SUSPENDED-SEDIMENT YIELDS IN THE CHESAPEAKE BAY WATERSHED (1952-2001)

Excess sediment is having an adverse effect on the habitat of the Chesapeake Bay and its watershed. This research identifies the major sediment-producing areas in the Chesapeake Bay watershed so that an understanding of sediment transport can be developed. Average annual suspended-sediment yields measured at 65 U.S. Geological Survey streamflow-gaging stations ranged from 2.9 to 827 t km-2 y-1. Suspended-sediment yields were averaged for stations in the 9 major watersheds draining into the Chesapeake Bay and showed that sediment stations in the Potomac River watershed (n=13) had the highest average annual suspended-sediment yield (113 t km-2 y-1), followed by sediment stations in the Susquehanna River watershed (n= 36; 87.2 t km-2 y-1).

Three of the four highest average annual suspended-sediment yields were recorded in small watersheds draining to the Potomac River near the Washington, D.C. metropolitan area (Snakeden Branch at Reston, VA; Smilax Branch at Reston, VA; and Northwest Branch Anacostia River near Colesville, MD) that operated for different years from 1972 through 1978. These high sediment yields may reflect suburban construction activities occurring in the Washington, D.C. metropolitan area. The highest average annual suspended-sediment yield in the Chesapeake Bay watershed was at Little Conestoga Creek near Churchtown, PA from 1985-92 (827 t km-2 y-1), which drains to the Conestoga River, a tributary of the Susquehanna River. The average annual suspended-sediment yield for four stations in the Conestoga River watershed, which operated at different times from 1985 to 2001, were averaged and showed an annual suspended-sediment yield of 279 t km-2 y-1.

Contributing areas for the 65 sediment stations were categorized into six physiographic regions (Coastal Plain, Valley and Ridge, Piedmont, Mesozoic Lowlands, Blue Ridge, and Appalachian Plateau). The average annual suspended-sediment yields for watersheds draining each province were averaged and showed that watersheds that had a majority of their contributing area designated as Piedmont (n=17), had the highest average annual suspended-sediment yield (23.3 t km-2 y-1). Watersheds that had a majority of their contributing areas draining the Coastal Plain (n=4) had the lowest average annual suspended-sediment yield (0.6 t km-2 y-1). Future studies will address the influence of land use on erosion and sediment yields.