Impact of Hydropeaking on Fish and their Habitat

ii In the Hasliaare River system, the joint effect of hydropeaking and channelization on young-of-the-year, lake and stream resident spawning brown trout were studied. Steady and dynamic habitat conditions were evaluated and the habitat was modeled for three different degraded morphologies. Specific preference curves for each investigated life stage were developed. Moreover, the reproduction success was monitored by egg to hatching survival experiments and young-of-the-year density surveys. The results show that channelization aggravates the impact of hydropeaking as no young-of-the-year or spawning habitat is present at peak flow. In addition, egg development was found to be impaired. Therefore, the density of young-of-the-year individuals was negligible in the hydropeaking section. The habitat model shows that in a channelized river such as the Hasliaare River, suitable habitat conditions for fish are restrained at peak flow by the riverbed width. Finally, a tool for evaluating scenarios for mitigating the impact of hydropeaking on the downstream ecosystem was developed. The novel economic-ecological diagnostic and intervention method takes into account financial as well as environmental outcomes of hydropeaking mitigation measures for fish habitat improvement. The approach comprises (1) a hydropower operation model of flow regime generation and cost estimates for different mitigation measures, (2) a 2D hydrodynamic model to simulate the flow conditions in representative river reaches, and (3) a dynamic fish habitat simulation tool to assess the sub-daily changes in fish habitat conditions. This modeling approach gives the possibility to estimate true benefits of rehabilitation measures. The intervention diagnostic method was tested on the Hasliaare River. The developed tools and knowledge will help implement scientifically-based solutions for a sustainable hydropower management. The study may help in supporting the application of river restoration projects at existing and newly developed hydropower facilities in alpine areas.