Experimental studies on farm dike-break induced overbank floods using a sketched physical model

Farm dikes constructed along the main channel in the Lower Yellow River can withstand small and median floods, and protect farmland and villages from flooding. Farm dike-break induced overbank floods not only cause water level changes in the main channel, but also lead to severe flood disasters on the floodplain. Numerical simulation is often employed to study dike-break floods, and previous results obtained from prototype and model measurements are very limited. In this study a sketched laboratory model was constructed to investigate the inundation process of farm dike-break induced overbank floods, and characteristics of water level changes along the main channel and over the floodplain were analyzed. Experiment results show that:① after the farm dike burst, the diffusion flood wave rapidly routed over the floodplain, which caused the surface-negative wave in the main channel and the surface-positive wave on the floodplain. Water levels in the main channel decreased first, and then kept stable, and then rose to another stable level, and the rates of water level change were different in the reaches upstream and downstream of the dike breach site. Water levels on the floodplain generally kept rising firstly and finally tended to be stable, with inverted slopes of water surface in local regions; ② arrival times of wavefront routing in overbank floods were mainly associated with the terrain and the distance from the site of dike breach, and the measured wavefront had a distribution of symmetric elliptic shape firstly and then a asymmetric distribution. Hydraulic jumps occurred in the process of dike-break induced overbank floods, and the position of hydraulic jump gradually approached the dike breach site from a farther distance; and ③ the breached discharge was directly related to the difference in water levels on both sides of breach. The breached discharge decreased first, and then remained stable, finally decreased to zero. Experimental results can provide the basis experimental data not only for the research into overbank floods due to farm dike-break, but also for validation of mathematical models.