Impact of hydropeaking on downstream fish habitat at the Goesan Dam in Korea

Abstract

AbstractThe impact of hydropeaking on downstream fish habitat was investigated. The study area is a 2.3‐km long reach of the Dal River, located downstream from the Goesan Dam, Korea. Such short‐term effects of hydropeaking as flow unsteadiness, down‐ramping rate, transport of benthic macro‐invertebrate, and changes in composite suitability index (CSI) and weighted usable area (WUA) were examined. To assess the change in CSI and WUA, physical habitat simulations were carried out. The 2D unsteady flow model and the habitat suitability index model were used for hydraulic and habitat simulations, respectively. Zacco platypus was selected as a target species of the study area. Hydraulic simulations showed that flow depth changes rapidly with time at the rising and falling stages of discharge due to hydropeaking, and this impact propagates with time. The down‐ramping rate was found to decrease gradually in the downstream direction, implying that the fish can be stranded in the 1.5‐km upstream reach. In addition, simulation results indicate that the transport of macro‐invertebrate may occur in the riffle, and the hydropeaking flows increase slightly the area of possible transport of macro‐invertebrate compared with the normal flow. However, catastrophic drift will not occur due to hydropeaking flows. The results of physical habitat simulations revealed that the hydropeaking flows decrease the CSI, although the river morphology affects the CSI to some extent. Regarding the WUA, the overall habitat quality in the entire study reach was found to decrease due to hydropeaking.