Unstructured block ramps – River Kander / Simme case study

During the past few decades about 20 sills have been built to stabilize the longitudinal profile at Kander and Simme, two typical pre-alpine rivers of canton Bern. Due to the drop height of those sills, which are between 0.70m – 3.5m, fish and aquatic communities are unable to pass them. Unstructured block ramps were chosen as a possibility for rebuilding the longitudinal cross-linking between different sections on both rivers.

In comparison to structured block ramps such as those at the Emme river, the blocks in this type of block ramp are not grouped to special configurations, instead they are loose unstructured distributed on the rough-textured bed material (Fig.1, Fig.2). Based on the research studies of Whittaker et.al. (1998) on unstructured ramps the model laboratory experiments are in progress. Four different slopes (0.5 %, 1 %, 2.5 %, 5 %), three different block placement densities (10 %, 15 %, 20 %) and two weightiness of blocks (2 t, 3 t) are tested. Additionally the influence of sediment input rate on the ramp stability will also be progressed in several tests.

The research will show in which circumstances the qualifications will not be fulfilled.