Minimum instream flow requirement for the water-reduction section of diversion-type hydropower station: a case study of the Zagunao River, China

Abstract

Diversion-type hydroelectric exploitation can reduce instream flow and destroy river ecosystem continuity. Maintaining instream flow is considered an effective way to remediate the damages. The Physical Habitat Simulation (PHABSIM) system still probably remains as the most widespread habitat method used to establish instream flow standards or to link habitat variations with fish population dynamics. This study applies the PHABSIM models, which create a habitat–flow relationship, describing the physical habitat suitability of alternative instream flow releases. Selecting the water-reduction section of the Sangping Power Station on the Zagunao River as the research object, the hydraulic pressure at a cross section was obtained through habitat simulation. The Cyprinidae family of fish, dominant in this region, was targeted using velocity and depth suitability curves. The quantitative relationship between flow and suitable habitat area was established, with the minimum instream flow of the study area calculated as 30.0 m3/s, according to the weighted usable area–flow curve. The minimum instream flow of the study area was also estimated through common hydrologic and hydraulic methods. The resulting comparison indicated that the habitat simulation model achieved very similar results to those of the wetted perimeter method and achieved between “good” and “very good” levels using the Tennant method. The result indicates that the PHABSIM model is useful for optimizing the flow release schemes of hydropower stations in southwestern China. Moreover, it helps to analyze trade-offs between human and environmental water needs, resulting in solutions that minimize ecological integrity disturbances.