By Susan Jacks, Lana Bean and Robin Kirsch (Tennessee Valley Authority)

Abstract: The Tennessee Valley Authority (TVA) is a multipurpose federal corporation which owns and operates 29 conventional hydropower plants and one pumped storage hydropower plant in the Tennessee Valley. In addition to hydropower generation, the reservoir system provides other beneficial services throughout the Tennessee Valley, including minimum depth for navigation, flood risk reduction, minimum flows for water supply and aquatic habitat, and recreation. TVA uses two different RiverWare models to schedule turbine discharges, spillway releases, power generation, and resulting pool elevations at each of its reservoirs. The first model uses a six-hour timestep and covers a two week planning horizon. Daily scheduled releases from each reservoir provide input to the second RiverWare model, which uses an hourly timestep. This model covers a planning horizon of up to two days and is used to schedule hourly power generation from each hydropower plant. TVA’s optimization model contains a comprehensive list of policy constraints that guide decisions about water releases and pool elevations at each reservoir. Policy constraints are prioritized and must be satisfied to the extent possible before an economic objective function can be maximized. Policy constraints include water supply, navigation, flood regulation, flows for aquatic habitat, recreational flow releases, and special operations. A second RiverWare solution methodology, rulebased simulation, is used following each optimization model run. Rulebased simulation allows modelers to make manual changes to optimization results. Hourly hydropower schedules for the following day and daily average discharges and pool elevations for the upcoming two week period are then distributed to plant operators, recreationists, barge operators, and others throughout the Tennessee Valley.