Worth of Inflow Forecast for Reservoir Operation

This study assesses improved benefits that might be gained from the use of long-range streamflow forecasts in the operation of a typical multipurpose reservoir. Long-range is defined as a period of time ranging from one month to one year. The Oroville-Thermalito reservoir system of the California State Water Project (SWP) is selected for study; major benefits to be derived from long-term streamflow prediction for this system are hydropower generation, water conservation for irrigation and/or other beneficial uses, and decreased seepage damage to crops. Flood control benefits are potentially high but those benefits are more amenable to short-term rather than long-term forecasting. Incremental benefits are determined as functions of forecast time and accuracy on the basis of general adherence to current operating rules. The reservoir is theoretically operated over the 1914-73 time period; forecasts and comparisons are based on the historical streamflows. Procedure failure is defined as inability to meet a minimum storage constraint at any time over the 60-year period. To provide an additional evaluation of benefits from forecasting, analyses are also made using the historical means as estimates of future streamflows.