Hazard mitigation planning for debris flow based on numerical simulation using Kanako simulator

Abstract

Debris flow often causes enormous loss to life and property, especially on alluvial fans. Engineering structures such as retention check dams are essential to reduce the damage. In hazard mitigation evaluation and planning it is of significance to determine the location, size and type of dam and the effects of damage mitigation. We present a numerical simulation method using Kanako simulator for hazard mitigation planning of debris flow disaster in Tanjutani Gully, Kyoto City, Japan. The simulations were carried out for three situations: 1) the simulations of erosion, deposition, hydrograph changing and inundation when there were no mitigation measures; 2) the simulations of check dams in four locations (470 m, 810 m, 1,210 m and 1,610 m from the upstream end) to identify the best location; 3) the simulations of check dams of three types (closed, slit and grid) to analyze their effects on sediment trapping and discharge reduction. Based on the simulations, it was concluded that two closed check dams (located at 470 m and 1,610 m from the upstream end) in the channel and a drainage channel on the alluvial fan can reduce the risk on the alluvial fan to an acceptable level.