Modeling Total Dissolved Gas for Optimal Operation of Multireservoir Systems

Abstract

One important environmental issue of hydropower in the Columbia and Snake River Basins (Pacific Northwest region of United States) is elevated total dissolved gas (TDG) downstream of a dam, which has the potential to cause gas bubble disease in affected fish. Gas supersaturation in the Columbia River Basin primarily occurs due to dissolution of bubbles entrained during spill events. This paper presents a physically based TDG model that can be used to optimize spill operations in multireservoir hydropower systems. Independent variables of the model are forebay TDG, tailwater elevation, spillway and powerhouse discharges, project head, and environmental parameters such as temperature and atmospheric pressure. The model contains seven physically meaningful experimental parameters, which were calibrated and validated against TDG data collected downstream of Rock Island Dam (Washington) from 2008 to 2012. A sensitivity analysis was performed to increase the understanding of the relationships between TDG downstream of the dam and processes such as air entrainment, lateral powerhouse flow, and dissolution.