Re-establishing fish migration channel of large reservoirs in Jinsha River Basin of China by using an eco-friendly reservoir operation method

Abstract

Study regionA deep reservoir between Xiluodu (XLD) dam and Xiangjiaba (XJB) dam, located in the lower reaches of Jinsha River. Study focusDam construction, especially high dam construction, normally caused the supersaturated total dissolved gas (TDG) downstream of the dam and reduced the flow velocity of the reservoir, which hindered the safe migration of fish. In this research, an eco-friendly reservoir operation model with a multi-objective optimization method was established to reduce supersaturated TDG level and increase reservoir flow velocity in this key ecological zone to restore fish migration pathways. The model consisted of three modules: supersaturated TDG prediction module, reservoir velocity prediction module and multi-objective optimization module. In order to re-establish suitable migratory habitat for fish migration, ecological constraints were added to the reservoir multi-objective operational method including minimum supersaturated TDG level and maximum reservoir flow velocity. And, a 2-D TDG transport diffusion model was adopted to verify the effectiveness of eco-friendly reservoir operation results. The study aims to re-establish fish migration channel of large reservoirs by using eco-friendly reservoir operation methods. New hydrological insightsThe proposed reservoir operation model was efficient in reducing the maximum residence time of supersaturated TDG and increasing the reservoir flow velocity. The area between Xiluodu (XLD) dam and Xiangjiaba (XJB) dam was used as a studying case to analyze the usability of the developed method. The best simulation result was obtained under the scenario with comprehensive consideration of power generation and ecological objectives, and the maximum residence time of 140% supersaturated TDG level was 4 h, which was consistent with the designed worst Mean Lethal Time (LT50) of 4 h for fish. The worst simulation result was obtained in the pattern targeting power generation only, with a maximum residence time of 8 h for supersaturated TDG level at 140%, which exceeded the corresponding LT50 of fish. Under all three scenarios, the XLD hydropower station was generating at full capacity and the minimum flow velocity in the XJB reservoir would be above 0.2 m/s. Overall, this study provides an opportunity to reconstruct the fish migration habitat in the reservoir area.