Optimisation de l'efficacité des ouvrages d'hydraulique douce pour réduire les coulées d'eau boueuse en Alsace : Une étude de modélisation par le modèle openLISEM

Abstract

Water erosion causes a lot of damage every year in villages and in agricultural plots. The consequences of this phenomenon are muddy flows. In the Alsace, this phenomenon tends to increase, in particular in the Kochersberg and Sundgau regions. This intensification is linked to heavy storms, spring crops, sensitive loamy soils, and a pronounced relief. In order to combat these events, vegetative barriers (fascine, grass strips, miscanthus strips and hedges) can be installed in the catchment. So far, size and position of these barriers in the landscape are often decided on the basis of practical considerations; a decisional framework helping to maximise the reduction of fluxes the catchment outlet by considering the optimal type, location, spatial density and dimensions of such barriers in the catchment is still missing. The goal of this work is to provide guides for the choice of the position and number of barriers in the catchment and to adapt the barrier type to the type of the incoming flow (non-concentrated or concentrated). In order to optimise the reduction of water and sediment output at the outlet of catchements. This work is carried out by simulations using the openLISEM software on two watersheds, one in Eckwersheim (67) and one in Ruederbach (68). Modelling results show that some structures have greater efficiency in reducing soil losses, such as hedges, fascines and miscanthus strips for non-concentrated flow. For concentrated flows, hedges and fascines are effective. In order to reduce peak discharge, the miscanthus strips and hedges are suitable structures for non-concentrated flow, while for concentrated flows only fascine and miscanthus strips are suitable. In addition, these structures must be at least 10 meters wide for the miscanthus strips, and hedges must be composed of 6 rows. This study also highlights the role of joint cropping plans, reduced tillage and the management of grassed areas and ditches. These measures must be completed by the implementation of vegetative engineering works to reduce the problem of muddy flows.