Reservoir ecological operation considering outflow variations across different time scales

Abstract

The regulation of reservoirs contributes huge socioeconomic benefits to society at the expense of inducing adverse effects on downstream ecosystems. The reservoir average outflow (such as monthly) can be out of the ecological flow range while the partial daily outflow is suitable due to the outflow fluctuations. To address this issue, the reservoir outflow variations across different time scales (OVDTS) were proposed to form a novel ecological indicator. First, the ecological flow for the full life cycles of indicative native and nonnative species was calculated. Then, the reservoir OVDTS were proposed to describe the streamflow difference between long (e.g., 10-day) and short (e.g., daily) time intervals, and the ecological fitness (namely ecofit) was then formed. Finally, the reservoir operating rule curves were optimized by considering ecofit as well as average annual water supply, water supply reliability, average annual hydropower generation and hydropower generation reliability. The China’s Danjiangkou Reservoir was selected as the case study. It is validated that the established ecofit was almost equal to the proportion of reservoir outflow that met ecological flow range. The ecofit of optimized operating rule curves was improved by 4.19% compared with conventional operation without decreasing the performance of other objectives, also with ecofit improvements of wet, normal, and dry years. It was unexpected that the ecological objective of the optimized operating rule curves was significantly better than that of natural flow mimicry in dry years. The proposed OVDTS and ecofit could be helpful to reservoir ecological operations.