Determination of optimal operation policy of reservoir with nonlinear model to reduce reservoir water losses

The purpose of this study is to evaluate the evaporation and seepage losses in different dams' reservoirs operation policies. In the present study, in order to assess water losses, water supply deficiency and reservoir efficiency indices from 2012 to 2018, first, the operation policy of the Generalized Reduction Gradient (GRG) formulated, then the mentioned indices for the generalized reduction gradient, the current operation and the proposed rule curve estimated and compared. The Seep/w numerical model calibrated using vibrating wire piezometers to accurately estimate the seepage value. The results showed that the GRG improved the annual seepage, evaporation and deficiency indices by 67.86%, 54.24% and 67.68%, respectively. Moreover, the improvement of the reliability, reversibility, vulnerability and flexibility indices were 368.95%, 110.26%, 67.68% and 4750.40%, respectively. This policy also improved the annual evaporation deficiency indices by 15.88% and 41.86% respectively, compared to the current operation policy. The improvement of this policy in terms of reliability, reversibility, vulnerability and flexibility indices obtained 25.54%, 30.34%, 41.86% and 125.15%, respectively. Interestingly, this policy had an 18.65% growth in comparison to the current operation policy. Therefore, the GRG optimization policy is optimally effective in improving deficiency, evaporation losses, and reservoir's flexibility indices. This approach is recommended to be used for the assessment of reduction in evaporation and seepage losses and deficiency of water supply and also for the enhancement of reservoir performance for other reservoirs.