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 flowmoved 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.

Development and installation of bedload monitoring systems with submerged load cells

Bedload governs riverbed channel variations and morphology,it is necessary to determine bedload discharge through an arbitrary cross section in a mountain river.A new system with submerged load cells has been developed to directly measure bedload discharge.The system consists of:(1)an iron box which is 1 m long,0.5 m wide and 0.1 m in depth,(2) two submerged load cells 0.7 m apart,(3) a pressure sensor and,(4) an electromagnetic velocity meter.This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements of bedload particle weight.Initial tests in a laboratory were conducted to examine the accuracy of measurements with the system under aerial conditions.The system has been installed in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute(DPRI) of KyotoUniversity to obtain bedload discharge under natural conditions.Flume tests were conducted in this channel by artificial supply of uniform sediment particles of several grain sizes.The average velocity of the sediment particles near the bed was estimated using cross-correlation functions for weight waves obtained by the two load cells.Bedload discharge calculations were based on time integration of the product of sediment velocity and sediment weight obtained by the two load cells.This study clarifies the reasons why bedload measurements are difficult,and provides some solutions using the monitoring systems with submerged load cells through the field measurements.Additionally,the applicability of bedload measurement with the submerged load cells is explained based on experimental artificial sediment supply data.