The floodplain domain is a base of living and development of local communities in the Lower Yellow River (LYR), and it is also an important site for flood routing, flood retention, and sediment deposition. The farm dikes constructed along the main channel in the LYR can withstand small and median floods, and protect farmland and villages from flooding. However, when a great flood occurs, it is very easy to cause farm dike to breach, and the dike-break induced floods usually cause catastrophic loss of human life and property. In this study, a laboratory model was constructed to study the routing of farm dike-break induced floods, and the characteristics of water level variation in the main channel as well as the propagation process of flood wave on the floodplain were analyzed based on the measured data. A two-dimensional numerical model based on the finite volume method with unstructured triangular mesh was then employed to study dike-break floods, and the model was then validated by the measurements, and close agreement was obtained between the model predictions and the experimental data. Finally, the validated model was used to simulate the dike-break floods using different roughness values in floodplain area, and the effects of floodplain roughness on water level, flow velocity and arrival times of wavefront routing were investigated. The results show that:1) after the farm dike breached, water levels in the main channel decreased first, and then kept stable, and then rose to another stable level, and water levels on the floodplain generally kept rising firstly and finally tended to be stable. The flow velocities on the floodplain generally kept increasing firstly and then decreased to zero. The breach discharge decreased first, and then kept stable, and then decreased to zero; and 2) the floodplain roughness degrees have no significant effects on the breach discharge and overbank flood routing, but have a great influence on the arrival times of wavefront routing. The arrival times of wavefront routing on the floodplain increased gradually with an increase in floodplain roughness degrees, which decreased gradually with an increase in inflow discharge. The flow velocity on the floodplain decreased gradually with an increase in floodplain roughness degrees.The results could deepen the understanding of dike-break floods routing, and be applied as reference for the subsequent relevant researches.
