Design of a sediment removal and processing system to reduce sediment scouring potential from the lower Susquehanna River Dams

Abstract

The Conowingo, Safe Harbor, and Holtwood dams located on the Lower Susquehanna River have historically acted as a system of sediment and nutrient pollution traps, retaining and thereby preventing large amounts of ecologically harmful sediment from entering the Upper Chesapeake Bay. However, extreme storm events, termed as scouring events, cause substantial amounts of the trapped sediment to be swept downriver into the Upper Chesapeake Bay, blanketing benthic organisms, affecting subaquatic vegetation growth, and the overall water quality.In addition, all three reservoirs have reached a state of near maximum sediment storage capacity termed as dynamic equilibrium. Based on prior research, this study seeks to reduce the sediment buildup in the LSR Dams through a continuous sediment removal and processing system, and thereby reduce the ecological impact of major scouring events. A set of scour performance curves derived from a regression analysis, and a stochastic lifecycle cost model were used to evaluate the sediment scouring reduction and economic feasibility of three processing alternatives: Plasma Vitrification, Cement-Lock, and Quarry/Landfill, and three removal amount cases: Nominal, Moderate, and Maximum. Since the scour performance curves treat the dams as static, a fluid system dynamics model was used to determine if there is a dynamic interaction between the capacitance of the dams during major scouring events. A utility vs. cost analysis factoring in time, performance, and suitability of the alternatives indicates that a Cement-Lock processing plant at nominal and moderate dredging is the most costperformance effective solution.