Document Type


Publication Date

January 1983


Instream flows enhance recreation, hydropower, fish and wildlife maintenance, and riverine ecosytems. Each use has water requirements that vary over time in unique patterns. The determination of the overall instream requirement at any given time must be considered in competition with the demand for municipal and agricultural uses. Two obstacles to integrating instream uses into the appropriation system of water law are difficulty in satisfying the legal requirements of an appropriation for a public use and the fact that instream flow uses are considered more "environmental" than "economic" in character. The extreme options for allocating flow between these user groups are to give them the most junior rights under sppropriative water law and provide instream flows to a desired average, and to give instream flows top priority. Neither extreme is reasonable; the first sometimes allocates no water at all for instream flow in dry years and the second inflicts unnecessarily large burden in terms of benefits foregone on agriculture. A compromist is to reserve some instream flow with senior rights. A stochastic linear programming model was used to estimate the expected benefits foregone to agriculture users. The models provided a framework for maximizing benefits and were applied to various flow levels. A case study application to the Blacksmith Fork of the Little Bear River was based on the instream values beging predominantly recreational with benefit estimates based on user surveys and travel costs. Agricultural losses increased as more senior rights were taken, but the method for providing instream flows made less difference for large targeted flows. The results provide a basis for optimizing instream flow levels, but further methodological development is needed.