Use of Density Current to Modify Thermal Structure of TVA Reservoirs

Abstract

The Tennessee Valley Authority (TVA) reservoirs were innovatively manipulated to prolong strong stratification to keep a nuclear plant's intake water temperature below safety limits. Thermal stratification in a key reservoir was initially stabilized by changing hydropower peaking operation at both ends of the reservoir to precalculated steady releases. Additionally, a predetermined volume of cold water'was released from a deep tributary reservoir and routed as a density current over a distance of more than 160 mi (257 km) through three reservoirs to the subject plant. A mathematical model capable of simulating the flow and thermal characteristics of the reservoir system, including atmospheric heat exchange, was developed to help identify feasible reservoir operation options and to determine the required volume and duration of the cold‐water release. Kinematic and geometric properties of the cold water traveling through the reservoir system were modeled using theories governing two‐dimensional density currents. Accurate determination of travel time and release date was critical to the arrival of cold water at the plant during the period it was most needed.