Soil Water Assessment Tool (SWAT) Model Input

Assefa Melesse

SWAT features

• Physically based– Needs basin-specific data on “...weather, soil

properties, topography, vegetation, and land management practices...”

– Benefits:• Ungaged watersheds can be modeled• Sensitivity to different input data can be quantified

• Uses readily available inputs– GIS sets often already compiled by different agencies

• Computationally efficient– Even for very large basins

• Determines long-term impacts– SWAT is a continuous time model

SWAT

MODEL OBJECTIVE

• Predict the effect of management decisions (Climate and vegetative changes, reservoir management, groundwater withdrawals, water transfer) on water, sediment, nutrient and pesticide yields on large, ungaged river basins.

MODEL COMPONENTS:

• Weather, surface runoff, percolation, ET, transmission losses, pond & reservoir storage, crop growth & irrigation, groundwater flow, reach routing, nutrient & pesticide loading, water transfer

SWAT Model Input

INPUT DATA:• Physical

– Elevation, Land cover, soil • Weather

– Rainfall, air temperature (Min and max), solar radiation, wind speed and relative humidity

• Hydrological – Stream flow, sediment and nutrient delivery data

• Non-point and point source pollution data– Fertilizer and pesticide application data– Point source of pollution

SWAT Database

SWAT Model

INPUT DATA:• DEM:

– SRTM (90m) from USGS or other sources (http://seamless.usgs.gov/)

– Watershed delineation

– Stream network and confluences

– Entering point sources

SWAT Model Input: Elevation

SWAT Model

INPUT DATA:• Land cover

– Landsat-derived (Level I?) data

– CN, manning’s coefficient

– land cover/land use map will need to be

reclassified into SWAT land cover/plant types.

– Three options

SWAT Model Input: Land cover

SWAT Model Input: Land cover cont.

1. to use USGS category codes when creating the map (or use a USGS land use/land cover map).

2. to select the SWAT land cover/plant type or urban code for each category

3. to create a look up table that identifies the 4-letter SWAT code for the different categories of land cover/land use

SWAT Model Input: Land cover cont.

SWAT Model Input: Soil

• Runoff, infiltration, sediment and anion exchange

• 1: 5M vector (Source: http://www.isric.nl/)

• The user will import SWAT soil files (.sol) or type the soil data into the User Soils database for each of the map categories prior to creating the project.

SWAT Database: Soil cont.

SWAT Model Input: Weather

• Rainfall, solar radiation, air temperature, humidity and wind speed

• Major input for hydrology, sediment and chemical transport

• ET• Source: Weather station data from each island

• Each weather station location will be entered with the corresponding data

SWAT Database: Weather cont.

• Fertilizer and pesticide data

• Large number of names of fertilizer and pesticide in the SWAT database

• New chemicals can be entered

• Allows if manure is used in the application

SWAT Model Input: Chemicals

SWAT Database: Fertilizer

SWAT Database: Pesticide

Discussion