UC Santa Barbara

This research quantifies the impact of lake evaporation and rainfall on optimal reservoir capacity and water yield. A reservoir design and operation model was developed and applied to the Santa Ynez River basin of central California, which endures large evapotranspiration and extreme climatic variability. Reservoir design and average annual water yield were obtained in two cases. First, lake evaporation and rainfall fluxes were taken into account in the water balance of the reservoir system. Second, those same fluxes were ignored. The optimization-model results indicate that in-lake hydrology plays a considerable role on estimates of optimal reservoir capacity and yield. Furthermore, results indicate that the lack of proper consideration of in-lake hydrology leads us to err on the side of greater risk. Specifically, reservoir capacity and average water release are under and overestimated, respectively. The optimization model is particularly well-suited for modeling reservoir systems with active in-lake hydrologic fluxes and allows a variety of objective functions to be considered, thus, providing flexibility in the optimization of reservoir design and operation.