Runoff and sediment transport from agricultural uplands are substantial threats to water quality and sustained crop production. Farmers, conservationists, and policy makers must understand how landforms, soil types, farming practices, and rainfall affect soil erosion and runoff in order to improve management of soil and water resources. A system was designed and implemented a decade ago to inventory precipitation, runoff, and soil erosion across the state of Iowa, United States. That system utilized the Water Erosion Prediction Project (WEPP) soil erosion model along with radar-derived precipitation data and government-provided slope, soil, and management information to produce daily estimates of soil erosion and runoff at the township scale (93 km2 [36 mi2]). This project has refined the original methodology by using remote sensing techniques and improved databases to accurately determine topography and the spatial distribution of cropping and soil management practices in Iowa. These enhanced parameters along with more detailed meteorological data are used as inputs to WEPP to estimate soil erosion and runoff daily at the hillslope scale. Results are averaged and reported at the scale of small watersheds with an average area of approximately 90 km2 (35 mi2). The revisions constitute a substantial improvement because actual field conditions are reflected, better weather data are utilized, hill slope sampling intensity is an order of magnitude greater, and results are grouped based on surface hydrology. Statistical and comparative evaluations of soil erosion simulations indicate that the sampling framework is adequate and the results are defendable. Various extensions of this work are also proposed.
