Spatiotemporal Water Quality Modeling of Pipeline Water Intake: Lake Gaston, Virginia

Water quality response to reservoir water withdrawal from Pea Hill Arm of Lake Gaston, a non-tidal reservoir tributary with pool elevation changes driven by main lake hydroelectric power plant and other source-sink operations, was examined in this study. The point of water withdrawal in the Pea Hill Arm tributary is located upstream, from the main lake at a location that causes water withdrawal and pool elevation changes in the main lake to influence both the magnitude and direction of tributary flow causing longitudinal velocity null conditions to occur under some conditions. The study focuses on control of withdrawal rate and timing to optimize both quality of water remaining in the tributary and quantity of water that can be safely withdrawn. Research was first conducted assuming steady state conditions and later under spatiotemporal variability experienced in the reservoir with main lake pool elevation fluctuations at the tributary boundary. A source-sink water quality modeling framework using USEPA SWMM and QUAL2E models was developed first to model in-lake water quality in Pea Hill Arm of Lake Gaston under steady state conditions. The initial framework assumed unrestricted downstream flow with negligible affects from a submerged culvert at the interface with the main lake. The affect of hydraulic head across the submerged culvert was also assumed to be negligible.