Reservoir Operating Rules to Create Effective Fish Migration Passages in a Reservoir

Abstract Low flow velocity disrupts the potential fish migration passages in a reservoir, and causes reservoirs to become labyrinths for migratory fish. Previous studies showed that fish migration passages in a reservoir can be restored by modifying reservoir operation. However, reservoir operating rules that are specifically designed to support fish migration have not been established, leading to low success for fish migration and high socioeconomic losses. In this research, we established new reservoir operating rules to improve the migration success rate while also reducing socioeconomic losses. Under the new rules, two parameters (reservoir water level and predicted reservoir inflows) were adapted to trigger water releases to open migration passages. The two parameters were optimized by considering hydrological processes, fish migration processes below the dam, the swimming ability of fish, and the socioeconomic benefits provided by the reservoir. We used data from China's Danjiangkou Reservoir to test the effectiveness of the proposed method. We found that the new method can not only improve the migration success rate (from 0.1% to 4.2%), but can also slightly reduce the reservoir's socioeconomic losses (by 3.7%–7.0%). The new method effectively balances the needs of fish migration with the need for socioeconomic development in the areas surrounding dammed rivers.