A project was undertaken to develop mathematical models capable of incorporating elements of risk and uncertainty into the solution of optimal water resources systems designs. The basic premise is that risk taking is an acceptable economic alternative, so that it may be feasible to design a somewhat inadequate system. Simulation and some optimization techniques were used. The data base was the Twin Buttes reservoir on the South Concho River in Texas. A study was included of farmers' reactions to possible uncertainties in irrigation water supply.