"Impacts of Hydropeaking on juvenile fish habitats: A qualitative and quantitative evaluation using the habitat model CASiMiR"Extreme fluctuations in daily discharge caused by hydropower plant operations, also known as hydropeaking, are used to cover the peak demands of electrical power. The impacts of hydropeaking on river ecology are well-known and discussed in various literature reviews. This article presents an approach to evaluate qualitatively and quantitatively the impacts of hydropeaking on juvenile fish using the habitat simulation model CASiMiR.
After simulating the basic suitability of juvenile habitats, the influence of sudden flow reduction is additionally incorporated. This is done by defining a threshold time-dependent decrease of the water level which can be tolerated by juvenile fish species. Together with information about the basic suitability and a required minimum water depth, areas with increased risk of fish stranding can be determined. Additional risk areas were identified where the separation of wetted areas from the main stream can also lead to stranding. As long as juvenile fish were able to follow the decreasing water level, the rapid flow reduction and separation of wetted areas may not pose a problem. However the presence of both stranding risks significantly increases the likelihood of mortality for juvenile fishes.
The developed approach was applied in three study sites for juvenile brown trout and bullhead. Based on the results of this approach critical discharge ranges in the operational mode of the hydropower plant could be identified with regards to fish stranding. Furthermore, the results could be used to develop several management scenarios for hydropeaking to optimize the interests of both ecology and economy.