Ecological flow restoration

Insights from an experimental flood program on the Spöl River, Swiss National Park

Gabriele Consoli, Christopher T. Robinson (University of Lausanne und Eawag)

The widespread presence of dams in the Alps has deprived most alpine streams of their dynamic character. Alpine streams are naturally subject to strong disturbance drivers where high flow variability and large sediment loads drive environmental conditions. Dams disrupt flow and sediment regimes, modifying the habitat template and the equilibrium between abiotic conditions and biota. This habitat degradation affects the assembly of aquatic organisms, thereby modifying ecosystem function by filtering for specific traits favoured by stable flow conditions. At the same time, the longitudinal fragmentation of the fluvial network isolates local populations, while new flow conditions allows colonization of stream ecosystems by non- native species. Adaptive dam management can make use of experimental floods to restore seasonal peak flows and reintroduce elements of natural disturbance associated with discharge variability as exemplified on the Spöl River. Here, an unprecedented, two-decadal flow manipulation experiment was implemented to restore the river to more normal alpine conditions. Several studies have examined the long- and short- term ecological effects of flow restoration in the system, identifying patterns of response spanning population to ecosystem properties. In this poster, we will give an overview of the most relevant results in light of future applications to other alpine streams.