A method for determining the basic ecological flow of riverways through comprehensive hydrology, water conservancy, and habitat simulation analysis

Abstract

[Objective] To ensure the ecological water use of the Yarkand River and scientifically determine the ecological flow rate, [Methods] the area ratio index method based on long-term hydrological data was utilized to calculate the runoff of the studied river section. This approach yielded the long-term runoff result for the control section. Using these runoff calculations and measured cross-sectional information, hydraulic calculation method was applied to obtain hydraulic characteristics such as water depth, wetted perimeter, flow velocity, and water surface width under different flow conditions.To comprehensively determine the ecological flow rate of the section, there are four different method employeel: the Tennant method, the wetted perimeter method, the Q90 method, and the ecological hydraulic method. These method were based on the hydraulic parameters required for fish habitat. Subsequently, the changes in hydrological and hydraulic characteristics of downstream sections under two scenarios: natural inflow and ecological flow discharge.[Results] By comparing and analyzing multiple calculation method, the minimum ecological discharge during the dry season(October to March of the following year) at the Miskni dam site section in the Yarkand River Basin is 10% of the average annual flow, which is 14.3 m³/s. During the breeding season of fish and the wet season(April to September), the ecological flow discharge should be 30% of the average annual flow, which is 42.9 m³/s. Using these ecological flow discharge calculations, changes in the hydraulic parameters of the downstream river section. Compared to the natural inflow in normal years, the flow rate decreased by 79.6%, the flow velocity decreased by 48.3%, the water depth decreased by 31.4%, and the water surface width decreased by 26.1%.[Conclusion] The calculation method for river ecological flow, based on the habitat requirements of fish and combined with hydrological and hydraulic method, is relatively reasonable. It can accurately determine the ecological flow according to the spawning time of fish.However, releasing only the ecological flow in the river can cause significant changes in hydraulic parameters such as cross-sectional water depth, water surface width, and flow velocity. While ensuring the ecological flow for fish, the impact of reduced flow on other animals or vegetation should also be considered.

Keywords

ecological flow / fish habitat / calculation methods / Yarkant River / runoff reductionl / influence factors / water resources