Research on the impact of hydropower plant operation on fish habitat at the reservoir tail

Abstract

[Objective] The operation of hydropower plants not only alters the suitability of downstream river habitats through changes in discharge but also affects the habitat characteristics of the fluctuating backwater area at the reservoir tail due to water level fluctuations in front of the dam. By clarifying the effects of hydropower plant operation on the suitability of fish spawning habitats in the backwater area under different water inflow conditions, this research aims to provide a reference and guidance for ecological scheduling during fish spawning periods in regulating hydropower plants. [Methods] Using the operational data from the Longyangxia hydropower plant in the upper Yellow River as a case study, this research focused on the Yehuxia spawning ground at the reservoir tail as a fish protection habitat. Platyharodon extremus was selected as the target species. A fish habitat model was constructed, and the Weighted Usable Area(WUA) and the Splitting Index(SPLIT) were introduced to quantitatively assess how changes in hydropower plant scheduling affect habitat suitability during fish spawning periods. [Results] The result indicated that the current annual operational mode affected the fish habitat at the reservoir tail, with the WUA first increasing and then decreasing, while the SPLIT of the spawning habitat gradually increased. From early April to late May, the WUA increased by 74.43%. From late May to late June, the WUA decreased by 52.39%. From April to June, the SPLIT increased by 221.94%. The inconsistent trends of WUA and SPLIT were due to the fact that WUA reflected changes in the spawning habitat area, while SPLIT represented the integrity and fragmentation of the spawning area. From early April to late May, increases in flow and decreases in water level expanded the spawning area. However, changes in topography and flow patterns worsened the overall integrity, causing both WUA and SPLIT to increase. From late May to late June, as flow levels continued to rise and the reservoir water level increased, the suitable spawning areas shrank and became more fragmented, leading to a decrease in WUA and an increase in SPLIT. [Conclusion] The result indicate that the annual operational mode at Longyangxia significantly affects both SPLIT and WUA. Further ecological scheduling of the hydropower plant can effectively improve the ecological hydrological processes and hydrodynamic conditions of fish spawning habitats in the reservoir tail backwater area.

Keywords

hydropower plant scheduling / reservoir tail backwater area / fish habitat suitability / weighted usable area / splitting index / influencing factors