447 / 2024-03-19 10:21:06

Impact of Layered Water Withdrawal from Cascade Reservoir on Downstream Water Temperature

Xiluodu reservoir; Xiangjiaba reservoir; cascade reservoir; layered water extraction; water temperature

Subtheme 3: Eco-hydraulics and Environment > Topic 3: Eco-environmental Effect of Water Engineering

River water temperature is an fundamental factor for riverine ecosystem as almost all of the physicochemical properties and biological activities are closely related to it. Most reservoir outlets are built in the hypolimnetic layer, which leads to a lower river water temperature downstream of the dam. The ‘cold pollution’ from reservoir hypolimnetic layer has attracted widespread attention as it has modified the life process of many aquatic organisms. By systematically analyzing the water temperature data from 9 hydrological stations and 12 observation sections along the main channel of the Yangtze River, we conducted a comprehensive analysis on the impacts of experimental ecological regulation at Xiluodu and Xiangjiaba cascade reservoirs. Our findings revealed that: (1) The influence of cascade reservoirs on downstream water temperature primarily manifested as low-temperature discharge during spring and high-temperature discharge during winter; (2) Completion of Xiangjiaba reservoir resulted in a delay of approximately 40 days for downstream water temperatures to reach 18°C; (3) Stratified water regulation at Xiluodu reservoir led to an increase in water temperature below the dam by approximately 0.4°C, while having minimal effect on downstream sections influenced by Xiangjiaba reservoir; (4) The elevated temperature (1.8°C above the mainstream average), substantial water volume (accounting for 45%) from the Minjiang River, and temperature rise along the mainstream of the Yangtze River are the primary driving factors behind the increased water temperature along the Xiangjiaba-Zhutuo section within the protected area. The proposed research methodologies and findings can serve as a valuable reference for comprehending reservoir operation's impact on water temperature structure, while also providing a scientific basis for subsequent optimization of ecological scheduling schemes.