Soil and Water Assessment Tool (SWAT)

Purpose

SWAT was developed to predict the impact of land management practice on water, sediment and agricultural chemical yields in large complex watersheds with varying soils, land use and management conditions over long periods of time.

Description

Soil and Water Assessment Tool (SWAT) is a watershed scale model originally developed by Dr Jeff Arnold for the USDA Agricultural Research Services. It was designed to predict the impact of proposed or alternative land management practices on water, sediment and agricultural chemical yields within complex watersheds of varying soils, land use and management conditions over extended periods of time.

The model operates on a daily time step, it is process based, computationally efficient, and capable of continuous simulation over long time periods. SWAT has the capability of incorporating a number of differing physical processes (major model components) in water shed modelling, these include;

Land Phase of the Hydrologic Cycle

• Climate
• Hydrology
• Soil temperature and properties
• Land cover/plant growth
• Erosion
• Nutrients
• Pesticides
• Bacteria and Pathogens
• Land Management

Also considered is the routing phase of the hydrologic cycle;

• Routing in the main channel or reach i.e. flood routing, sediment routing, nutrient routing channel pesticide routing.
• Routing in the reservoir i.e. reservoir outflow, sediment routing, reservoir nutrients, reservoir pesticides

SWAT - Flow Calibration

 

SWAT is a public domain model actively supported by the USDA Agricultural Research Service at the Grassland, Soil and Water Research Laboratory in Temple, Texas, USA. In modelling a watershed may be partitioned into a number of sub-watersheds which are then further subdivided into hydrologic response units (HRUs) that consist of homogeneous land use, management, topographical, and soil characteristics. The HRUs are represented as a percentage of the subwatershed area and may not be contiguous or spatially identified within a SWAT simulation. Alternatively, a watershed can be subdivided into only subwatersheds that are characterized by dominant land use, soil type, and management.  

This catchment model is able to quantify the impact of land management practices on flow and water quality. As a result the model has widespread use internationally, including New Zealand, in informing land use planning, water quality guide lines and water allocation limits. The only limitation of SWAT then being the quality and amount of input data required to set up modelling on a given catchment study area.

 

Latest Version	SWAT2012 re.664 released December 2016
State of Development	Stable Release
Current Development Activity	Active development by USDA and various research organasations.

Scope

Intended End Users	Specialist modellers supporting land and water managers
Spatial Extents	Unknown
Spatial Dimensions	Unknown
Temporal Resolutions	Days
Temporal Extents	Years, Decades
Steady State or Dynamic	Dynamic

Input & Output Data

Accessibility

Open/Closed Source	Unknown
Licence Type

User Information

Operating Systems	MS Windows
Software Needed	Unknown
User Interface	Please Select
Ease of Use	Moderate
Use in Policy Process	Plan (Policy Formulation), Do (Policy Implementation)
Documentation	SWAT Documentation: https://swat.tamu.edu/documentation/
Support	No formal support. Training workshops are run regularly and there is an annual SWAT conference. Workshops: https://swat.tamu.edu/workshops/ Conferences: https://swat.tamu.edu/conferences/
Users Forum	Forum available

Technical Considerations

Programming Language	Fortran for the main engine code. ArcSWAT is written in a .net language
Methods included for calibration and validation	Calibration tools are provided in the SWATCUP tool from Eawag
Analytical Techniques	Input/output
Model Structure	SWAT Water Movement
Keywords	soil, water, sediment, chemical, land use, land management
Links	SWAT Model Home Page - http://swatmodel.tamu.edu/ An OpenMI compliant version is being developed, see http://www.openmi.org/reloaded/users/compliant-software/SWAT-IHE.html http://www.openmi.org/reloaded/news/OpenMI-Hype-Community.pdf HydroModeller version available. SWAT home page - http://swatmodel.tamu.edu/   SWAT publications: https://swat.tamu.edu/publications/ SWAT theory: https://swat.tamu.edu/media/99192/swat2009-theory.pdf SWAT Calibration/Validation Publications > SWAT: MODEL USE, CALIBRATION, AND VALIDATION. https://swat.tamu.edu/media/90102/azdezasp.pdf SWAT: Soil and Water Assessment Tool https://www.youtube.com/watch?v=AkVG_YccsVI
Key References	SWAT Publications:  https://swat.tamu.edu/publications/ New Zealand SWAT References: Ekanayake, J.C.; Davie, T. (2005). The SWAT model applied to predicting nitrate fluxes in the Motueka catchment. Motueka Integrated Catchment Management Report Series. Landcare ICM Report No. 2004-2005/04. Landcare Research. Lincoln, New Zealand. - http://icm.landcareresearch.co.nz/knowledgebase/publications/public/SWAT_modelling_N-04-05.pdf University of Waikato: LERNZ - Catchment modelling with SWAT- https://www.lernz.co.nz/uploads/swat-fact-sheet.pdf

Associated Case Studies