QUANTIFYING SEDIMENT TRANSPORT PROCESSES, RATES, AND STORAGE IN CHESAPEAKE BAY WATERSHEDS

Suspended sediment transport is an important geomorphic process in Chesapeake Bay, which can also drive delivery of other important materials. transport of nutrients and sediment. Quantifying the lag times between best management practices (BMPs) and desired water quality outcomes require knowledge of the amount of sediment transported and stored and the timescales of transport and storage. We are working at various spatial and temporal scales in watersheds within the Chesapeake Bay to estimate these lag times. This includes the construction of detailed sediment budgets in four watersheds: Difficult Run, Smith Creek, Upper Chester, and Conewago Creek. Age dates of storage reservoirs such as floodplains and in-channel storage features are also being measured to construct age distributions using fallout radionuclides (Pb-210, Cs-137, and Be-7), optically stimulated luminescence (OSL), and radiocarbon dating. We are monitoring sediment storage and radionuclide activities during individual storm events in Difficult Run to investigate short timescales. The information gained from these studies advances knowledge of sediment transport and storage; however, it is not feasible to construct detailed sediment budgets and age distributions in all of the watersheds of Chesapeake Bay. We use the USGS Chesapeake Floodplain Network to obtain spatially extensive and representative data for the Bay watershed. Studies are underway that measure deposition and erosion of sediment and associated nutrients through the non-tidal network, with the goal of identifying predictors of reach- and watershed-scale material fluxes. Fifteen research sites in each of the Valley and Ridge, Piedmont, and Coastal Plain physiographic provinces are instrumented and sampled to measure bank erosion and floodplain deposition over short- (pin method) and long-time scales (dendrogeomorphic method), in-channel sediment accumulation, sediment age dating, associated chemical and physical characteristics of sediment, and reach hydrogeomorphology.