At the end of 2019, we constructed two artificial sills on the Avançon d’Anzeinde river for our client Romande Energie SA in order to remove barriers hemming in migratory trout. We were able to apply our experience in the renaturation of bodies of water.
The two sills we worked on were set at a distance of 40 metres from each other, not far from the hamlet of Pars, in the municipality of Gryon. The existing sills were made from railway sleepers measuring approximately 5 metres wide, with a drop height of 1.6 m and 0.4 m.
The solution we put forward to our client involved replacing each passage with a riprap ramp. To guarantee the trout could pass over the ramps, the structure was designed to guarantee a minimum water level of 20 cm and limited maximum drop of 20 cm. A bypass channel was also incorporated in each ramp in order to maintain these conditions even during low-flow conditions.
After having removed the existing sleepers, we proceeded to install the two ramps, one 25 m in length and the other 9.5 m. The new sills (11 for the big ramp and 3 for the small one) stabilised the ramps. We then positioned stone blocks between the sills, providing the fish with somewhere to hide and rest.
Our client Romande Energie SA was very pleased with our work, which was completed over a period of 4 weeks at the end of 2019 while the water level of the Avançon d’Anzeinde was low and there was minimal risk of flooding.