Effects of upstream and downstream slopes and clay content on levee's breaching by overtopping

The present study investigated the effects of clay content and levee's slopes on the breach formation process for levees constructed by both cohesive and non-cohesive soils. Twelve experiments were carried out and the breach formation of levees was observed by measuring the breach discharge variations and scour topography with time. The initiation of surface erosion was analysed by comparing the estimated bed shear stress and the critical soil shear stress, and the rate of erosion during breaching was estimated by employing the erosion index. The erosion of levees due to overtopping was classified into three regimes of uniform surface erosion, erosion from the toe, and single scour formation. It was found that the upstream levee's slope had negligible effects on the breach process, whereas the downstream slope significantly increased the erosion index. The peak breach discharge increased with increasing downstream slope and it occurred earlier. Experimental results also showed that the peak breach discharge was higher in non-cohesive levees than the cohesive embankments and it occurred much earlier. Based on dimensional analysis, empirical equations were proposed to predict the breach discharge and the topography of erosion during the breach.