Linth 2000 - Physical experiments to analyze morphological aspects of a local river expansion

In the context of the project "Linth 2000" the VAW is assigned to examine the consequences of a newly planned river expansion in the Escherkanal on the stability of the existing dams, in order to ensure flood protection for the Linthebene, where several villages are located. The Escherkanal is located close to Chli Gaesitschachen 1,5 km before it is connected to the Walensee.

The river sediment in the reach is characterized by a pronounced armouring layer, with significant differences in the grain size distribution, compared to the deeper sediment, which would lead to a strong non-uniformity in the grain size distribution in the new river expansion section. To cover this problem a hydraulic model has been built on a 1:40 scale, leading to a total length of the model of 34 m. The model is equipped with a movable bed and constant sediment supply during the experiments. Initially, the experiment was started with two different sediment materials. One coarse material for the existing river bed, and a finer distribution for the new river bed in the expansion section.

The new topography has been tested by representing several flood events (maximum 450 m³/s corresponding to a 100 year flood) in the physical model. After each experiment the bed topography has been determined using automatic controlled and positioned laser distance meters. It could be shown that pronounced scouring takes place at several positions, for example at the end of the widening section, where increased flow velocities can be observed. To avoid these scouring phenomena close to the banks, the VAW is currently optimizing a solution using groyne fields in the expansion.