Design of a dam sediment management system to aid water quality restoration of the Chesapeake Bay

Abstract

The water quality of the Susquehanna River, a major freshwater tributary of the Chesapeake Bay, significantly affects the aquatic health of the Bay. Following major storms in which the river flow rate exceeds 300,000 cubic feet per second (cfs), nutrients and sediment stored in the Lower Susquehanna Reservoir are deposited into the Chesapeake Bay. These excess nutrients facilitate algae blooms that hinder the growth of sub-aquatic vegetation (SAV) and harm the Bay's aquatic species. The Conowingo Dam, on the Lower Susquehanna River, is estimated to be at 85% of its sediment capacity. To reduce the sediment backlog, three dam sediment management alternatives have been identified: (i) No Mitigation, (ii) removal of sediment by Hydraulic Dredging and (iii) removal of sediment byHydraulic Dredging and increasing the bottom shear velocity to avoid sediment build-up. A utility analysis conducted using a fluid mechanics, ecological impact and business model indicates annual removal of sediment at 5,000,000 cubic yards to produce slag product, with the instantiation of a flow diverter to increase bottom shear stress to be the best alternative.