Abstract: Dike-break flooding is a main natural disaster that could cause losses in life and property on river floodplain, and studying its routing characteristics is crucial to protection of such areas. However, complex types of the underlying surface of a river floodplain produce different flow resistances. In this study, a generalized physical model and numerical simulations are used to examine the influence of buildings distributions on flood routing over the Lankao-Dongming floodplain area of the lower Yellow, focusing on the flows over an area of buildings arranged in four different patterns under four main channel discharges and four incoming flow angles. The experimental results show that flow depth over this area is increased with the increase in the inflow discharge of the main channel and its flow resistance varies with different building arrangements. Then, we use a two dimensional hydrodynamic model to calculate the flood inundating process, and obtain calculated flow depths in good agreement with the measurements. For the building area, different Manning coefficients are calculated for the simulations to improve its resistance modeling by comparing to the corresponding measured depths. Results show that at Manning coefficients of 0.05, 0.08, 0.12 and 0.16, the calculated depths are in good agreement with the measured values under building patterns of 3×3, 4×4 and 5×5 arrays and a staggered array respectively; and that the location of the simulated hydraulic jump are nearly the same as experimentally measured. This study helps the planning of building arrangement on river floodplain to reduce dike-break flooding, and it is also useful for verifying the accuracy of hydrodynamic models.

Key words: floodplain floods, physical experiment, numerical modelling, building distribution, resistance coefficient