It is important to prepare sets of detailed and accurate experimental data obtained in a large-scale channel to develop a reliable numerical model for inundation flows. This study makes a detailed measurement of temporal and spatial variation of water depth for overland flows caused by the break of channel dyke. A two-dimensional numerical model is also proposed employing CIP-CSL2 method to directly capture the variations of flow and complex geometry within a computational cell. The comparison between the experimental data and the numerical results reveals that the present numerical model can reproduce the characteristics of inundation flows under steady and unsteady conditions and with and without buildings.