Main channel width effects on overtopping-induced non-cohesive fluvial dike breaching

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Laboratory experiments were conducted on the breaching of homogeneous non-cohesive sandy fluvial dikes induced by flow overtopping. Tests were conducted using a main channel, an erodible lateral dike and a floodplain. The main channel width and Froude number prior to overtopping were systematically varied. Breach discharge was deduced from water level measurements and mass conservation. High-resolution 3D reconstructions of the evolving breach geometry were obtained using a non-intrusive laser profilometry technique. The main channel width and Froude number show significant influence on the breach expansion and hydrograph. Breach hydrographs are divided into three types, depending on the Froude number and a non-dimensional main channel width. An adapted fluvial dike breaching model based on the concept of “effective breach width” is proposed. Using the laboratory data, the computed breach discharge is found extremely satisfactory, although the breach downstream expansion is not accurately reproduced by the model.