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Title: Improving the spatial representation of soil properties and hydrology using topographically derived initialization processes in the SWAT model

Author
item FUKA, DANIEL - Virginia Polytechnic Institution & State University
item Collick, Amy
item Kleinman, Peter
item AUERBACH, DANIEL - Cornell University
item HARMEL, DAREN - Virginia Polytechnic Institution & State University
item EASTON, ZACHARY - Virginia Polytechnic Institution & State University

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2016
Publication Date: 8/26/2016
Citation: Fuka, D.R., Collick, A.S., Kleinman, P.J., Auerbach, D., Harmel, D., Easton, Z.M. 2016. Improving the spatial representation of soil properties and hydrology using topographically derived initialization processes in the SWAT model. Hydrological Processes. 30(24):4633-4643. doi: 10.1002/hyp.10899.

Interpretive Summary: Accurate characterization of the spatial variation in soils and topography is essential to inform watershed model setup and strongly influences the quality of information provided by the model. We adapt the Soil and Water Assessment Tool (SWAT) using an ArcMap toolbox (TopoSWAT) to spatially adjust soil morphological and soil hydrological attributes across a topographic gradient in USDA-ARS experimental watersheds in Riesel, Texas. This adaptation promises to improve predictions of where and when runoff occurs, thereby improving the model’s ability to inform landscape management decisions.

Technical Abstract: Topography exerts critical controls on many hydrologic, geomorphologic, and environmental biophysical processes. Unfortunately many watershed modeling systems use topography only to define basin boundaries and stream channels and do not explicitly account for the topographic controls on processes such as soil genesis, soil moisture distributions and hydrological response. We develop and demonstrate a method that uses topography to spatially adjust soil morphological and soil hydrological attributes [soil texture, depth to the C-horizon, saturated conductivity, bulk density, porosity, and the field capacities at 33kpa (~ field capacity) and 1500kpa (~ wilting point) tensions]. In order to test the performance of the method the topographical adjusted soils and standard SSURGO soil (available at 1:20,000 scale) were overlaid on soil pedon pit data in the Grasslands Soil and Water Research Lab in Resiel, TX. The topographically adjusted soils exhibited significant correlations with measurements from the soil pits, while the SSURGO soil data showed almost no correlation to measured data. We also applied the method to the Grasslands Soil and Water Research watershed using the Soil and Water Assessment Tool (SWAT) model to 15 separate fields as a proxy to propagate changes in soil properties into field scale hydrological responses. Results of this test showed that the topographically adjusted soils resulted better model predictions of field runoff in 50% of the field, with the SSURGO soils preforming better in the remainder of the fields. However, the topographically adjusted soils generally predicted baseflow response more accurately, reflecting the influence of these soil properties on non-storm responses. These results indicate that adjusting soil properties based on topography can result in more accurate soil characterization and, in some cases improve model performance.