APPLICATION OF SOIL AND WATER ASSESSMENT TOOL (SWAT) TO MODEL THE IMPACT OF PROGRESSIVE LAND-USE CHANGES ON SEDIMENT AND NUTRIENT FLUXES IN RIVANNA RIVER BASIN, VIRGINIA, USA

The Chesapeake Bay, on the eastern coast of both Maryland and Virginia has been the subject of intense research for its persisting degrading environmental conditions. Among the most prominent causes of this ecological decline is sediment and nutrient pollution. While there have been numerous attempts to clean up the Bay, understanding the dynamics of the sub-watersheds that drains into the bay is crucial in determining the course of actions needed to remediate this important ecosystem. This study aims to understand and estimate the sediment and nutrient fluxes into the Rivanna River Basin, a sub-watershed of the James River using The Soil and Water Assessment Tool (SWAT) model. This nearly 2000 km² sub-watershed begins in the Blue Ridge Mountains of Virginia, and flows through the city of Charlottesville before joining the James River. The goal is to create a viable model for predicting the transport of soil/ sediments and associated nutrients through the Rivanna River. The SWAT database was created using soil characteristics, land-use and cover, climate, elevation, water flow and nutrient data. This model was then calibrated and validated using available 1994 to 2003 data. Preliminary results modeled using present watershed conditions suggest that sediment fluxes of 11,500 tons/year occurring within Rivanna River watershed. The progressive conversion of natural forest and wetlands to urban and agricultural areas in this watershed characterized by steep slopes is likely to significantly increase over the estimated sediment flux rates. The model might also be overestimating the sediment trapping efficiency of a dam placed upriver of Charlottesville on the South Fork of Rivanna River. Improved model calibration, historical land-use and cover data and projected future changes will be used in a time series model output to enhance understanding of temporal variation of both sediment and nutrient fluxes into Rivanna River.