SOIL EROSION AND SEDIMENT FLUXES ANALYSIS: A WATERSHED STUDY OF THE NI RESERVOIR, SPOTSYLVANIA COUNTY, VIRGINIA

Anthropogenic forces that alter the physical landscape are known to cause significant soil erosion, which has negative impact on surface water bodies such as rivers, lakes/reservoirs and coastal zone, and thus sediment control has become one of the central aspects of catchment management planning. The RUSLE empirical model, erosion pins and isotopic sediment core analyses were used to evaluate watershed erosion, stream bank erosion and reservoir sediment accumulation rates for Ni Reservoir, in central Virginia. Land-use land cover seems to be dominant control in watershed soil erosion, with barren land and human disturbed areas contributing the most sediment, whereas forest and herbaceous areas were the least eroded. Results shows a 7% increase in human development between 2001 (14%) to 2009 (21%) translating into to an increase in soil loss of 1.45 ton/acre/yr in the same time period. ²¹⁰Pb based sediment accumulation rates at three locations in Ni Reservoir were 0.63, 0.26, and 0.22 g/cm²/ yr, with values decreasing towards the dam, indicating that sediment accumulation and distribution in the reservoir is influenced by reservoir configuration and significant contributions from bedload. All three locations show modern accumulation rate increases. Erosion pin results shows variability in stream bank erosion with values ranging from 5.3 to 11.3 cm/yr. These preliminary results shows that urban growth and the decline in vegetative cover has increased sediment fluxes from the watershed and poses a significant threat to the sustainability of the Ni Reservoir.