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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING WATER QUALITY IN AGRICULTURAL WATERSHEDS UNDERLAIN BY CLAYPAN AND RESTRICTIVE LAYER SOILS

Location: Cropping Systems and Water Quality Research

Title: SWATing your APEX model: a how-to from the trenches

Authors
item Baffaut, Claire
item Bolster, Carl
item Nelson, Nathan -
item Van Liew, Mike -
item Arnold, Jeffrey
item Williams, Jimmy -

Submitted to: Annual International SWAT Conference
Publication Type: Abstract Only
Publication Acceptance Date: March 27, 2013
Publication Date: July 17, 2013
Citation: Baffaut, C., Bolster, C.H., Nelson, N., Van Liew, M., Arnold, J.G., Williams, J. 2013. SWATing your APEX model: a how-to from the trenches. Annual International SWAT Conference. Session B2, p. 32.

Technical Abstract: Methodologies to link edge-of-field observations to stream loadings need to be developed to integrate what we know of soil and water quality at the field scale to watersheds and river basins. The Soil and Water Assessment Tool (SWAT) can be used to scale up results obtained at field scale with the Agricultural Policy Environmental eXtender (APEX). The APEX and SWAT models are particularly well adapted to this integration because they belong to the same family of models and have many common input parameters. However, they are not identical and the differences need to be recognized before both models can be used jointly. For example, while runoff can be calculated with the Curve Number method in both models, soil moisture routing is different and lead to different soil water content values that affect the curve number, and thus runoff. Similarly, both models can use the MUSLE equation to calculate sediment loss but the soil cover factor is calculated using two very different concepts. This paper reviews the differences in algorithm and parameterization between APEX and SWAT. Since APEX parameterization is more flexible, we define how it can be parameterized so that it becomes equivalent to SWAT, whenever possible. The analysis will help model users separate the model effects from true scale effects when parameterizing these models and interpreting their results.

Last Modified: 12/18/2014