SWAT Hydrological
ModelAdapted for Water
Resources Management
Sandhya Rao
INRM Consultants, New Delhi
History
SWRRB - Early 80's -Modified CREAMS
SWAT - Early 90's -Modified
SWRRB Reach Routing
Structure
Watershed
TAES-IITFlexible
Delhi MoA
- 1996, to collaborate
Configurations
in further
development of the model
Model Attributes
a model which can handle river basin as
well as small watersheds
developed to quantify the impact of
land management practices
can handle complex watersheds
Associated Model Objectives
Predict the impact of man-made changes
& management practices as well as
natural changes
water, sediment, nutrient and pesticide yields
in complex watersheds with varying soils, land
use and management conditions over a period of
time with accuracy
generate alternate scenarios
Associated Model Objectives
Predict the impact of global warming
on water, sediment, nutrient and pesticide yields
generate alternate scenarios
conduct vulnerability assessment
SWAT (Soil and Water Assessment
Tool) - Model
Features
Physically based
Distributed model
Continuous time
model (long term
yield model)
Uses readily
available data
Used for long
m
ter
impact
studies
SWAT interface in QGIS
SWAT Strengths
Upland Processes:
Comprehensive Hydrologic
Balance
Channel Processes
Flexible Watershed
Configuration
Water Transfer
Physically-Based Inputs
Irrigation
Plant Growth Rotations,
Diversions
Crop Yields
Sediment
Nutrient Cycling in Soil
Deposition/Scour
Land Management BMP Tillage,
Nutrient/Pesticide
Irrigation, Fertilizer, Pesticides,
Transport
Grazing, Rotations, Subsurface
Pond, Wetland and
Streetcomparable
Sweeping
Drainage,
Urban-Lawn
Chemicals,
SWAT variable
to stream
flow is calculated
as sum Impacts
of
Reservoir
Direct surface runoff, Lateral flow (subsurface runoff) from soil profile, GW
flow from shallow aquifer
Model Components
Weather
Surface runoff
Return flow
Percolation
Evapo-transpiration
Transmission losses
Crop Growth
Advantages
physically based
requires generally available information
as input
computationally efficient
capable of being used on
ungauged watersheds
enables users to study long-term
impacts.
Some Salient Features
Pond & reservoir storage
Crop growth & irrigation
Groundwater flow
Reach routing
Nutrient & pesticide loading
Water transfer
HRU creation
HRU created
HRU report
Model Operation
Continuous Operation in Time
Daily Time Step
One Day
Hundreds of Years
Distributed Parameter
Number of Subareas limited only
by Computer memory
Flexible Configuration
Routing Structure
SUBBASIN
ROUTE
ROUTRES
TRANSFER
ADD
ROUTSUB
RECALL
SAVE
Weather - Daily
Precipitation
Max - Min Temperature
Solar Radiation
Wind Speed (Penman-Monteith)
Relative Humidity (Penman-Monteith)
Input or Generate
Temperature - Elevation Lapse Rate
Soil Profile Balance
Percolation
Surface runoff
Lateral Subsurface Flow
Storage Routing Technique
Crack Flow Model
Kinematic Storage Model
ET
Priestly Taylor
Hargreaves
Penman-Monteith
Volume
- Curve no. as function
of soil water
- Green & Ampt - 0.5h
rainfall generator
Peak
- Modified
Rational
- TR - 55
Shallow Aquifer Balance
Recharge - Perc from Soil Profile
Revap - Plant uptake - function of land
use and potential ET
Return flow - Recession constant to lag
flow
Deep Perc - Coefficient * Recharge
Irrigation Withdrawals
Deep Aquifer Balance
No Stream Interaction
Recharge - Deep percolation from shallow
aquifer
Irrigation withdrawals
Sediment Yield
MUSLE
Onstad-Foster
MUST - Based on sediment concentration
Crop Growth
Generic model - Parameterized by
plant database used by EPIC and
WEPP
Phenological Development - Daily heat
unit accumulation
Potential Growth - Interception of
solar radiation (LAI, solar radiation)
Yield - Harvest Index
Growth Constraints - Water, temperature,
Management
Crop rotations - Input max number of
rotation
- max 3 crop within a year
Tillage - Input date and implement 100
implements in database, mixes
residue
Irrigation - Input date and amount,
Automatic based on plant stress
Grazing
Impoundment
Fraction of sub watershed can drain into
pond or wetland
Water and Sediment balance
Channel Routing
Flood Routing - Variable storage Coefficient
Method
Transmission Losses, Evaporation
Sediment Routing
Degradation - Stream Power slope velocity,
channel dimensions, channel erodibility
and cover
Deposition - Fall velocity travel time, flow
depth,
particle size
Reservoirs
ROUTRES Command - Flexible
within routing configuration
Water Balance - Inflow, Outflow,
Evaporation, Seepage, Withdrawals
Outflow
Uncontrolled - Principle &
Emergency spillways
Generic Controlled
Water Management
Transfer - general rules to transfer from any
reach/reservoir to another
Irrigation withdrawals - Specific
reach, reservoir, shallow, deep aquifer
Nutrients
Model tracks movement and transformation
of several forms of nitrogen and phosphorus
governed by nitrogen phosphorus cycle
Nutrients may be introduced to the main
channel and transported downstream
through surface runoff and lateral
subsurface flow
Pesticides
The movement of the pesticide is controlled
by its solubility, degradation half-life, and soil
organic carbon adsorption coefficient.
Pesticide on plant foliage and in the
soil degrade exponentially according
to the appropriate half-life.
Pesticide transport by water and sediment is
calculated for each runoff event and pesticide
leaching is estimated for each soil layer
when percolation occurs
Routing in the Main Channel or Reach
Flood Routing
Sediment Routing
Nutrient Routing
Channel Pesticide Routing
ROUTING
Routing in the Reservoir
Reservoir Outflow
Sediment Routing
Reservoir Nutrients
Reservoir Pesticides
Model Output
Model outputs include all the water balance component
at various levels ie basin, subbasin or watershed level
and at intervals of daily, monthly or annual
surface runoff
evapotranspiration
lateral flow
recharge
percolation
sediment yield
Nutrients
Model Validation
Paleru Subbasin - Krishna basin,
AP
Byrasagara, Kolar
Gandheshwari, Bankura
Karso, Bihar
Cauvery Basin
Krishna Basin
Amameh Catchment - Iran
Thank you
