2. Predicting Sediment and Phosphorus Delivery with a Geographic Information System and a Computer Model M.S. Richardson and A. Roa-Espinosa; Dane County Land Conservation Department; Dane County, Wisconsin, USA Introduction: Excessive amounts of sediment and phosphorus in surface water, negatively impact its aquatic and wildlife habitat, recreational use, and aesthetic qualities. Sources of sediment and phosphorus include both agricultural and urban land uses. To maintain or improve water quality, local, state, and federal agencies are identifying sources of sediment and phosphorus and predicting their delivery to receiving waters. Objectives: Our objectives were to predict sediment and phosphorus delivery for the Upper Sugar River Watershed (a 443-km 2 watershed in southern Wisconsin) by: 1. developing a Geographic Information System (GIS) database for the study area; 2. using the GIS data as inputs to WINHUSLE, a distributed parameter, water quality computer model based on the Universal Soil Loss Equation (USLE). Methods: The WINHUSLE (Wisconsin Nonpoint Hydrologic Universal Soil Loss Equation) computer program was run in R:BASE (a relational database) using nine R:BASE tables. Three tables already existed from a federal soils database. Six new tables were created from watershed specific data, most using GIS data layers. The three major GIS data layers used were: 1. Land use/Land cover 2. Soils (by soil map unit) 3. Digital Elevation Model (DEM) The land use and soils layers were combined to create USLE factors (see Figure 1). The DEM was used to generate a digital drainage area data layer. Inputs for WINHUSLE from the USLE, drainage area, and overlay of USLE/drainage area data layers were downloaded into ASCII files. Finally, the files were imported into R:BASE, calibration R:BASE tables were adjusted, and WINHUSLE was run. Study Area: State of Wisconsin, USA Sugar River Watershed in Dane County Wisconsin Canada Sugar River Watershed Lake Belle View is a shallow lake created from a dam at the lowest point of the Sugar River Watersheds in Dane County. It has several water quality problems usually associated with impoundments including: sedimentation, turbidity, excessive rooted aquatic plants and attached algae, and free floating bluegreen algae to name a few. We hope the results of our study will be used to reduce the amount of sediment reaching the lake and thus address lake water quality problems without resorting to costly dredging. Mexico Dane County Land Conservation Results and Discussion: The WINHUSLE model estimated that the outlet of the Sugar River Watersheds (located at Lake Belle View) receives ~6,700 MT of sediment and 20,000 kg of phosphorus per year. Sediment delivery was also calculated across the landscape and results were used to identify areas with relatively high delivery. These areas can be examined in the field, and management practices (including conservation tillage, buffer strips, terraces, or water and sediment control basins) can be implemented to reduce sediment delivery. Combining GIS data with a computer model was an effective and efficient method to acquire sediment and phosphorus deliveries for a large area (443-km 2 ). The most time consuming process was the creation of a digital land use layer; however, this layer can be used in other applications. Although model results were not compared with monitored values in the Sugar River Watershed (due to lack of data), WINHUSLE sediment and phosphorus numbers have been shown to reflect monitored data in other watersheds in Dane County. Figure 1. Flow chart of data used to run WINHUSLE. Land use / Land cover Soils (K factor) Hydrologic Drainage Areas Cumulative Sediment Yields Sediment Delivery by Field The water quality of the Upper Sugar River may be threatened by agricultural and increasing urban runoff in the watershed. An example of a brown trout that could be found in the Sugar River Watershed. Poster printed February 1999. † Universal Soil Loss Equation A = R*K*LS*C*P A - soil loss rate (MT/ha) R - annual rainfall factor K - soil erodibility factor LS - slope length/slope gradient factor C - land cover/cropping management factor P - erosion control practice factor To run WINHUSLE, the watershed must be sub-divided into hydrologic drainage areas -- at a minimum, at the confluence of every stream. We used a DEM to divide our watershed into 504 drainage areas approximately 0.9-km 2 in size. K factor or soil erodibility represents the ability of the soil to resist erosion. It is a function of the surface soil texture and composition. Note that the LS factor (slope length/slope gradient factor) is also based on soil information but is not displayed. WINHUSLE generated both sediment and phosphorus yields (only sediment is shown) for each field or land use to the outlet of the hydrologic area(s) that it’s in. WINHUSLE generated both sediment and phosphorus yields (only sediment is shown) for each of the 504 hydrologic drainage areas. Funding for this project was provided by the Wisconsin Department of Natural Resources and the U.S. Environmental Protection Agency. Digital Elevation Model (DEM) The Digital Elevation Model used had a vertical elevation to the nearest 0.3 meter for every 10 meters on the ground. Roads City/village zoning Wetland s Census land use Farm fields Land use/ cover Soils DEM Farm field database USLE factors † Hydrologic unit data Run WINHUSLE Sediment and phosphorous delivery results WINHUSLE inputs