Investigation of hydropeaking impacts on river ecology following the swiss guidelines - experiences and insights.

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Matthias Schneider

Friday 3 july 2015

8:30 - 8:45h at Europe 1 (level 0)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 14G. Environment - Renewable

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Hydropeaking is one of the major impacts on river ecology in the alpine region. It occurs mostly downstream of storage hydro power plants due to their operation that is adapted to energy demand. During periods with high energy demand the water stored in a reservoir is discharged through turbines, during periods of low energy demand flow is on a much lower level. This fast and intense change of discharge causes temporally and spatially highly variable conditions for fish. In Switzerland in 2012 a guideline has been released defining indicators for the assessment of hydropeaking impacts on fish such as stranding of young fish and deterioration of spawning grounds. The methodology has been applied in a catchment in southern Switzerland. Several reaches with different morphological features have been selected and different scenarios of hydropeaking operation have been studied. Is has been shown that instationary 2D hydrodynamic calculations are required to define a reliable basis for the achievement of the indicators. Differences between steady and unsteady modelling have a strong impact on the risk of fish being trapped in shallow water that is represented by one of the indicators. The assessment of spawning grounds is affected by the kind of hydrodynamic calculations and their evaluation.Sediment movement is one of the main risk factors for the functionality of reproduction areas. Investigations indicate that peak flow is not necessarily the most critical situation for the assessment. Results and recommendations for the future investigations of hydropeaking impacts are presented.