shown below. No graphical features are needed.

The groundwater region manager is shown below. Like the

overland flow region, the ground elevation is set to 13 feet.
The confining layer top is at elevation -12.5 feet (about 25 feet
below ground elevation) and the initial water table is set to
elevation 7.5 feet (about 5 feet below the ground elevation at
the infiltration galleries.

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27.2.2.6 Lookup Tables

The impervious percentage lookup table is shown below. Notice that the “Above Trench” zone is set
to 100% impervious while the “Below Trench” zone is set to 0% impervious. The “Above Trench”
zones occur in the manual basins while the “Below Trench” designation is used for the overland flow
region.

A partial excerpt of the Green-Ampt lookup table is shown below. The saturated vertical conductivity
for all soil zones is 27 fpd except for “Above Trench” which is 0.00001 fpd – a very small value designed
to restrict infiltration above the French drains. Also notice that the difference between “MC
Saturated” and “MC Initial” is 0.25, which is the fillable porosity cited by the project’s geotechnical
engineer.

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The fillable porosity and saturated horizontal conductivity tables are shown below. The fillable
porosity for the groundwater model is 0.25 and the conductivity is 40 fpd.

27.2.3 Computational Meshes

Before executing the simulation in this example, the computational meshes must be constructed via
the “Scenario > Build”. The final overland flow (left) and groundwater (right) honeycomb meshes are
shown below. The infiltration gallery footprints are included for reference purposes. Keep in mind
that runoff from the manual basins is directed to the French drains no rainfall is applied to the
overland flow honeycomb.

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27.2.4 Simulation Control

Simulation control parameters are set in the simulation manager. The simulation duration is 72
hours. Global rainfall (a single storm distribution and storm event) is applied to the manual basins,
but no rainfall is applied to the overland flow region. In other words, all rainfall-runoff processes
occur through the manual basins.

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27.2.5 Analysis
27.2.5.1 Mass Balance
Click “Reports > Mass Balance Routing” after the simulation has completed. The percent error drops
to -1.6% at about hour 3.5 in the simulation. This occurs as the soil column below the French drains
becomes saturated and is likely due to abrupt changes in porosity and the different time increments
between surface and groundwater computations. Regardless, the maximum error is within
acceptable ranges and quickly reduces to a fraction of a percent by about hour 10.

The following chart shows the change in storage based on flows and by the change in geometry.
They are very close to one another and support the small mass balance error. Note that the
maximum overall change in storage is about 18,000 cubic feet. The exact amount of storage in all of
the French drains combined is 18,372 cubic feet. Therefore, ICPR4 is accurately accounting for the
storage in the infiltration galleries.

The cumulative volume of basin inflow (surface runoff) and seepage outflow (percolation) is shown
below. The system has almost fully recovered by hour 72 which is 48 hours after the rain has
subsided.

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27.2.5.2 Node Time Series

The various node names and locations are shown to
the right for reference purposes.

Click “Reports > 1D Node > Time Series”. Several

representative stage hydrographs are presented
below. Water levels have receded below the pipe
inverts for these nodes but is still inside the gravel bed
below the perforated pipes for all the galleries except
gallery F (node 13A). The bottom of the gravel beds for
all modeled French drains is elevation 8.5 feet.

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27.2.5.3 Animations
An animation sequence of the change in
groundwater elevation is shown on the
following page. The water table begins
mounding at the French drains as expected
and then pushes outward with time. The
mound between the two main infiltration
galleries is higher at hour 72 than directly
below the galleries.

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27.3 Example – Injection Well

This example is almost identical to the example presented in Section 15.3. It is a roadway drainage
system that includes a stormwater pump station and an injection well. A rating curve was used for
the injection well in the previous version without consideration for groundwater mounding impacts.
In this example, groundwater impacts are considered. The 1D nodal network is identical to the
previous version, except the rating curve is attached to a groundwater injection well instead of to a
time/stage node.

A groundwater region must be created, an injection well graphical feature placed in the region and a
boundary stage line must be applied to a portion of the region boundary.

Open the project shown to the right and then open

the Graphic View, maximize it and click the zoom
extents icon.

27.3.1 Groundwater Region

The groundwater region is generally circular in
shape, located about 250 feet from the injection well.
The exception is in the northeast quadrant where a
canal is located and controlled at elevation 2.0 feet.
A boundary stage line is placed along this portion of
the region boundary and groundwater stages are
force to be elevation 2.0 feet for the entire
simulation.

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27.3.2 Injection Well and Breaklines

The injection well is a groundwater point feature and is placed as shown below. Three circular
breaklines were created around the injection well (using the “O – geometric shape” option) to refine
the computational mesh.

Open the Injection Well data form.

The well diameter, mesh scaling factor and shut off elevation must be set for injection wells. The
mesh scaling factor affects the mesh resolution around the well. Two internal breaklines are created
during the “Scenario > Build”. Both are circular in shape. The first is placed at a radius equal to the
mesh scaling factor times the well diameter (2 x 2 = 4 feet in this case). The second is located twice

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this distance from the first breakline (i.e. 12 feet from the center of the well). Breaklines and
breakpoints can be added for further refinements.

The resulting computational mesh around the injection well is shown below.

27.3.3 Boundary Stage Line

The complete computational mesh is shown below along with the location of the boundary stage line
feature. As already mentioned, groundwater elevations are forced to elevation 2.0 feet along the
boundary stage line because a canal is physically located there and water levels in the canal are
controlled at elevation 2.0 feet.

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Open the boundary stage line data form. The

“Boundary Stage 1” and “Boundary Stage 2”
data fields refer to a boundary stage table. In
this case, the boundary stage table is called
“BDZ” and the stage is forced to elevation 2.0.

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27.3.4 Groundwater Properties

The two groundwater properties of concern for this example are fillable porosity and saturated
horizontal conductivity. The fillable porosity is set to 0.20 and the conductivity is set to 400 fpd.
Although 400 fpd might seem unusually high, but this project is located in Miami-Dade County and
very porous and highly permeable limestone is found only a few feet below the surface.

27.3.5 Groundwater Region Manager

The ground elevation is set to 12
feet, the initial water table
elevation at 2.0 feet, and the top
of the confining layer at -110 feet
(about 122 feet below the
surface). Injection wells cannot
discharge into fresh water in
South Florida. Consequently,
they must be deep enough to
discharge to brackish water. Also
note that the honeycomb cell size
is 0.25 feet because the mesh is
so refined around the well.

Close the region manager and

perform a “Scenario > Build” to
construct the computational
meshes. Then execute the simulation.

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27.3.6 Analysis
27.3.6.1 Mass Balance Check

27.3.6.2 Link Time Series

The relationships between pump discharge, discharge to the well and discharge over the weir to the
canal are shown below for this example (groundwater in play). Results from Section 15.3 (no
groundwater) follow. Notice the oscillations in the well discharge hydrograph when groundwater is
in play, especially between hours 2 and 6. In comparison, there are no oscillations between hours 2
and 6 when groundwater mounding is not considered. As water enters the well, the groundwater
mound builds and creates a tailwater effect on the rating curve link (recall that the well rating curves
are head dependent). Consequently, the discharge is less efficient. Stage are higher and more water
flows to the canal.

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27.3.6.3 Node Time Series

Stage hydrographs on the suction and discharge sides of the pump station are shown below for this
example (groundwater in play). Results from Section 15.3 (no groundwater) follow.

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27.3.6.4 Animations

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27.4 French Drain and Injection Well Strategies

This section describes the various options available to you when modeling French Drains and
Injection Wells along with advantages and disadvantages of each approach. There was a major
release on April 7, 2017 (v4.03.00) and an update on May 19, 2017 (v4.03.01) with some important
changes to groundwater drains. Specifically, head dependent conductance parameters can now be
used with GW drain points, lines and areas. These can be particularly useful for modeling percolation
from French drains and for drain wells.

27.4.1 French Drains

French drains are a specific 1D link type in ICPR and include a perforated pipe in a trench that is
backfilled with coarse gravel. This link type always includes the pipe hydraulics and storage in the
gravel-pipe combination.

A French drain link, like all other links in ICPR, connects two 1D nodes together, usually stage-area
node types. They can also be used to connect 1D node interface points, which are 2D overland flow
graphic elements. Percolation from a French drain link can be incorporated several ways including:
(1) adding rating curve links at the connecting nodes; (2) adding percolation links at the connecting
nodes; (3) letting ICPR automatically build OF and GW computational meshes based on the French
drain link parameters; and, (4) using a GW “drain line” feature in combination with the French drain
link.

Before discussing each of the above four approaches, it would be useful to understand a little bit
about the unique hydrogeology in southeast Florida since this is where French Drains and Injections
Wells are primarily used. There is a thin layer (e.g. less than 10 feet) of overburden on top of a
relatively thick limestone layer (e.g. more than 100 feet). The saturated horizontal conductivity is
often an order of magnitude less in the overburden than it is in the limestone. Exfiltration trenches
typically penetrate through the overburden into the highly permeable limestone. The ambient water
table is close to the surface and usually well above the bottom of the trenches and in the overburden
layer.

27.4.1.1 Rating Curve Links for French Drain Percolation

There is a publication entitled “Florida Department of Transportation District 6 ICPR Applications
Manual” dated January 2008 and prepared by ADA Engineering in Miami. This manual was prepared
a few months before the PercPack option was added to ICPR3, so percolation links were not available
at the time. Section 3.3 of the above referenced manual includes a methodology for modeling
percolation from exfiltration trenches using rating curves. I won’t go into all the details here, but
basically a family of rating curves is used that relates headwater, tailwater and discharge. The
tailwater elevations are an attempt to account for a rising groundwater elevation during the
simulation based on mounding. The rising tailwater condition has no physical basis and is only an
estimate included at a time-stage node.

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The same rating curve approach used in ICPR3 can be

used in ICPR4. A separate rating curve link is needed at
each connecting node of the French drain link. Storage in
the French drain should not be included in the
corresponding node’s stage-area table. The “Overland
Flow Region” and the “Groundwater Region” data fields
must be left blank with this approach.

You will need release v4.03.01 (or later) for this

approach.

27.4.1.1.1 Advantages
One advantage of the rating curve approach is that vertically variable saturated horizontal
conductivities can be included in the rating curve operating table. It is also a relatively simple
approach that engineers practicing in southeast Florida are familiar with, so the learning curve would
be minimal.

27.4.1.1.2 Disadvantages
There are several disadvantages with this approach, the most significant being that the water moving
through the rating curve link is lost from the system. It is my understanding that the 2D groundwater
module of ICPR is to be used. Since the “to node” for the rating curve link must be a time-stage node
with this approach, there is no mechanism to incorporate the rating curve link discharge into the
groundwater module. Also, the time-stage relationship at the “to node” is supposed to reflect
groundwater mounding, but it is only an estimate and has no physical basis.

27.4.1.2 Percolation Links for French Drain Percolation

Percolation links were added to ICPR4 with release v4.03.00. These are almost identical to those
included with ICPR3’s PercPack. It is possible to use percolation links in conjunction with French drain
links as described in Section 16.6 of the most recent ICPR4 user’s manual (April 2017). These are like
rating curve links in the sense that water stored in the French drain leaves via the percolation link and
is delivered to a time-stage node. However, groundwater mounding is incorporated in the
percolation link and is physically based. There is no need to guess how the groundwater mound rises
and falls.

Like rating curve links, the “Overland Flow Region” and “Groundwater Region” data fields in the
French drain link must be left blank. Also, release v4.03.01or later is needed for this approach.

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27.4.1.2.1 Advantages
As mentioned above, groundwater mounding impacts are automatically incorporated into
percolation links. These impacts are time dependent and physically based.

27.4.1.2.2 Disadvantages
Like the rating curve link approach, water moving through a percolation link cannot be delivered
(easily) to the 2D regional groundwater module in ICPR. Also, saturated horizontal conductivities
must be vertically averaged and cannot vary with depth in the trench. This is not considered a major
disadvantage considering the regional nature of the overall CFL SWMP model.

27.4.1.3 Automatic OF and GW Mesh Generation and Integration for French Drains
Assuming there are overlapping overland flow and groundwater regions encompassing one or more
French drain links, ICPR will automatically generate computational meshes and integrate them. The
only special requirements are that the “Overland Flow Region” and “Groundwater Region”
parameters be properly set in the French drain link data form and that an appropriate mesh scaling
factor be set. An example is provided in Section 27.2 of the most recent ICPR user’s manual.

27.4.1.3.1 Advantages
The greatest advantage of this approach is that surface water and groundwater integration with the
French drain is automatic and there is no need to incorporate other link types like ratings curves or
percolation links.

27.4.1.3.2 Disadvantages
Although the setup is relatively easy using this approach, the resulting computational meshes are
complex and very detailed. Depending on the number of French drains in the overall model, run times
can increase significantly. Also, the saturated horizontal conductivities in and near the French drains
are automatically derived from the conductivity map layer and corresponding lookup table. In other
words, the conductivities used for the groundwater model in French drain areas will also be used for
the French drain computations. There is no way to use separate conductivities in the overburden and
limestone layers. The very high conductivities in the limestone layer will likely create stability
problems in the French drains. Although the approach described in this section can be very effective
for smaller site plans, it might not be practical for large scale models like the CFL SWMP.

27.4.1.4 Using a Groundwater Drain Line in Conjunction with a French Drain

A groundwater drain line is a polyline graphic element. The elevation or depth below ground
elevation can be set at each end of the drain line. A conductance value in units of cfs per lineal foot
of drain per foot of head must be set for each drain line. This is translated into cfs per foot of head at
each groundwater node along the drain line. Lastly, the drain line must be attached to a surface node.
The head is calculated as the difference between the current elevation at a given groundwater node
along the drain line and the current elevation at the surface node. Water can flow in both directions
depending on the head differential.

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Groundwater drain lines can be implemented with French drain links as follows. The French drain link
is established as normal, except the “Overland Flow Region” and the “Groundwater Region” data
fields are left blank (like the rating curve and percolation link options described in Sections 27.4.1.1
and 27.4.1.2). Then a groundwater drain line graphic element is created and drawn directly on top of
the French drain link. The data form for the drain line must be opened and completed after it is
drawn, like that shown below. The bottom elevation of the GW drain line coincides with the bottom
of the French drain trench (elevation -10 feet in this example). The conductance is 0.009 cfs per lineal
foot of drain per foot of head. This can be easily derived from field measured permeability tests which
are usually expressed in units of cfs per square foot of side area per foot of head. It is just a matter of
multiplying this value by the number of square feet along the sides of the trench and then dividing
by the length of the drain line. Release v4.03.01 is needed for this approach.

27.4.1.4.1 Advantages
The advantages of this method are that it is easy to implement, is head dependent, allows for
different conductivities between the French drain and the underlying 2D groundwater model, and it
is more stable than the detailed mesh generation approach described in Section 2.3. Water entering
the French drain is not lost like with the rating curve link and percolation link approaches. Water
entering the French drain is delivered to the 2D groundwater module. This approach also offers a
means to generalize for regional models making it a more efficient approach for both existing
conditions and for proposed alternatives.

27.4.1.4.2 Disadvantages
The primary disadvantage is that variable vertical conductivities in the overburden layer cannot be
accommodated and an average value must be used. However, it is not likely that detailed field data
to that level will be available for a regional model.

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27.4.2 Drain Wells

There are two approaches that can be used with drain wells: (1) the groundwater injection well
element; and, (2) the groundwater drain point element. Both methods are head dependent and
directly coupled with the 2D groundwater module. Water volumes are not lost from the overall mass
balance with either of these two methods.

27.4.2.1 Groundwater Injection Well Approach

There is an example of a groundwater injection well in Section 27.3. Injection wells are 2D
groundwater graphic elements. Stage-area nodes or 1D node interface points can be connected to
an injection well with either a rating curve link or a weir link. A data form must be completed for the
injection well feature as shown below. The mesh scaling factor affects the level of mesh refinement
around the well.

27.4.2.1.1 Advantages
Injection wells are relatively easy to set up, although a little bit of extra effort is needed to set up the
1D surface components. If a weir link is connected to the injection well or if a head-discharge rating
curve link is connected to it, then it becomes a head-dependent system. Furthermore, adjustments
can be made to the rating curve to account for additional head losses caused by water density
differences due to high salinities in the groundwater system.

27.4.2.1.2 Disadvantages
The primary disadvantage of this approach is the GW computational mesh around the well is highly
detailed and refined. It can greatly increase the complexity of the overall groundwater mesh,
especially if a lot of wells are to be incorporated into the model, potentially increasing run times
significantly.

27.4.2.2 Groundwater Drain Point Approach

This approach is like the GW drain line approach used with French drains, except a drain point is used
instead of a drain line. The drain point is placed at the well location and it is referenced to a 1D surface
node which would represent the inlet structure at the top of the well. Instead of connecting the

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surface node with a weir or rating curve link, a conductance value is specified as shown below in units
of cfs per foot of head. For example, if a pump test indicates that a drain well can dispose of 600 gpm
per foot of head, the conductance would be set to 1.3368 cfs per foot of head (600 / 448.83). 1D links
are not attached to the drain point.

27.4.2.2.1 Advantages
This approach is very easy to set up and does not automatically result in a highly refined
computational mesh. It would be an efficient way to set up numerous wells in a regional model.

27.4.2.2.2 Disadvantages
The additional head loss associated with salinity differences cannot be accounted for using this
approach.

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©2017, Streamline Technologies, Inc.
User’s Manual and Technical Reference
Volume 2, Chapter 28
Continuous Simulation Example – Hydroperiod Assessment

Water Table Within 6 Inches of Ground Surface

(25% Exceedance Probability, Alternative 1)

September 2017

Streamline Technologies, Inc.
1900 Town Plaza Court • Winter Springs, Florida • 32708
407-679-1696 (voice) • 407-695-0022 (fax)
28. Continuous Simulation Example – Hydroperiod Assessment

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Contents
28. Continuous Simulation Example – Hydroperiod Assessment ..................................................... 5
28.1 Background ........................................................................................................................... 5
28.2 Base Data .............................................................................................................................. 7
28.2.1 Aerial Background Image................................................................................................ 7
28.2.2 Surfaces (DEMs) ............................................................................................................. 8
28.2.3 Map Layers ..................................................................................................................... 9
28.2.4 Lookup Tables .............................................................................................................. 10
28.2.5 Project Resources ......................................................................................................... 14
28.3 Model Setup ........................................................................................................................ 16
28.3.1 1D Nodes, Links and Cross Sections ...............................................................................17
28.3.2 Overland Flow Region .................................................................................................. 20
28.3.3 Groundwater Region..................................................................................................... 23
28.4 Region Managers and Mesh Construction ........................................................................... 26
28.4.1 Overland Flow Region Manager.................................................................................... 26
28.4.2 Groundwater Region Manager ..................................................................................... 29
28.4.3 The Scenario Build ........................................................................................................ 29
28.5 Simulation Manager and Execution ..................................................................................... 30
28.6 Analyzing Results ................................................................................................................ 33
28.6.1 Mass Balance Error ....................................................................................................... 33
28.6.2 Water Budget ............................................................................................................... 34
28.6.3 Stage and Surface Area for 1D Nodes ........................................................................... 38
28.6.4 Animations ................................................................................................................... 48

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28. Continuous Simulation Example – Hydroperiod Assessment

28.1 Background
Most of the examples presented in this manual up to this point have been for single design storm
events. Continuous simulation, on the other hand, is used to model long periods of time, up to many
decades, and includes soil moisture accounting, evapotranspiration, and highly variable rainfall with
both wet and dry cycles. One of the goals of continuous simulation is to develop a long record of
stages and flows from which a statistical analysis can be performed. For example, elevations in a
wetland system can be expressed in terms of exceedance probability using stage – duration curves.
ICPR has many tools to analyze and view results for long term simulation periods. These are explored
in this chapter.

Although continuous simulation can be performed with manual basins and without consideration of
groundwater conditions, an integrated surface and groundwater model is preferred. When manual
basins are used, a constant water table elevation is assumed and the only mechanism to recover soil
storage is by evapotranspiration.

Intersecting overland flow and groundwater regions are needed to model variable water tables and
for surface water bodies to interact with groundwater bodies. Furthermore, the curve number
method should never be used for continuous simulation because it has no mechanism to recover soil
storage or to track soil moisture and evapotranspiration. Evapotranspiration is not possible with the
1D version of ICPR, you must have the full 1D/2D version.

In this example, a network of ditches is used for drainage and to control the water table for the 615-
acre agricultural tract shown below. There are 3 outlets (pump stations) at the west end modeled as
rating curve links. There are also several internal water control structures that are modeled as weir
links.

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Two restoration alternatives are also evaluated in this example. The first alternative includes
removing the pump stations to close the outlets. The objective of this alternative is to increase
average surface water and groundwater elevations as well as the overall vertical range of water level
fluctuations to sustain a viable wetland ecosystem.

The second restoration alternative includes filling the canals and re-grading the land to create deeper
pools. There are no outlets with this alternative.

Hydroperiods of the three scenarios are quantified statistically in terms of exceedance probabilities.

Open the following project and then open the Graphic View, maximize it and zoom extents.

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There are 3 scenarios for this example: (1) Existing; (2)

Restoration Alt 1; and, (3) Restoration Alt 2. The “Display”
option in the Graphic View allows you to toggle each scenario
on and off without altering the individual view settings. The 3
scenarios are discussed further in subsequent sections.

28.2 Base Data

Modeling continuous simulation is like most other ICPR
projects – it is usually better to gather, import and prepare the
base data first before setting up the model. Each of the base
data components used in this example are discussed below.

28.2.1 Aerial Background Image

There is a single aerial background image as shown below. Notice that the “Display” option
(highlighted in yellow) is unchecked. The display option is a quick way to turn the visual display of
entire scenarios on and off without losing the various individual toggle settings within the scenario.
Unchecking the display option turns the view off and allows the aerial image to be viewed by itself.

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28.2.2 Surfaces (DEMs)

There are 5 surfaces in this project as shown below in the Surface Manager. Two of the surfaces,
“existing ground” and “grading – alt2” represent the ground surface for existing conditions and the
re-graded condition for restoration alternative 2. The other 3 surfaces represent the initial
groundwater table surfaces for each of the 3 scenarios. These were developed by first guessing at an
initial groundwater elevation and then running the model for a 3-year period. A DEM was created at
the end of the 3-year period and used as the initial groundwater table. Surfaces can be viewed on the
raster panel of the Graphic View as shown below.

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28.2.3 Map Layers

There are 6 map layers for this project as shown sorted in the map layer manager below (click
“Mapping > Map Layer Manager”). Map layer “Basins” is included for illustrative purposes only –
traditional hydrology (e.g. unit hydrographs) is not used for this project. Map layer “Grading – Alt2”
is a contour map layer type. These contours were drawn in ICPR and a DEM was generated from the
contours. Notice that there are 3 land use map layers, one for existing conditions and the other two
for the restoration alternatives. The goal of the restoration alternatives is to convert the sod fields to
a viable wetland eco system. Different land cover types are expected with each alternative.

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Map layers can be viewed in both vector and raster form. The vector and raster views of the soils map
layer are shown below as an example.

28.2.4 Lookup Tables

There are 5 different types of lookup tables used for this project. Impervious percentages and the
Green-Ampt parameters affect the ability and quantity of rainfall and surface water to move

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vertically through the soil column. Fillable porosity and saturated horizontal conductivity are
groundwater parameters and affect the horizontal movement of water in the saturated zone. The
crop coefficients are used to account for evapotranspiration from the soil column. Each of these
tables is discussed in the following sections.

28.2.4.1 Impervious Percentages

Click “Tables > Impervious Sets” to open the impervious percentages table. There are 7 unique land
cover zones (click the “Impervious” tab at the bottom left corner of the form) as shown in the table
below. All are assumed to be 100% pervious. The initial abstraction for pervious areas is set to 0.05
inches for all land cover zones except “5129: Channelized Waterway”, which is set to 0.01 inches. The
time to recover the initial abstraction is set to 24 hours in the simulation control data (discussed
later). The initial abstraction is as an interception loss or the amount of water temporarily stored on
vegetation such as leaves and branches. This water is gradually removed based on the initial
abstraction recovery time and can be thought of as additional ET.

28.2.4.2 Green-Ampt Parameters

Click “Tables > Rainfall Excess Methods > Green-Ampt Sets” to open the Green-Ampt table. There is
a single GA set called “1”. Notice that the “Refined” method is not used. This is the typical setting for
high water table conditions.

The Green-Ampt parameters (click the “Green-Ampt” tab at the bottom left corner of the form)
affect infiltration into the soil column and percolation through the unsaturated vadose zone.
Development of the various soil parameters were derived mostly from the NRCS SSURGO database
for each soil type and equations provided in Section 7.4 of this manual.

 Saturated vertical conductivities were taken directly from the SSURGO data, but were
reduced by 50% to introduce a factor of safety of 2.

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 The saturated moisture content was derived from the bulk density published in the SSURGO
data.
 Field capacity and wilting point were taken directly from SSURGO data.
 The initial moisture content was assumed to be equal to the field capacity.
 The residual moisture content, pore size index and bubble pressure were calculated from
regression equations presented in Section 7.4 with percent clay, percent sand and
saturated moisture content as independent variables.
 Percent clay and sand are available in the SSURGO data.

There are three possible settings for the “Allow

Recharge” parameter: (1) No; (2) Yes; and, (3)
Groundwater Only. The “No” selection will not allow the
soil column to drain vertically. The only way to recover
soil storage with the “No” option is through
evapotranspiration. The “Yes” selection allows vertical
drainage regardless of whether the 2D groundwater
model is in play for a given soil zone. And, the
“Groundwater Only” option will allow vertical drainage
only in areas where the 2D groundwater model is in play
for the given soil zone. The “Groundwater Only” option is used in this example.

Although the initial water table depth is arbitrarily set to 999 feet, it is inconsequential in this example
because the water table is automatically derived from the groundwater model throughout the
simulation period.

28.2.4.3 Fillable Porosity

Click “Tables > 2D Groundwater > Fillable Porosity Sets” to open the fillable porosity table. The
fillable porosity below ground is set as the Green-Ampt saturated moisture content (MC Saturated)
minus the Green-Ampt moisture content at field capacity (MC Field). The fillable porosity above
ground is set to 1. Fillable porosity is a groundwater parameter.

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28.2.4.4 Saturated Horizontal Conductivity

Click “Tables > 2D Groundwater > Conductivity Sets” to open the conductivity table. The saturated
horizontal conductivity is set to twice the saturated vertical conductivity (Kv Saturated) in the Green-
Ampt table. Saturated horizontal conductivity is a groundwater parameter.

28.2.4.5 Crop Coefficients

Details of the crop coefficient lookup table are provided in Section 7.8 of this manual. Crop
coefficient tables are required for continuous simulation modeling. ICPR uses a concept called
“reference ET” for evapotranspiration. Reference ET is calculated either inside ICPR from
meteorological data or it is loaded directly from data files. Typically, reference ET is based on a turf
grass in good condition. The reference ET rate is then adjusted by a “crop coefficient” factor.

Crop coefficient tables must be provided for each zone in the “Land Use” map layer. The crop
coefficient lookup table can be viewed by clicking “Tables > Evapotranspiration > Crop Coefficient
Sets”. As noted in the comment field of the set tab, crop coefficients are based on information
included in the “Myakka River Watershed Initiative Water Budget Model Development and
Calibration – Final Report” prepared by Interflow Engineering (December 5, 2008) and the Institute
of Food and Agricultural Sciences (IFAS) at the University of Florida.

Click the “Crop Coefficient” tab to view details for each crop coefficient zone. Note that the crop
coefficient and root depth vary with time. Irrigation sources and irrigation rules are also defined in
the crop coefficient lookup table, but are not used in this example because irrigation in this type of
farming operation is typically through water table control as opposed to applied irrigation. The
“Allow Saturated ET” option is selected for all crop types.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-13

28.2.5 Project Resources

There is a map layer called “NEXRAD” that includes 4 NEXRAD polygons, each labeled with a unique
identifier (i.e. pixel ID). Hourly NEXRAD rainfall data was obtained from the South Florida Water
Management District for each of the 4 cells dating back to January 1, 1996. Also, the USGS maintains
daily evapotranspiration data for the same NEXRAD cells, and roughly for the same period of record.
Rainfall and reference ET data files are included in the following resource folders for this project.

Here is the path to the NEXRAD data files.

Here is an excerpt for one of the NEXRAD data files.

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Here is the path to the USGS reference ET data files.

Here is an excerpt for one of the USGS_ET data files.

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28.3 Model Setup

Before discussing specifics of the model setup, it is important to understand the modeling objectives.
The intent of this modeling effort is to determine hydroperiods based on long term continuous
simulations. A hydroperiod is the time that soils, wetlands, water bodies and sites remain wet.
Therefore, the model must integrate surface hydrology and hydraulics with the surficial groundwater
system and it must do that in an efficient manner because of the extensive computational effort
required for continuous simulation models.

“Everything should be made as simple as possible – but no simpler.”

Albert Einstein

With Albert Einstein in mind, here is a list of key considerations when setting up an ICPR model for
this project:

 The weir is the most important component of a drop structure relative to continuous
simulation and weir links are generally the most efficient link type in ICPR. Therefore,
all drop structure links are modeled as weir links – the pipe component of the drop
structure is ignored.
 An overland flow region is required to integrate surface water with groundwater.
 2D overland flow is computationally intensive and should be avoided when possible
with continuous simulation. An alternative strategy using pond control volumes is
applied in this example. It captures the storage accurately but ignores friction and
travel times across the various farm fields, which is inconsequential over the long
periods of time being modeled.
 When the groundwater table pierces the ground surface, the water surface
elevations in the surface model should be used as known head conditions in the
groundwater model. This is accomplished using pond control volumes instead of
mapped basins.
 The groundwater computational mesh includes mid-nodes along the sides of
triangles as well as at the vertices. Therefore, the groundwater mesh can be coarser
than the surface mesh.

There are three (3) primary model setup tasks required for this example:

1. Setup the 1D hydraulics (nodes and links)

2. Setup the overland flow region including graphical elements
3. Setup the groundwater region including graphical elements

Instead of using traditional drainage basins in this example, the existing condition project area is
discretized into 13 level pool ponds (i.e. pond control volumes). To accomplish this, an overland flow
region is created and a special graphical element called a “pond control volume” is associated with
each of the 1D stage-area nodes. Pond control volumes are polygons. The ponds are further
discretized into a computational mesh (“the honeycomb”) that communicates directly with the

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groundwater model. Each honeycomb behaves like a traditional basin except rainfall excess is
delivered directly to its corresponding node without applying a unit hydrograph. Stage-area tables
are generated for each of them from the ground surface DEM.

The ponds are connected using weir links. Some of the weir links represent the weir components of
the drop structures and others use irregular cross sections extracted from the surface DEM.

Rating curve links are used to model the 3 pump stations at the outlet locations. Each pump station
has a 5 cfs capacity. The “on” elevation is 20 feet and the “off” elevation is 19.5 feet. The pumps are
used only in the existing condition scenario. They are turned off for restoration alternative 1 and are
completely removed from restoration alternative 2.

28.3.1 1D Nodes, Links and Cross Sections

Before proceeding, click “Mapping > Background Image Manager” and set the opacity to 50%. This
will fade the aerial image and allow better visualization of the various graphic elements. If you already
have the background image toggled on, you might have to turn it off and then turn it back on again
to see the change.

Turn on the raster view for the “Basins” map layer.

Make sure the following options are set (include check marks in the various boxes).

ICPR4 User’s Manual and Technical Reference, Volume 2 28-17

Move the cursor into the graphic work area and click once, then press “Ctrl S” to view the drainage
network in the schematic mode. You should see a schematic of the 1D model setup although your
color scheme might be different.

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This model consists of 16 1D nodes. Three (3) of them are time/stage nodes located along the western
edge of the study area and are designated “TW1”, “TW2” and “TW3”. All remaining nodes are
stage/area node types. Seven (7) of these are located inside the various canals, five (5) are in the
fields and one (1) is a marsh system near the southeast corner of the study area. Notice that a
stage/area node is placed in each of the basin polygons even though traditional basins are not used
in this example.

There are 14 weir links in total with 6 of them representing control structures and 8 that use irregular
cross sections extracted from the surface DEM. An example of an irregular cross section is shown
below. Cross section “X-FNE” is a graphic element (a weir type of cross section) that was manually
drawn in ICPR. The cross section was extracted from the ground surface DEM using ICPR’s cross
section extraction tool. It was then assigned to weir link “FNE-C4”.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-19

There are also 3 rating curve links used for the pump stations at the outlets along the western side of
the project. An example is shown below. A stage-discharge rating curve operating table called “Pump
– 5 cfs” is referenced in the links, with an “Elevation On” of 20.0 feet and an “Elevation Off” of 19.5
feet.

28.3.2 Overland Flow Region

As previously stated, intersecting overland flow and groundwater regions are required to model
surface water and groundwater interactions. This section describes the overland flow region and its
various components. For now, the focus is on the “Existing” scenario. The overland flow region
boundary is shown below for the “Existing” scenario and is the extent of the study area.

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There are 3 overland flow feature types (graphic elements) used for this project:

1. Pond Control Volumes

2. Breaklines
3. Breakpoints

Each of these is discussed in the following sections.

28.3.2.1 Pond Control Volumes

Pond control volumes are polygon graphic elements. Each one is related to a specific 1D stage/area
node. When the computational mesh is constructed for the overland flow region, the 2D overland
flow links are removed from the pond control volumes and the pond control volume is treated as a
level pool. There are 13 pond control volumes in this example, one for each of the 13 stage/area
nodes.

Stage/area tables can be generated by right

clicking on “Pond Control Volume” under the
feature types and then selecting “Generate
Stage/Area Table”.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-21

28.3.2.2 Breaklines
The canals and ditches are almost always inundated on this property. These become known head
locations for the groundwater model with heads forced by the surface water elevation – if the surface
model is setup properly. Triangle edges and vertices are guaranteed along breaklines. Elevations are
calculated at the vertices and these in turn are provided to the groundwater model in the form of a
known head condition. Therefore, breaklines are needed along the bottoms of the canals and major
ditches.

Notice in the sketch shown below that breaklines do not cross pond control volumes. This is
intentional and prevents the inadvertent generation of tiny triangles.

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28.3.2.3 Breakpoints
Breakpoints are used to further refine the computational mesh. A pattern of breakpoints in the form
of equilateral triangles with side lengths of 100 feet is used for this example. A buffer of 100 feet from
other graphical elements has been applied.

28.3.3 Groundwater Region

The groundwater region matches the overland flow region exactly. There are 3 groundwater feature
types (graphic elements) used for this project:

1. Breaklines
2. Breakpoints
3. Boundary Stage Line

Each of these is discussed in the following sections.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-23

28.3.3.1 Breaklines
All the breaklines used in the overland flow region were copied to the groundwater region using the
tool shown below. No other breaklines are needed for the groundwater region.

28.3.3.2 Breakpoints
A pattern of breakpoints in the form of equilateral triangles with side lengths of 200 feet is used for
this example. A buffer of 50 feet from other graphical elements has been applied. The groundwater
breakpoints are shown below in red superimposed with the overland flow breakpoints in black.

28-24 ICPR4 User’s Manual and Technical Reference, Volume 2

28.3.3.3 Boundary Stage Line

A ditch system is located around most of the perimeter of the study area and is controlled by external
sources. A record of average daily elevations is available and is used as a boundary condition for the
groundwater system.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-25

The boundary stage line data form is shown below and it references the boundary stage table called
“Perimeter Canals (S83_T)”.

28.4 Region Managers and Mesh Construction

28.4.1 Overland Flow Region Manager
Various settings, surfaces and map layers are specified in the overland flow region manager.
Separate region manager forms are needed for the 3 scenarios as shown below. The initial stage
surface and roughness, land cover and crop coefficient map layers vary for each scenario. A different
ground surface is used for “Restoration Alt2” and reflects the re-grading of the project site.

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ICPR4 User’s Manual and Technical Reference, Volume 2 28-27

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28.4.2 Groundwater Region Manager

The groundwater region manager for the “Existing” scenario is shown below. Although not shown,
the restoration scenarios are identical except for the initial water table surface varies for each and
restoration alt2 uses a different ground surface to reflect the re-grading of the site.

28.4.3 The Scenario Build

The last step before executing the model involves a “scenario build”
which constructs the final computational meshes and parameterizes
them. The surface honeycomb is intersected with the groundwater
honeycomb and simultaneously with the soils, land use and NEXRAD
map layers. Each sub-polygon has a set of attributes that define its
surface and groundwater nodes and its soil, land use and rainfall
properties. Rainfall, infiltration, groundwater recharge, rainfall
excess and evapotranspiration are tracked for each sub-polygon.

The overland flow and groundwater honeycombs for the “Existing”

scenario are shown below.

You must do a scenario build to execute this project and review the
results. Click “Scenario > Scenario Manager” and then click the “Build”
button in the lower left corner. Separate builds are required for each
scenario.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-29

Existing Overland Flow Honeycomb Existing Groundwater Honeycomb

28.5 Simulation Manager and Execution

Click “Simulation > Simulation Manager” to open the simulation
manager. There are 3 simulations setup for this example, one for
the “Existing” scenario and two for the “Restoration” scenarios.
The simulations begin January 1, 2002 and end January 1, 2007 –
a 5-year simulation period. The simulations can be extended
from January 1, 1996 to December 31, 2014 – a 19-year
simulation period. The 5-year simulation period used in this
example is so that they will run in a relatively short period but
provide meaningful results in the continuous simulation context. Other than the names and
scenario assignments, control settings are the same for all 3 simulations.

The calculation times are shown below. The surface hydraulics are very simple for this project with
only 16 1D nodes and 17 links for the existing scenario. Most of the computational effort is in the
hydrology because of the large number of sub-polygons and the groundwater module because of its
complexity. However, much larger time increments can be used for these two modules. A 900-
second (15 minutes) time increment is used for the hydrology. Recall that we are using hourly
NEXRAD rainfall data. The groundwater module uses an 86,400-second (1 day) time increment.

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Daily output increments (1,440 minutes) are used for all three modules – hydrology, surface
hydraulics and groundwater.

The rainfall and reference ET folders are set to “NEXRAD” and “USGS_ET” as shown below. These
were discussed in Section 28.2.5.

There are 6 lookup tables (discussed in Section 28.2.4) used for this project as noted below.

The SAOR time marching algorithm is used. There would be no advantage to use the FIREBALL
method because there are only 16 surface nodes in this model and the FIREBALL method is more
appropriate for very large complex surface models. Notice that the “Initial Abstraction Recovery
Time” is set to 24 hours. This is the amount of time required to fully recover (i.e. evaporate) any water
stored as initial abstraction.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-31

The “Existing” and “Restoration Alt1” simulations took about 30 minutes each to complete on an Intel
I7 – 4.0 GHz processor and the “Restoration Alt2” took about 8 minutes.

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28.6 Analyzing Results

28.6.1 Mass Balance Error

The mass balance error for all 3 simulations is well within acceptable levels. The worst case is at the
beginning of the “Restoration Alt2” simulation at about -1.5% but is mostly between -0.2% and 0.0%.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-33

28.6.2 Water Budget

The hydrologic water budget is analyzed first. Click “Reports > Mass Balance > Hydrology”.

The mass balance report volumes are cumulative and we only need the values at the end of the
simulation. If you set the start and end times to the corresponding simulation end time (January 1,
2007), then only the last output value will appear in the report.

Make sure the “Report” tab is selected and then make the following settings and then click the “View
Report” button.

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Cumulative volumes, in inches, appear for the entire simulation for each of the 3 scenarios.

“Rainfall Excess” in the table above is the surface runoff delivered to the surface hydraulic network.
This is the precipitation amount minus ET, initial abstraction and infiltration. The infiltration amount
is equal to the recharge volume (delivered to the groundwater model) plus the stored volume (change
in soil storage). A negative rainfall excess volume can occur when there is ponded water with no
rainfall – ponded water can seep into the soil column or evaporate.

A summary of the hydrologic water balance for the 3 simulations, annualized over the 5-year period,
is presented below. Notice that the ET increases and infiltration decreases for the restoration
alternatives. This is due in part to change in vegetation, but it is also because the surface outlets were
eliminated with the restoration alternatives and more water was available for evapotranspiration.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-35

Component Existing Restoration Alt1 Restoration Alt2

Gains
Precipitation 48.53 48.53 48.53

Losses
Initial Abstraction 3.29 3.29 3.38
ET Actual 34.45 38.32 42.55
Infiltration 10.20 7.28 3.26
Total Losses 47.94 48.89 49.19

Surface Runoff 0.59 -0.36 -0.66

Annualized Hydrologic Water Budget Summary (all units in inches per year)

Next, let’s look at the surface water budget. The “1D Nodes > Aggregate” report is used. This report
adds volumes from multiple nodes.

Set the start and end times to January 1, 2007 again to match the simulation end time.

Select only the interior nodes (i.e. the stage – area nodes, not the time – stage nodes). You will have
to do this for each scenario.

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Make the following settings and then click the “View Report” button.

The volumes are in acre-feet and are cumulative values for the entire simulation. Notice that there
are “Inflow” and “Outflow” volumes for each category. To obtain the net volume, you must subtract
the outflow volume from the inflow volume. Sometimes the net volumes will be negative meaning
there is more outflow than inflow. The “Basin” category is the rainfall excess volume or surface runoff
volume from the hydrology component of the model. Basin inflows occur when the precipitation
exceeds the sum of ET, initial abstraction and infiltration. Basin outflows occur when the sum of ET,
initial abstraction and infiltration exceed the precipitation.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-37

Link inflows and link outflows are the sum of all links in the model. Link inflow and outflow equal each
other for the restoration projects because the outlets were eliminated.

Seepage includes groundwater flows from the perimeter ditch as well as interior seepage.

The surface water budget presented below is in inches per year over the project area (614.48 acres)
based on the 5-year simulation period.

Component Existing Restoration Alt1 Restoration Alt2

Gains
Surface Runoff 0.59 -0.36 -0.66
Seepage 52.71 0.30 0.65
Total Gains 53.30 -0.06 -0.01

Losses
Surface Outlet 53.35 0.00 0.00

Surface Storage -0.05 -0.06 -0.01

Annualized Surface Water Budget Summary (all units in inches per year)

28.6.3 Stage and Surface Area for 1D Nodes

There are several ways to report on
and analyze stage and surface area for
1D nodes. The quickest and easiest
way to do this is with custom reports.
After opening the custom report
manager, follow the instructions
below.

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ICPR4 User’s Manual and Technical Reference, Volume 2 28-39

This is the stage hydrograph for node “Field SE 1” and for simulation “Existing”. The warning stage is
the elevation at which this field begins to flood. The field is below the warning stage and in the
ditches most of the time, which is the intent of ditches and pump stations.

The stage hydrograph for Restoration Alt1 is shown below. Recall that this alternative eliminates the
pump stations. Consequently, there is no surface outlet. Field SE 1 is inundated much of the time.

28-40 ICPR4 User’s Manual and Technical Reference, Volume 2

The stage hydrograph for Restoration Alt2 is shown below. This alternative includes eliminating the
surface outlet, filling the ditches and re-grading the fields. Although this field dries out from time to
time, it is inundated for longer periods of time.

This is the stage for node “Field SE 1” and for simulation “Existing” expressed in terms of exceedance
probability. The straight red line is the warning stage and in this example, it represents the low field
elevation or the elevation at which this field begins to flood. The warning stage crossing the
exceedance probability curve at about 5%, meaning that stages will be higher than elevation 23.4
feet 5% of the time (about 18 days a year) on average over a long period of time.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-41

Eliminating the pump stations (restoration alt1) causes this field to flood about 70% of the time (more
than 8 months a year). It is about 3 inches deep or greater 25% of the time (3 months a year).

Re-grading the fields, filling the ditches and eliminating the surface outlets keeps Field SE flooded
about 65% of the time (slightly less than 8 months a year). A flood depth of 6 inches or greater is
expected 25% of the time (3 months a year).

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The following is the wetted surface area in square feet of node “Field SE 1” for simulation “Existing”
expressed as an exceedance probability. The wetted surface area is approximately 84,000 square
feet (1.93 acres) at the 25% exceedance probability.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-43

The wetted surface area for restoration alt1 is about 520,000 square feet (11.94 acres) for the 25%
exceedance probability, about 6 times greater than the existing condition.

There are about 1,120,000 square feet (25.71 acres) inundated at a 25% exceedance probability for
restoration alt2. This is more than 2 times greater than alt1 and 13.3 times greater than the existing
condition. However, it is a more complicated and expensive implementation effort.

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Raster charts of depth above the warning stage are presented below for the 3 scenarios. These charts
provide a visual means to determine wet and dry periods, and how the depth of flooding is dispersed
throughout the year.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-45

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ICPR4 User’s Manual and Technical Reference, Volume 2 28-47

28.6.4 Animations
There are thousands of data points at every surface and groundwater vertex for the 5-year simulation
period executed in this example. Although ICPR has reporting tools to access results for individual
vertices, it would be tedious at best to analyze results like that. Instead, animations provide an easier
tool for visualizing results. For example, an animation of surface water elevations at each of the daily
output increments can be played. Furthermore, surface and groundwater elevations can be
expressed in terms of exceedance probabilities, which is a much easier and useful way to visualize
and review long simulation periods.

Before continuing, set the animation palette as follows.

Close the color palette selector.

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28.6.4.1 Maximum Depth

Open the animation tab on the Graphic View and set the following fields.

Click the “power” button and then click the “end” button.

The maximum flood depths for the 5-year simulation period appear. Most of the flooding is in the
channels and only minor flooding occurs in the fields.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-49

Repeat the process for “Restoration Alt1”. The maximum flood extents expand much farther into the
fields with this alternative, but the flood depths are mostly less than 1 foot except in the channels.

Repeat the process for “Restoration Alt2”. Recall that this option included filling the ditches and re-
grading the fields. There is a greater vertical fluctuation in flood depths with this alternative.

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28.6.4.2 Depth % Exceedance

Set the following fields.

You might need to click the power button off and then on again. Set the “relative time” to 10, which
is the 10% exceedance probability for this animation option. Click the “Go To Relative Time” button.
Repeat for 20% and 30%.

Results are shown on the following page.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-51

The flood extents for the 10%, 20% and 30% exceedance probabilities (36.5, 73.0 and 109.5 days per
year on average, respectively) are shown below.

Restoration Alt1

10% Exceedance 20% Exceedance 30% Exceedance

Repeat the above process for “Restoration Alt2”.

10% Exceedance 20% Exceedance 30% Exceedance

28-52 ICPR4 User’s Manual and Technical Reference, Volume 2

28.6.4.3 Change in Groundwater Elevation

Set the following fields.

You might need to click the power button off and then on again. Set the “relative time” to 21,168
(June 1, 2004 – end of the dry season). Click the “Go To Relative Time” button. Repeat for hour 24,096
(October 1, 2004 – end of rainy season).

Results are shown on the following page.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-53

The warmer colors are generally drier conditions and the cooler colors are generally wetter. Try
setting the “sleep rate” to 0.05 seconds and play the animation from the beginning. Try the other 2
scenarios.

Restoration Alt2

June 1, 2004 October 1, 2004

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28.6.4.4 Groundwater Elevation Exceedance Probability

Set the following fields.

You might need to click the power button off and then on again. Set the “relative time” to 25 (the
25% exceedance probability). Click the “Go To Relative Time” button.

Right click anywhere in the viewing area to generate a DEM. These are stored in the project’s
“Surfaces” folder as *.flt, *.hdr file pairs.

Repeat this for the 50% and 75% exceedance probabilities. And then repeat the whole process for
“Restoration Alt1” and “Restoration Alt2”.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-55

Open the surface manager.

Click the “Import” button in the lower left corner.

Navigate to the following folder and select the 9 files shown below. Then click the open button. A list
of the files will appear – click the Import button again. These will appear in the surface manager when
the import is complete.

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The 9 surfaces that were just imported can be viewed from the raster tab of the graphic view just like
any other surface. However, the “display profile” tool will be used to evaluate the existing condition
and alternatives.

Toggle the reference polylines on for scenario “Restoration Alt2” as shown below. Click the “Display
Profile” tool and then click the northern-most reference polyline.

Select the surfaces shown to the right and then click

OK. Repeat for the 50% and 75% exceedance
probabilities. The 3 profiles are shown on the
following page.

ICPR4 User’s Manual and Technical Reference, Volume 2 28-57

Existing Grade – 25% Exceedance Probability for Existing and Restoration Alt1 Scenarios

Existing Grade – 50% Exceedance Probability for Existing and Restoration Alt1 Scenarios

Existing Grade – 75% Exceedance Probability for Existing and Restoration Alt1 Scenarios

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Now click the Display Profile tool again and then select the
southern-most reference polyline. Make the surface
selections shown to the right and then click OK. The
profiles are shown on the following page.

Existing and Proposed Grades – 25% Exceedance Probability for Restoration Alt2

Proposed Grade – 25%, 50% & 100% Exceedance Probabilities for Restoration Alt2

ICPR4 User’s Manual and Technical Reference, Volume 2 28-59

28.6.4.5 Groundwater Table within 6 Inches of Ground Surface

The various groundwater surfaces that were created in the previous step can be imported into GIS
for further manipulation. For example, Spatial Analyst in ArcGIS can be used to determine the
extents of the groundwater table within 6 inches of the ground surface based on a 25% exceedance
probability (3 months a year on average over a long period of time). This might support a wet prairie
community. You will need the *.hdr, *.flt file pairs that are automatically saved in the project
“surfaces” folder. Here is a comparison of the extents of the groundwater table within 6 inches of the
ground surface based on the 25% exceedance probability for existing conditions and the two
alternatives.

Existing Condition Restoration Alt1

Restoration Alt2

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