Water Quality Component Development and Integration with USACE Watershed Hydrologic Models

摘要

Non-point source (NPS) runoff of pollutants is viewed as one of the most important factors causing impaired water quality in freshwater and estuarine ecosystems and has been addressed as a national priority since the passage of the Clean Water Act. To control NPS pollution, state and federal agencies developed a variety of programs that rely heavily on the use of management measures or "Best Management Practices" (BMPs). The main difficulty in selecting appropriate BMPs for a particular site is that BMP effectiveness varies from site to site due to spatial and temporal variations in site specific conditions such as climates, topography, soils, and landuse. This paper describes the development of a water quality sub-model and integration with USACE watershed hydrologic models sponsored by the System Wide Water Resources Program (SWWRP). This integrated modeling system may be used for estimating the site specific effectiveness of BMPs in reducing sediment and nutrient loss from agricultural areas. The water quality sub-model simulates detailed nitrogen (N) and phosphorus (P) cycling at the watershed scale and computes nutrient kinetic fluxes for N and P species. The model consists of three distinct parts: (1) nitrogen and phosphorus cycling in the soil, (2) transformation and loading of nitrogen and phosphorus species in the overland flow, and (3) nitrogen and phosphorus cycling in the stream network. The nutrient sub-model (NSM) integrated with the Gridded Surface Sub-surface Hydrologic Analysis (GSSHA) was tested and validated on three watersheds in Wisconsin (French Run, Eight Mile Creek, and Eau Galle Watersheds). The GSSHA-NSM model performed well in predicting runoff, sediment, nitrogen and phosphorus. This paper presents the model methodology and validation studies currently underway in Wisconsin.