ABSTRACT
Four reservoirs in Japan and Switzerland with sediment bypass tunnels (SBT) as strategy against sedimentation were monitored to analyze their effects in terms of up- to downstream morphological and biotic changes. Sediment grain size distribution (GSD), local bed characteristics, microhabitat abundance and invertebrate richness were analyzed. It was found that GSD at reservoirs with newly established SBTs are fine in the up- and coarse in their downstream waterway due to lack of conveyed sediments in the past. Analysis of biotic data directly below the dams reveal that microhabitat richness is low and lentic species abundance is high compared to upstream, while these differences decrease further downstream. Microhabitat and invertebrate richness in the downstream adjust to the upstream values with increasing operation years clearly showing the positive effects of long-term SBT operation.
