Large-scale experiment on dike breaching with complex measures on the crown

Dike breaching is the main component of flood defending system. To temporally enhance the capacity of the river, small levees will be build on the dike crown to increase the elevation of the dike crest. Also, the dike top usually be paved with concrete as transportation road. Under these two condition, break mechanism are different from those without complex measures on the crown, which has not been investigated yet. Large-scale experiment has been carried to investigate the breaching mechanism. Results show that with small levees, the flow forms a little fall at the downstream edge of the levee top and a much larger fall on the downstream face of the dike. The “headcut” backward retreat is the main breaching mechanism in the early stage of breaching. During the rapid development stage of breaching, the vertical erosion, lateral erosion and gravity collapse are the breaching mechanism. The existence of the external small levee protected the top of the dike from erosion for a long time, which largely delayed the breaching processes. As the top was paved, the breaching processes likes that of dike with small levees. Two falls forms at the edge of the road and at the downstream face respectively. When the backward retreat of “headcut” at the downstream face of the dike reaches the base of the dike, the underneath soil is washed away and lead to concrete of the road collapse. Once the road is collapsed completely, two falls merged into one, thereafter the breaching processes likes dikes without complex measures on the crown. The paved road also delayed the breaching processes. This study can provide scientific support to dike breaching emergency management.