Impacts of hydropeaking and thermopeaking on the downstream habitat in the Dal River, Korea

Dams located upstream only release water during the period of hydropower generation. This induces short-term fluctuations of water discharge in the downstream reach, which is called hydropeaking. As occurs quite often, if the temperature of the water released form the upstream dam is different from the water that is flowing in the downstream reach, the water temperature also tends to show short-term fluctuations, which is called thermopeaking. This study investigates the impacts of both hydropeaking and thermopeaking on the downstream habitat. The study area is a 2.3 km long reach located downstream from the Goesan Darn in the Dal River, Korea. To assess such impacts, this study conducted physical habitat simulations. The CMS-Flow model was used for the computation of the flow and water temperature, and the GEP model for the habitat simulation. Three physical habitat variables, flow depth, velocity, and water temperature, were used. The Zacco platypus was selected as the target fish in the study area. Simulation results indicated that the hydropeaking flows significantly reduced both the CSI and the WUA when compared with the natural flow regime. In addition, the use of the water temperature in the physical habitat simulations further decreased both CSI and WUA, indicating that thermopeaking is as important as hydropeaking in this type of assessment.