Reduction of sediment deposition by introducing an artificial stony bank. A practical example in upper Rhone river, Switzerland

摘要

The flood occurred the 10 October 2000 in the Dranse river, a tributary of the Rhone river, near Martigny, Switzerland, generated an important raise, about 80 cm, of the natural bed in a bend located 150m downstream from a bridge (Bathiaz bridge). The bed raise, due to a massive sediment deposition event, led to a dangerous diminution of the river hydraulic capacity. For this reason, Bonnard & Gardel consulting engineers, was charged by the Martigny municipality to study the Dranse stretch affected by the sediment deposition and to propose a hydraulic rehabilitation to optimise the flow and minimise future bed raises. First, the river stretch was investigated by using a quasi-2D numerical model (GSTARS 2.0) to simulate the flood event. The model was used to analyse and evaluate several possible solutions. The model showed that a rip-rap reinforcement of the external part of the bend associated with the creation of an artificia stony bank at the internal part of the bed led to a significant reduction of the sediment deposition in case oi' flood. This result is due to the flow acceleration induced by the internal bank associated to the reduction of the local erosion obtained with the external reinforcement. A physical model realised at the Polytechnic School of Lausanne (EPFL) validated the solution proposed. The paper describes the results obtained by using the numerical and physical model under the hydraulic and feasibility point of view.