Implementation of the Revised Universal Soil Loss Equation within a GIS Framework.

Phosphorus and sediment runoff are the primary cause of eutrophication in Cheney Lake, the primary water source for Wichita, Kansas.  Best Management Practices (BMPs) such as no-till farming practices and nutrient management can be implemented to reduce phosphorus runoff on high-risk agricultural fields.  The goal of this project was to use a Geographic Information System (GIS) model based on the Revised Universal Soil Loss Equation (RUSLE) to estimate watershed-scale erosion, prioritize agricultural land for BMP placement, and evaluate existing placement of BMPs within the Cheney Lake watershed.  Field-scale erosion was calculated for the watershed using a RUSLE-based GIS method.  The multiplicative factors which are used in RUSLE were estimated using a variety of spatial data sources and manual data collection.  Fields among the top 20% of estimated erosion rates were considered to be prioritized for BMP placement, under both current (2009) and historical (1997) conditions.   These prioritized areas were used to evaluate past BMP placement, as well as to serve as reference for future BMP placement.  The average annual watershed erosion was estimated to be 317,000 tons given current (2009) conditions.  The erosion based on conditions from 1997 was estimated to be 373,000 tons.  BMPs were implemented on 13% of prioritized field area, and 11% of non-prioritized field area.  Conservation Reserve Program (CRP) fields were placed on 14% of prioritized field area, and 5% of non-prioritized field area.  No-till practices were implemented on 13% of prioritized field area, and 18% of non-prioritized field area.  The top 20% eroding fields were identified given current conditions, and account for approximately 56% of the watershed-wide erosion.  The GIS method has demonstrated utility in evaluating past erosion control measures for the watershed and in informing future decisions concerning BMP placement.