Evaluating the Potential Impact of Reservoir Operation on Fish Communities

A developing understanding of instream flow needs now supports maintenance of ecological flow regimes rather than a fixed, time-invariant regulatory minimum flow. This shift is reflected in management of streamflow change created by existing reservoirs and flow diversion structures. With an emphasis on regime-based approaches a new connectivity is demanded between reservoir operations and the resulting downstream flow conditions. Complicating this situation is reservoir management that may be legally limited to flood control and water supply requirements reducing options for supplying downstream needs. This paper proposes an approach to reservoir operation that is based on ecological flow regime concepts. Reservoir operation is guided by six hydrologic indicators selected both to meet the specific flow needs of the local indigenous fish community and to satisfy authorized reservoir operational rules. The approach is based on incorporation of ecology and life history requirements of the fish community in the decision making process to better define and meet flow needs. Optimization using nondominated sorting genetic algorithms provides a basis for reservoir operational schemes that are expected to provide benefit to fish communities downstream while also meeting authorized reservoir storage needs.