Grundlagenuntersuchungen und Methodikentwicklung zur Bewertung des Wasserkraft-Schwalls bei unterschiedlichen Flusstypen

Due to the disparate characteristics of Austria’s rivers, streams and surrounding riparian areas, similar anthropogenic impacts on our water systems can spark varying reactions. This is also true in the case of those waters affected by hydropeaking. In this context, the specific geometry of the river in question and the potential for “natural development” should be considered the basis for the river’s use as a habitat. These river-type-specific traits and their interplay with hydropeaking processes are at the core of this work, which summarizes the key findings of the SCHWALL_2012 research project. The results show that a river-type-specific and also river-reach-specific assessment of the influence of base and peak flows is essential to effective future river management, as different habitat changes can arise, depending on the respective river morphology and seasonal flow variations. Furthermore, detailed sedimentological studies show that on the one hand the base flow to peak flow ratio does not influence the accumulation of fine sediment in the constantly wetted areas of riverbeds, and that on the other the coarsening of gravel bars can have a major influence on the stranding risk for juvenile fish. With regard to this stranding risk, the findings also show that shallow-water areas display good hydraulic characteristics at both base and peak flow, though, given the habitat they provide for benthic organisms, naturally formed shallow-water areas (e.g. downstream from gravel bars) offer certain advantages over artificially created groin fields. In order to restore rivers and streams affected by hydropeaking, it will be necessary to improve both (a) the hydrological conditions (e.g. ramping velocity) and (b) the morphological situation on the rivers in question (e.g. through restructuring).