Restoration of an alluvial mattress using artificial armour layer Experimental study on the river Ouvèze (France)

摘要

Sogreah has been commissioned by the Syndicat Ouvèze Vive to perform a comprehensive study of solid transport andrnmorphodynamics for the river Ouvèze (Ardèche, France)rnThe river Ouvèze (catchment area = 123.5 km²) is a right-bank tributary of the river Rhone that is subject to typicalrnCévennes area rainfall. Most of its bed currently consists of outcropping substratum over almost its entire length. Thisrnriver was subject to very little natural bed movement, with a relatively high level of solid transport (estimated atrn4,000 m3/year at the confluence with the river Rhone), but a rather thin alluvial mattress (probably around 1 to 2 m).rnThe volume of alluvial materials extracted over the past forty years is estimated to be comparable to a century ofrnnatural transit: a generalised incision of the bed has occurred, leading to the disappearance of the alluvial mattress,rnthereby exposing a fragile substratum.rnThis bed incision raises problems, not so much because of the deepening of the riverbed but rather because of thernexposure of the substratum. Indeed, the river currently flows over large marly-chalk slabs, leading to negativernenvironmental impacts and, in particular, the destruction of fish habitats and the loss of attractive river features. Thernaim is therefore to restore an alluvial mattress.rnThe traditional method used to restore an alluvial mattress is to build sills across the river bed. This method has arnnumber of drawbacks: in particular, it blocks alluvium, thus creating a shortage downstream of the sill, so this solutionrnwas not selected for this project.rnSogreah proposes an innovative, experimental technique: the restoration of an alluvial mattress using artificial armourrnlayer. This technique consists in covering the riverbed with coarse alluvium, which resists the tear-out force of the flow.rnThe dimensions of the materials brought in must therefore be sufficient for this purpose.rnThe plan is to try various solutions and materials on several pilot sites before generalising the protection process to thernentire length of the river affected.