ESTIMATION OF LEVEE FAILURE POINTS BASED ON LEVEE VULNERABILITY INDEX AND FLOOD RISK ANALYSIS BY INTEGRATING SIMULATION OF FLOOD FLOW AND INUNDATION

ABSTRACT To examine the flood risk management measures, it is important to estimate the levee breach points, inundation discharge hydrograph and motion of the inundation water in the basin as precisely as possible. The purpose of this paper is to conduct the above series of studies on the Kinu River (Japan) suffered from inundation in the range of 40 km2 due to overflowing and levee breach during the 2015 large flood. First, a simulation model integrating flood flow and inundation is developed. The inundation discharge hydrographs due to the overflowing and levee breach are estimated by the flood flow analysis based on observed temporal changes in water surface profiles in the Kinu River. The inundation is calculated by a two-dimensional model. The mesh of the inundation analysis model is generated by regular grid with 5 m size in order to express the microtopography obtained by DSM (Digital Surface Model). Manning’s roughness coefficients are given according to the situation of the land use and inundation depth. It is confirmed that the developed model is useful by the inundation arrival time read from camera images and the spread of the actual inundation water in the basin. Next, the suitability of the levee vulnerability index t* which has been derived by the authors is examined for the levees of the Kinu River. Finally, the inundation flow analysis is conducted under the actual and hypothetical levee breach conditions based on the value of t*. It is concluded that the difference in the location and time of the levee breach influences on the motion of the inundation water and inundation areas in the Kinu River basin.