Development of a Decision Support Tool for Determining Optimal Hydropower Dam Operations in a Southeastern United States Tailwater

Since the construction of Tims Ford Dam (TFD) in 1970, the Elk River in Tennessee and Alabama has experienced substantial changes in downstream hydrothermal and hydrological conditions. These changes have inhibited the ability of some native species to persist in affected reaches, including the federally endangered Boulder Darter Etheostoma wapiti. Cold, hypolimnetic releases also have allowed for the development of a recreational trout fishery downstream of TFD. In 2007, the Tennessee Valley Authority ceased hydropower generation from April – October in order to (1) enhance survival and recruitment of existing Boulder Darter populations, (2) promote recolonization of Boulder Darters into previously unsuitable stream reaches, and (3) maintain conditions suitable for the persistence of Brown Trout Salmo trutta and Rainbow Trout Oncorhynchus mykiss in a 15-km reach downstream from TFD. Using a structured decision making approach, we developed a decision support tool to aid managers in identifying the operational scenarios for TFD that will meet these objectives. The decision model was parameterized using a combination of ecological models, simulations of Boulder Darter responses to alternative operational scenarios, changes in the trout fishery resulting from alternative operational scenarios, and stakeholder values associated with ecological outcomes and decision alternatives.