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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Interactions between river morphology and stranding risk due to hydropeaking for juvenile European grayling "

Extreme, short-duration fluctuations caused by storage hydropower plant discharges, or "hydropeaking" occur when hydropower is used to cover the peak electrical loading conditions of a power network. The effects of hydropeaking can result in serious disturbances to the hydrologic regime, the river morphology and the ecological condition of a river. In this study a transient, fuzzy logic based two-dimensional fish habitat model was used to investigate the stranding risk to juvenile European grayling corresponding to different river morphologies. The stranding risk was simulated using two 24 hour discharge hydrographs in two alpine gravel bed river reaches. The chosen reaches had similar proximity to the hydropower plant, but exhibited starkly contrasting morphological features. The spatial distribution of stranding risk was determined based on a multi-step procedure which took into account the stationary habitat suitability, critical dewatering rates and flow depths, but did not include analyses of standing pools separated from the main channel. Although the number of reaches used in the investigation was limited in scope, clear distinctions with respect to the stranding risk were found. The reach with wider, flatter cross sections had a larger amount of stranding risk areas as compared to a reach with a steeply incised channel form. However, stranding risk itself was found to be more a function of a specific set of discharges than a particular rate of change or magnitude of the flow fluctuations. The temporal distribution of stranding risk was found to be almost identical for both reaches.

Keywords: Hydropeaking, Fuzzy-Logic, Habitat Modelling, River Morphology, European Grayling