3 | Water Supply Planning and Development 1

UNIT 3: Assessment of water quantity: Surface monitoring,

Groundwater

3.0 Intended Learning Outcomes

At the end of the lesson, you should be able to evaluate water quantity.

3.1. Introduction

The understanding of comprehensive water resources planning and management is

becoming increasingly important as the demand for water increases and the reliability of
existing supplies decreases, not just in the Philippines, but all over the world. In this learning
packet, we will discuss the course CES 3: Water Supply Planning and Development (3-unit
subject) with the following topics, composed of 9 Learning Packets (LP):
LP 1. Importance of safe drinking water on public health.

LP 2. Common sources of water supply: Surface water, Groundwater, Mixed water

resources, Rainwater.

LP 3. Assessment of water quantity: Surface monitoring, Groundwater.

LP 4. Water characteristics and drinking water: Parameters and standards with

regards to physical, chemical, bacteriological and organoleptical properties; Water
related diseases; Factors affecting water quality; Sources of environmental
contaminants.

LP 5. Estimation of water demand: Classification of water use, Quantifying present

and future use, domestic water demand, Industrial, commercial, agricultural and
other types of water demands, Fluctuations in water use, factor of inequality low rate
patters.

LP 6. Development of water sources: Groundwater, Construction of wells,

Environmental effects and sea water intrusion, Surface water, Watershed and
reservoir management and dam siltation.
LP 7. Introduction to conventional water purification processes: Physical treatment
process, Chemical treatment processes.

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LP 8. Water transport and distribution systems: General procedure and layout of

masterplan of a distribution system, Design criteria for normal and fire demand,
Hydraulic design of branched and grid systems, Pipes, appurtenances and pipe
laying, metering, flow and pressure control.

LP 9. Introduction to water laws, codes, finance and water rates

This learning packet (LP) is a self-directed material, wherein you are going to learn on
your own. This learning packet has series of instruction, discussion, and assessment of
learning about the course content.
At the end of the lessons in this LP you need to complete the student’s task and submit
back to me by using the packaging material in this LP.

3.2 Assessment of water quantity

What is water quantity? What does it mean?

Water quantity means the amount of water that is present in a river, lake, wetland or
aquifer at a particular point in time. Water quantity varies naturally in water bodies due to
climate, land cover, and underlying geology. Natural variability in water flows and levels is
important for the health of aquatic ecosystems and many of the services that they provide
(for example, fisheries). However, water quantity is also influenced by human activities, such
as water takes, diversions, dams, bores and some uses of land.

Water quantity management involves defining the amount of water that is required to
remain in a water body to provide for ecosystem health and other in-stream values, and the
available water that can be used. It also involves effectively and efficiently managing
activities that affect water quantity.

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3.2.1 Surface monitoring

So, how do we measure and monitor the quantity of water, for example,
in a lake or a dam?

3.2.1.1 Water level in reservoirs (Lakes, Dams and others)

Water reservoirs vary in size and shape considerably, depending if they

are a ‘service reservoir’ for local storage of treated water, naturally occurring
‘lakes’ that are used for drinking water or ‘man-made’ reservoirs by placing a
dam across a valley. How water level in reservoirs will be measured will
therefore also depend on which type of reservoir is being monitored.

Typically, in a service reservoir, the volume of water contained in it is

well known and by level monitoring, the flow through the reservoir and the
extraction rate of water can be controlled to maintain a stable water supply. The
demand for water will cause the water level in reservoirs to fall and level
monitoring can control pumps to refill as required. Monitoring not only helps
to prevent the service reservoir from overflowing but also from running empty
and raising alarms if there is a failure in the pump control.

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3.2.1.2 Water level in reservoirs monitored by level probes

The instrument for water level monitoring, the level probe or

submersible pressure transmitter is suspended by its cable into the inspection
chamber of the service reservoir. This provides easy access for service,
calibration and replacements. If the water in the service reservoir is turbulent,
then the hydrostatic level transmitter may be installed by suspending it inside
a stilling tube within the reservoir instead.

The water level in reservoirs that are formed naturally such as lakes or
by a man-made dam across a valley will also require monitoring using a
submersible pressure transmitter. As these reservoirs can be very large and
store vast amounts of water, the highest accuracy level probes are required, as
a change of a few millimeters or 1/8” in the water level may represent many
thousands of liters or gallons of water. In these cases, the shape of the reservoir
is charted and a level probe’s stability and accuracy are critical in determining
the correct amount of water present at any given time. Sometimes the water
temperature may also be measured by the hydrostatic level transmitter, to
integrate the calculation of thermal effects caused by the temperature behavior
of water and its change of specific gravity.

Water level in reservoirs, that have been formed naturally, is often

measured by installing a monitoring system in a stilling tube located in an
instrument tower near the pump used for water extraction. This instrument
tower will be built at the lowest possible or lowest permitted level of water
extraction. In reservoirs that have a dam, the extraction points may even be a
part of the dam. If the monitoring system is then installed in the extraction
chamber, it has to be protected from the effects of water flow from the reservoir
which can cause inaccurate measurements by turbulence.

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Level monitoring of water level in reservoirs using submersible pressure

transmitters has proven over time to be the most simple, reliable and accurate
method to control the water level in reservoirs.

Image adapted from www.unidata.com.au

3.2.1.3 Water Quantity Information

• Water quantity calculation can be done through water balance modelling as

the difference between precipitation inputs and river flow, groundwater
recharge and evaporation outputs.

• River flow data are one of the most important sources of information, as
river flow represents one of the main sources of water for human and
animal consumption, irrigation and navigation, as well as a source of
hydroelectric power.

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• Information on lake, dam and reservoir levels and volume, dam and
reservoir releases and transmission losses are also important in assessing
the availability of water.

• River flow cannot easily be measured directly, but is generally computed

from records of river water level converted to flow, or discharge, using a
rating curve or table. A rating curve is a relationship between river level, or
stage, and river flow or discharge and, except where sited at specifically
designed hydraulic measuring structures, must generally be derived for
each gauging station over a number of years by measuring discharge over
a wide range of stage (river level).

• Water levels for lakes and reservoirs will normally be converted into storage
volumes using appropriate area measurements.

3.2.1.4 Water Balance Equation

A general water balance equation is:

Image adapted from https://i.ytimg.com/vi/P_3nT4BzMvw/hqdefault.jpg

This equation uses the principles of conservation of mass in a closed

system, whereby any water entering a system (via precipitation), must be

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transferred into either evaporation, surface runoff (eventually reaching the

channel and leaving in the form of river discharge), or stored in the ground.
This equation requires the system to be closed, and where it isn't (for example
when surface runoff contributes to a different basin), this must be taken into
account.
A water balance can be used to help manage water supply and predict
where there may be water shortages. It is also used in irrigation, runoff
assessment (e.g. through the RainOff model), flood control and pollution
control. Further it is used in the design of subsurface drainage systems which
may be horizontal (i.e. using pipes, tile drains or ditches) or vertical (drainage
by wells). To estimate the drainage requirement, the use of a hydrogeological
water balance and a groundwater model (e.g. SahysMod ) may be instrumental.
The water balance can be illustrated using a water balance graph (see
below) which plots levels of precipitation and evapotranspiration often on a
monthly scale.

Image adapted from https://geographyiseasy.wordpress.com

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3.2.1.5 Other Models

Runoff model (reservoir)

A runoff model is a mathematical model describing the rainfall–runoff
relations of a rainfall catchment area, drainage basin or watershed. More
precisely, it produces a surface runoff hydrograph in response to a rainfall
event, represented by and input as a hyetograph. In other words, the model
calculates the conversion of rainfall into runoff.

Image adapted from CSIRO Land and Water.

A well-known runoff model is the linear reservoir, but in practice it has

limited applicability.
The runoff model with a non-linear reservoir is more universally
applicable, but still it holds only for catchments whose surface area is limited
by the condition that the rainfall can be considered more or less uniformly
distributed over the area. The maximum size of the watershed then depends
on the rainfall characteristics of the region. When the study area is too large, it

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can be divided into sub-catchments and the various runoff hydrographs may
be combined using flood routing techniques. Rainfall-runoff models need to be
calibrated before they can be used.

Linear reservoir
The hydrology of a linear reservoir (figure 1) is governed by two
equations.

1. flow equation: Q = A·S, with units [L/T],

where L is length (e.g. mm) and T is time (e.g. h, day)
2. continuity or water balance equation: R = Q + dS/dT, with units [L/T]
where:
Q is the runoff or discharge
R is the effective rainfall or rainfall excess or recharge
A is the constant reaction factor or response factor with unit [1/T]
S is the water storage with unit [L]
dS is a differential or small increment of S
dT is a differential or small increment of T

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Runoff equation
A combination of the two previous equations results in a differential
equation, whose solution is:

Q2 = Q1 exp{−A (T2 − T1)} + R[1 − exp{−A (T2 − T1)}]

This is the runoff equation or discharge equation, where Q1 and Q2 are

the values of Q at time T1 and T2 respectively while T2−T1 is a small-time step
during which the recharge can be assumed constant.
Computing the total hydrograph

Provided the value of A is known, the total hydrograph can be obtained

using a successive number of time steps and computing, with the runoff
equation, the runoff at the end of each time step from the runoff at the end of
the previous time step.

Unit hydrograph

The discharge may also be expressed as: Q = − dS/dT . Substituting

herein the expression of Q in equation (1) gives the differential equation dS/dT
= A·S, of which the solution is: S = exp(− A·t) . Replacing herein S by Q/A
according to equation (1), it is obtained that: Q = A exp(− A·t) . This is called
the instantaneous unit hydrograph (IUH) because the Q herein equals Q2 of the
foregoing runoff equation using R = 0, and taking S as unity which makes Q1
equal to A according to equation (1).

The availability of the foregoing runoff equation eliminates the necessity

of calculating the total hydrograph by the summation of partial hydrographs
using the IUH as is done with the more complicated convolution method.

Determining the response factor A

When the response factor A can be determined from the characteristics

of the watershed (catchment area), the reservoir can be used as a deterministic
model or analytical model.

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Otherwise, the factor A can be determined from a data record of rainfall

and runoff using the method explained below under non-linear reservoir. With
this method the reservoir can be used as a black box model.

Conversions

1 mm/day corresponds to 10 m3/day per ha of the watershed

1 l/s per ha corresponds to 8.64 mm/day or 86.4 m3/day per ha

3.2.2 Groundwater monitoring

So, what is groundwater?

Groundwater is the water found underground in the cracks and spaces in soil,
sand and rock. It is stored in and moves slowly through geologic formations of soil,
sand and rocks called aquifers.

Image adapted from groundwater.org

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Aquifers are typically made up of gravel, sand, sandstone, or fractured rock,

like limestone. Water can move through these materials because they have large
connected spaces that make them permeable. The speed at which groundwater flows
depends on the size of the spaces in the soil or rock and how well the spaces are
connected.

Groundwater can be found almost everywhere. The water table may be deep
or shallow; and may rise or fall depending on many factors. Heavy rains or melting
snow may cause the water table to rise, or heavy pumping of groundwater supplies
may cause the water table to fall.

Groundwater supplies are replenished, or recharged, by rain and snow melt

that seeps down into the cracks and crevices beneath the land's surface. In some areas
of the world, people face serious water shortages because groundwater is used faster
than it is naturally replenished. In other areas groundwater is polluted by human
activities.

Water in aquifers is brought to the surface naturally through a spring or can be

discharged into lakes and streams. Groundwater can also be extracted through a well
drilled into the aquifer. A well is a pipe in the ground that fills with groundwater. This
water can be brought to the surface by a pump. Shallow wells may go dry if the water
table falls below the bottom of the well. Some wells, called artesian wells, do not need
a pump because of natural pressures that force the water up and out of the well.

In areas where material above the aquifer is permeable, pollutants can readily
sink into groundwater supplies. Groundwater can be polluted by landfills, septic
tanks, leaky underground gas tanks, and from overuse of fertilizers and pesticides. If
groundwater becomes polluted, it will no longer be safe to drink.

3.2.2.1 Groundwater level measurement

If aquifers are used for water extraction or monitored by hydrometry, a reliable

and accurate groundwater level measurement is essential. Aquifers will always
follow the contours of the permeability of the soil. They will consist of

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underground pockets held in the soil or fragmented rock and may not have a
flat level surface, due to local impermeable layers above and below the aquifer.
To establish more information and to quantify or test the water resource in the
soil, monitoring wells will be sunk in to the ground. These monitoring wells
are used for measurement of groundwater level, mineral content, location and
water quality.

3.2.2.2 Charting an aquifer

Groundwater level measurement is often logged to survey and chart an

aquifer. It is used to inspect the groundwater resource, where it is, how much
volume it contains and at what depth it is located. Separate aquifers may be
located at differing depths and thus require multiple sensors for a complete
groundwater level measurement. This groundwater level measurement may
also be recorded to determine the effect of precipitation, seasonal changes and
water extraction.

When a well or deep bore well is commissioned for extracting water, the
water company running the extraction uses the groundwater level
measurement in the extraction well and in surrounding monitoring wells to
make sure that they are not pulling the water level down too quickly and to
secure that the resource can recover from the extraction. By pumping in set
cycle times, they compare the data from the groundwater level measurement
before and after the pumping cycle at varying periods. Thereby they are able
to determine the recovery rate of the aquifer and how the underground water
resource is affected by local weather, especially how much and how fast it
reacts to certain amounts of precipitation.

Groundwater level measurement is mostly performed by a submersible

pressure transmitter. These hydrostatic level transmitters are small in diameter
and directly suspended by their cable into the well, borehole, deep bore well or
monitoring well.

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3.2.2.3 Measuring quantity

To determine and monitor the quantity of groundwater resources,

‘depth to water’ are measured in groundwater wells. This involves measuring
the distance from a reference point on the Earth’s surface to the top of the water
table beneath the surface.

Image adapted from www.slocountypwd.org/

Monitoring 'depth to water' is vital to understanding and sustainably

managing the quantity of groundwater within an aquifer. The depth changes
depending on the time of year, the amount of recent rainfall, and the amount
of groundwater being accessed by irrigators. Seasonal and long terms trends
can be identified by analyzing depth to water data. Additional interpretive
products can be created, such as hydrographs, potentiometric surface maps
and groundwater models, for technical experts.

3.2.2.4 Determining Recharge Rates

Pump test are used to determine recharge rates. First the depth of the
groundwater table is measured and then the full capacity of the pump is used

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to withdraw as much water over a fixed time period. This creates a cone effect
and once the pumping is stopped then the water table will retune to its original
level over time. Knowing the time of return to the original water level allows
the determination of flow rates to the well. This can then be used to calculate
the extent of the water capture zone over a 60 day or one-year period. The rate
of recharge depends on the hydraulic conductivity.

Image adapted from http://ubclfs-wmc.landfood.ubc.ca

3.2.2.5 Pumping Test

A pumping test is a field experiment in which a well is pumped at a

controlled rate and water-level response (drawdown) is measured in one or
more surrounding observation wells and optionally in the pumped well
(control well) itself; response data from pumping tests are used to estimate the
hydraulic properties of aquifers, evaluate well performance and identify
aquifer boundaries. Aquifer test and aquifer performance test (APT) are
alternate designations for a pumping test. In petroleum engineering, a
pumping test is referred to as a drawdown test.

The goal of a pumping test, as in any aquifer test, is to estimate hydraulic

properties of an aquifer system. For the pumped aquifer, one seeks to

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determine transmissivity, hydraulic conductivity (horizontal and vertical) and

storativity (storage coefficient). In layered systems, one also uses pumping tests
to estimate the properties of aquitards (vertical hydraulic conductivity and
specific storage). Pumping tests can identify and locate recharge and no-flow
boundaries that may limit the lateral extent of aquifers as well.

Image adapted from http://www.aqtesolv.com

Typically, aquifer properties are estimated from a constant-rate

pumping test by fitting mathematical models (type curves) to drawdown data
through a procedure known as curve matching (Figure below). Diagnostic tools
such as derivative analysis are useful for identifying flow regimes and aquifer
boundaries from a pumping test prior to performing curve matching.

Prior to performing a pumping test in the field, one should spend time
in the office developing a thorough plan for the test. Proper planning includes
the design of the test, acquisition and preparation of field equipment,
measurement and control of flow rates, measurement locations and schedules

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(with pre- and post-test collection periods) for water levels, disposal of pumped
water and test duration.

Image adapted from http://www.aqtesolv.com

3.2.2.6 Rate Measurement

Measuring the flow rate during a pumping test can be accomplished in a

number of ways including the following:

• calibrated container and stopwatch

• in-line flowmeter
• orifice weir
• weir or flume

Flow rates should be recorded with sufficient frequency to demonstrate a

constant rate or to monitor planned rate changes. In the event of temporary test
interruption (e.g., power failure), pumping stop and restart times should be
noted to allow for proper interpretation of the test. Bear in mind that the
discharge rate often decreases with time as the water level in the control well
drops.

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Volumetric Method

Flows can be determined by measuring volume. The equipment

necessary are a wrist watch or timer and a bucket or drum of known volume.
The method consists of determining the time required to fill the bucket. For
more accurate results, the measurement is repeated several times, and the
average time of these trials is taken. Note that using a bigger container will
improve the accuracy of the measurement. For example, an empty oil drum is
used as the container.

V-Notch Weir Method

A weir is an overflow structure built across an open channel for the

purpose of measuring the rate of flow of water. Weirs may be rectangular,
trapezoidal or triangular in shape. The Triangular or V-Notch Weir is a flow
measuring device particularly suited for small flows. The V-Notch Weir often
used in flow measurements is the 90° V-Notch shown in Figure below.

A 90° V-Notch Weir can be cut from a thin sheet of metal or plywood
and is placed in the middle of the channel and water is allowed to flow over
it. The water level in the channel is then measured using a gauging rod as
shown in Figure below. The zero point in the rod should be level with the
bottom of the notch. For a known height of water above the zero point in the

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rod, the flow in LPS can be obtained by using Figure below and Table A or
using the formula:

Q= 4.4 H 2.48
Where:
Q = discharge rate in liters
H = Height of Water Level on the weir in decimeters

An application of the preceding formula to determine spring yield is

demonstrated in the example below.

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3.2.2.7 Groundwater models

Groundwater models may be used to predict the effects of hydrological

changes (like groundwater abstraction or irrigation developments) on the
behavior of the aquifer and are often named groundwater simulation models.
Also, nowadays the groundwater models are used in various water
management plans for urban areas.

As the computations in mathematical groundwater models are based on

groundwater flow equations, which are differential equations that can often be
solved only by approximate methods using a numerical analysis, these models
are also called mathematical, numerical, or computational groundwater
models.

The mathematical or the numerical models are usually based on the real
physics the groundwater flow follows. These mathematical equations are
solved using numerical codes such as MODFLOW, ParFlow, HydroGeoSphere,
OpenGeoSys etc.

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Download:

Aquifer Testing
https://www.marlborough.govt.nz/repository/libraries/id:1w1mps0ir17q9sgxa
nf9/hierarchy/Documents/Environment/Groundwater/Groundwaters%20of%2
0Marlborough%20List/K%20Chapter10.pdf

Guides
Measuring water levels by use of a graduated steel tape (USGS 2010) (pdf)
https://drive.google.com/file/d/0B4k9mlxbygW2Tnk0ajVyNUFZbmc/edit

Measuring water levels by use of an electric tape (USGS 2010)(pdf)

https://drive.google.com/file/d/0B4k9mlxbygW2OFhCNzZyaVVVSUk/edit?us
p=sharing

Visit URL:
Pumping Tests
http://www.aqtesolv.com/pumping-tests/pump-tests.htm
3.3 Video Lessons

Click and watch the following videos:

Hydrogeology 101
https://www.youtube.com/watch?v=G7CnE5NBxZs

Water Balance Example 1

https://www.youtube.com/watch?v=g1OeNwq9fd8

Hydrologic Budget Example

https://www.youtube.com/watch?v=Q_Ur6F4hDVI

Water Budget Primer

https://www.youtube.com/watch?v=51fM3ginvKA

Rainfall Runoff Model

https://www.youtube.com/watch?v=g4DyyDsf6EI

Measuring Groundwater with Steel Tape

https://www.youtube.com/watch?v=b23FvXkD6VM

Water Level Sensor Types and how they work!

https://www.youtube.com/watch?v=bHxEXlIHSHY

Unconfined Aquifers vs. Confined Aquifers

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https://www.youtube.com/watch?v=wx0w-Az5JOY

Automatic Reservoir Monitoring And Control

https://www.youtube.com/watch?v=6wxDApKXGTg

Student’s Task 03

Please answer the following:

1. What is a water level sensor? How does it work?
2. What is the Water Balance Equation? Explain
3. What is an aquifer?
4. What is ground water recharge rate? How would you measure it?

Write your answers in a bond paper and submit. If you have internet, submit a soft
copy online.

3.4 References

RURAL WATER SUPPLY Volume 1: DESIGN MANUAL. 2012. Water Partnership

Program (WPP). The World Bank Office Manila
TECHNICAL MATERIAL FOR WATER RESOURCES ASSESSMENT.
TECHNICAL REPORT SERIES No. 2 World Meteorological Organization, 2012.
Water level in reservoirs. 2020/8/03. Retrieved from
https://en.wika.com/newscontentgeneric_ms.WIKA?AxID=462
What is Groundwater? 2020/8/03. Retrieved from
https://www.groundwater.org/get-informed/basics/groundwater.html
Water balance, water cycle. 2020/8/03. Retrieved from
https://naturalsciences.ch/topics/water/water_balance

3.5 Acknowledgment

The images, tables, figures and information contained in this module were
taken from the references cited above.

C. M. D. Hamo-ay