DESIGNING INSTREAM FLOWS TO SATISFY FISH AND HUMAN WATER NEEDS

The relicensing of nonfederal hydropower projects and the mandated ree valuation of federal water projects require policy makers to balance t he human use of water with instream releases for environmental values, To meet the need for planning level tools for instream flow determina tion, we develop a flexible multiobjective optimization model, The mod el considers both the size and frequency of water supply shortages and the habitat available for fish species as the fish progress through l ife stages. We use a habitat capacity metric to combine expected morta lity, the fraction of a life stage in a particular month, and the area l habitat needs per individual fish. The model incorporates human wate r supply concerns such as monthly variations in human water demand, wa ter-year types, and flood control restrictions. We apply this monthly optimization model to a west-slope Sierra Nevada stream used for munic ipal and agricultural supply and for supporting an anadromous fish pop ulation. Results identified a range of alternative solutions that invo lve trade-offs between water shortage levels and fish population capac ity.