SWAT: Soil & Water Assessment Tool

Created and primarily maintained by Jeff Arnold, USDA-ARS, Temple, TX.

Used locally and presented by Tamie Veith, USDA-ARS, State College, PA

SWATSoil & Water Assessment Tool

Nonpoint source simulation model Hydrologically-driven Continuous time-step Divides watershed into HRUs w/in subbasins

HRU = hydrologic response unit = soil/landuse/slope units

Routes by subbasin

Input Data – widely available DEM – usually 10 or 30 meter Soil survey – SSURGO Basic land use – PAMAP Stream network and outlet point

– USGS, aerial photo, blue line stream Precipitation (daily or breakpoint)

Min, max air temperature Humidity, solar radiation, wind speed

Streamflow (m3/s) – for calibration

OPTIONAL

Input Data – harder to quantify

Field boundaries Rotational land use and management BMPs

placement, maintenance, lifespan Stream quality – for calibration

Sediment, N, P, chemicals (atrazine) Biochemical oxygen demand, dissolved

oxygen, algae, coliform bacteria

Output -- Environmental Stream reach and outlets

Stream flow Sediment, N, P, chemicals (atrazine) Biochemical oxygen demand, dissolved oxygen, algae,

coliform bacteria

Crops # days water, nutrient stressed Biomass, yield, evapotranspiration

Overland Water movement - surface, lateral, groundwater Erosion Nutrients – surface, leaching, soil Mass water balance

Output – Land management

By careful pre- and post processing and deduction.

Output – Regulatory, economic

NONE

End User

Researcher or simulation modeler for conservationists and policy makers

Software

SWAT http://swatmodel.tamu.edu Free

ESRI ArcGIS Desktop w/ Spatial Analyst http:// www.esri.com ArcEditor: $7000 ArcView: $1500 Spatial Analyst: $2500 GIS viewers: freeUniversity or Agency may have site license

Training

SWAT modeling 2 day workshops $500 each yearly in TX

SWAT data processing 1 day workshop $200

ArcGIS online tutorials 1 to 3 day workshops free to $500/8hr sites around US

Also may be available through university

Scale of Relevance

Watershed+ within-field variability

+ topography+ soils

+ detailed land management+ hydrology / nutrient losses

+ individual fields+ watershed

USDA / ARS

BMP placement: Farm-level

Crop rotations & contour strip crop

Crop rotations & nutrient management plans

Contour strip crop & nutrient management plans

Nutrient management plans

Riparian forest buffers None

Basic Optimal

BMP placement: Watershed-level

Same P loss, 30% cheaper

Assumptions / Limitations Limited surface routing Daily rainfall by volume

Intense or 2-day storms can be muted

Best for long-term, steady-state predictions Underpredicts low-flow and extreme event volumes

Stream model, QUAL2E Steady-state, 1-dimensional flow and water quality in

well-mixed streams

Farm 4

Farm 3

Farm 1

Farm 2

No natural flow boundaries

Other boundaries: economic, social, political

Adjacent fields managed differently

Down stream water quality impacts

Boundaries Seldom Coincide

Whole Farm Approach

USDA / ARS

IFSM: Integrated Farm System Model

Whole farm simulation modelDriven by farm production Process-basedDaily time-step Evaluated seasonally or annually Output to end user is average annual with

standard deviation

Created and maintained by Al Rotz, USDA-ARS, State College, PA

Integrated Farm System Model

Input Data Crop type, rotation, quality management practices, timing, machinery storage facilities and selling strategy

Animal type, housing, feed, replacement strategy management equipment and facilities manure management

BMP / alternative management scenarios Cultural/social considerations

Output -- Environmental Surface runoff and sediment from farm N overland, leached, volatilized, soil balance

P overland in runoff or sediment-bound, soil balance

K overland, soil balance

Ammonia, & greenhouse gas emissionsDairyGHG & DairyGEM – Emission predicting models. Use same processes but less user input.

Output – Farm management Crops # days water stressed, biomass, yield, CP, NDF

Animals production, replacement, rations fed

Output – Economic All production costs Labor, machinery, facilities, feed/bedding/fertilizer/fuel Net return to farm

End User / Training

Researcher, conservationist for the farmer or policymaker

Farmer is most knowledgeable about inputs and best farm representation

BUT model is largely a researcher tool No HELP desk

DairyGEM is more user-friendly

Software - Free http://www.ars.usda.gov/Main/docs.htm?docid=2708

Scale of Relevance

Farm crop growth feeding strategies milk production farm profitability nutrient balances

off-farm nutrient losses

Compare farm-level effects of manure application methods

Precision management

Parameters ID

Farm net return 1

Purchased feed cost 2

Seed, fertilizer cost 3

Machinery cost 4

Total production cost 5

Milk and animal income 6

Sed-P loss from corn 7

Sed-P loss from the farm 8

Sediment loss from corn fields 9

Sediment loss from the farm 10-90% -60% -30% 0% 30%

10

9

8

7

6

5

4

3

2

1

-90% -60% -30% 0% 30%

10

9

8

7

6

5

4

3

2

1

• 4 ha increase in corn area• 5% increase milk prodn. • No till

•12 ha small grain • No till

0.3-0.1

-2 -1 0 1 2

P balance

Assumptions / Limitations

Not strictly continuous Infrequently harvested grasses difficult

Dairy, beef, or crop farms Corn, soybean, small grain, alfalfa, grasses

No spatial placement within farm

No split management on same crop

USDA

Pasture Systems and Watershed Management Research Unit

Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.

Agricultural Research Service

USDA / ARS

USDA Model Descriptions

USGS Surface Water and Water Quality Models Information Clearinghouse http://smig.usgs.gov/SMIC/SMIC.html

Some ARS Software and Datasets: http://www.ars.usda.gov/services/