Targeting BMP Placement using SWAT Sediment Yield Estimates for Field-Scale BMPs

Soil erosion from agricultural fields is considered to be a significant contributor of sediment to surface waters in many watersheds across the United States. Black Kettle Creek subwatershed (7,818 ha) of Little Arkansas Watershed (360,000 ha) in south central Kansas was the focus of a innovative project to target conservation practice funding. The SWAT model was used with 10-m DEM topography, SSURGO soils, and a manually developed landuse/ land-cover layer. The calibrated model was used to identify the fields with greatest soil-erosion potential. Fields that had ephemeral gullies were identified by field reconnaissance and included for targeting. Various BMPs (no-till, conservation till, contour farming, terraces, contour grass strips, riparian buffers, and permanent grass), both singly and in selected combinations, were simulated and the effectiveness was determined. The mean BMP effectiveness ranged from 52% to 96% for single BMPs and 85% to 94% for selected combinations of BMPs. Permanent grass produced the greatest average single-BMP effectiveness (96%) followed by Terraces (with contour farming) (78%) and No-till (72%). No-till + Terrace (with contour farming) had the greatest combined-BMP effectiveness (94%). From these field-scale sediment-reduction estimates, payments to implement each BMP for a given field within the watershed were calculated. An in-field signup sheet was developed with field-specific sediment-loss-based payments calculated for each BMP option. This sheet served as a contract with the farmer/landowner for BMP implementation. The farmers/producers in this watershed chose the BMP to be implemented from the list of BMPs that and agreed to maintain the BMP for at least 5 years. The variability of sediment reduction results among fields demonstrated the important influence of site-specific conditions and simulation modeling in estimating soil-loss reductions possible with given BMPs.