Yoshifumi Satofuka

Influence of housing and urban development on debris flow flooding and deposition

Debris flows form deposits when they reach an alluvial fan until they eventually stop. However, houses located in the alluvial fan might affect the debris flow flooding and deposition processes. Few previous studies have considered the effects of houses on debris flow flooding and deposition. This study conducted model experiments and numerical simulations using the Kanako2D debris flow simulator to determine the influence of houses on debris flow flooding and deposition. The model experiments showed that when houses are present, the debris flow spreads widely in the cross direction immediately upstream of the houses, especially when the flow discharge is large or the grain size is small. Houses located in the alluvial fan also influence the deposition area. The presence of houses led to flooding and deposition damage in some places and reduced the damage in others. The simulation also demonstrated the influence of houses. Both the model experiment and the simulation showed that houses change the flooding and deposition areas.

Case study of debris flow disaster scenario caused by torrential rain on Kiyomizu-dera, Kyoto, Japan - using Hyper KANAKO system

This paper presents debris-flow numerical simulations using the Hyper KANAKO system, developed by the authors. The system uses the debris flow simulator KANAKO 2D equipped with a graphical user interface (GUI); hence, a user can easily produce appropriate landform data for simulations using standard laser profiler data, and visualize the results using a GIS. Hyper KANAKO was applied to the streams around Kiyomizu-dera in Kyoto, Japan. Kiyomizu-dera is a famous temple in Japan which is visited by numerous tourists throughout the year. We simulated a disaster scenario of debris flow caused by torrential rain. We set the hydrograph using rainfall intensity data, and set the landform data using information from the Geospatial Information Authority of Japan (GSI) and a digital elevation model (DEM). We evaluated different mesh sizes and also used a digital surface model (DSM) to consider the building heights. The simulation results showed that with small mesh size, the debris flow moved through the roads, which seems realistic for a disaster situation. When buildings were considered, the flow direction changed, and a 1-m flow depth, which was deeper than in other cases, appeared in the flow path. This may pose a dangerous situation for evacuations.