Hydrodynamics of the Orne and sediment mobilization in the backwater zone upstream of the Beth dam (Lorraine, France)

摘要

Orne suffered multiple hydro-morphological changes in the XX th century, in relation to the steel industry located in the downstream valley. In Moyeuvre-Grande, the Beth dam, built in 1958, causes in particular a backwater zone 4.5 km in length, locally presenting alluvial banks as well as solid deposits heavily contaminated by past industrial activity. A study in progress aims to determine the remobilization of these polluted deposits under current hydrological conditions and with a view to removing the dam. This work specifically studies the hydrodynamics of the Orne in the slowdown zone caused by the dam. The biennial flood of the lit June 2016 is used as the benchmark event; its maximum flow at 137 m(3) / s corresponds locally to the flow at full edges. The morphometric study of two sites with a sedimentary bank spaced 450 in apart made it possible to calculate the specific power and the traction stress of the watercourse, coupled with grantdometric measurements. The specific power (about 30 W / m(2)) and the average traction stresses (between 15 and 22 N / m(2)) show the relatively low hydrodynamic energy of the watercourse which can however mobilize sediments of centimeter size by bedload and sand medium to coarse in suspension, during a biennial flood. These first results will be used for the hydraulic modeling which will be done near the dam in order to determine the ablation processes that could occur there following the opening of the valves,