[T8144]砂防学会誌63‐1/P31‐38 報文

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1 VolNop Outbreak process of debris flow occurred at the Kitamata Valley of Name River on June 27, 1999 Akihiko IKEDA Jun ichiro TAKAHAMA Kousuke YOSHINO Abstract To estimate debris flow peak discharge and hydrograph are important for effective disaster prevention. Ikeda et al. (2007) has presented occurrence criteria of debris flow must be evaluated not only rainfall condition but also supply process of materials. At the Kitamata Valley of Name River, three debris flows occurred in 1999 as the result of landslide dam that blocked the riverbed near an elevation 1800 m in The largest debris flow of these was occurred on June 27, forming a conspicuous peak with relatively high velocity. Analyzing the occurrence situation and flow property of this debris flow by field research, aerial photograph interpretation, and CCTV camera figures, we estimate the outbreak process and hydrograph of this debris flow. Using the two layer sediment transport model Takahama et al. (2000) have developed, shape of hydrograph and peak discharge was well explained with the exception of total volume and a duration of debris flow. Also the hydrograph shows that the supply process of materials will be an outburst of a landslide dam. Moreover, comparison the peak discharge and hydrograph between the case with landslide dam and without it, the peak discharge is larger than without landslide dam, also the total volume of debris flow. Key wordsdebris flow, outbreak process, supply of material, landslide dam, Kitamata Valley m Ikeda and Hara interface Member, Sabo Techincal Centerikeda@stc.or.jp Member, Graduate School of Life and Environmental Science, Kyoto Prefectural University Member, Incorporated Administrative Agency, Public Works Research Institute

砂防学会誌 Vol ６３ No １２８８ May ２１動的に起動する仕組みになっている CCTV カメラは北２滑川北股沢と土石流観測システムの概要股沢第４号堰堤を正面から撮影するカメラ No １同堰堤直下流の渓床を真上から撮影するカメラ No ２北股滑川北股沢は木曽駒ヶ岳標高２５６m を源流とす２る流域面積６２km 流路延長５２km 平均河床勾配１

2 砂防学会誌 Vol ６３ No １２８８ May ２１動的に起動する仕組みになっている CCTV カメラは北２滑川北股沢と土石流観測システムの概要股沢第４号堰堤を正面から撮影するカメラ No １同堰堤直下流の渓床を真上から撮影するカメラ No ２北股滑川北股沢は木曽駒ヶ岳標高２５６m を源流とす２る流域面積６２km 流路延長５２km 平均河床勾配１沢第１号堰堤２号堰堤間の河道を右岸渓岸から撮影す３２の急勾配荒廃渓流である図１図２流域のるカメラ No ３と滑川第一砂防ダムの堆砂域を撮影する基盤地質は脆弱な花崗岩類でありかつ高標高地であるカメラ No ４の合計４基が設置されているなおこれために凍結融解作用による荒廃が著しく非火山地域でらのカメラには投光器とワイパーが併設されているまありながら過去から現在に至って頻繁に土石流が発生した流域内には１箇所の雨量計が設置されているている特に１年には６月から月までの３カ月の３１年６月２７日土石流の発生流下状況間に３回の土石流が発生した６月２７日月１５日月２４日１年６月２７日土石流発生前の１８年１１月２日と滑川北股沢における土石流観測施設の設置状況を図発生後の１年６月２８日月日月１７日に撮影３に示す本システムは滑川第一砂防ダムの上流５５ m された空中写真の比較判読と現地調査に基づく土石流の１３ m に位置する治山堰堤群と河道に設置された２２発生状況ならびに CCTV カメラの VTR 画像の分析に本のワイヤーセンサーが土石流の通過によって順次切断基づく土石流の流下状況は以下のように推定されるされセンサー切断の検知とともに CCTV カメラが自３１土石流の発生実態空中写真の比較判読の結果１年６月２７日の土石流の発生源は上流域右支渓の標高２３ m 付近の土砂堆積地とその下流の標高２１２３ m 付近の河道図１滑川北股沢流域の位置図 Fig １ Location of the KitamataValley 図２滑川北股沢流域の縦断図 Fig ２ Longitudinal profile of the KitamataValley 図３土石流観測地点土石流発生源天然ダムの位置図 Fig ３ Location of the observation system, source of debris flow and the landslide dam ３２

3 m mkm m m m AI I m m m A No VTR No VTR No NoNo No No NoNo NoNo n n Ikeda and Hara n n n msms msms m mm m sm Changes in the mean velocity, flow depth, discharge of debris flow

4 Vol NoMay hw t B hs t B cshs t B zb t st B cosθ Mw t vw Bhw si x vs Bhs stsi x csvs Bhs c*st x vw Mw x siui B ghw sinθ ghw cosθhw ghw cosθhs x x τ w ρ w Ms vs Ms t x ρ s st ρ w ρ s ρ ssivs ρ w ρ s ghs sinθ ρ w ghs cosθhw ρ s x ghs cosθhs s ghs cosθρ x ρ s x τ wτ b ρ s sw Mwvw BhwMsvs Bhs h v cs siui cst si interface θ zb ρ ui interface x g τ w interface τ b τ bτ yρ w fsvsvs τ ycs σ ρ wcs ghs cosθ tanφ s c τ extzzbτ ykzzb Gyk ρ w ghs σ ρ wcsθ σ ρ wcs θcs φ s c Gyk fs fcsgyk W GykW W GykW Gykhs Gyk d fsfcshs d interface τ w W ρ w ghs fwvwuivwui ghs fw κ η hwln hw ηkfcs cs d η stvtanθ θ e σ ρ wc tanθ e tanφ s σ ρ wcρ w σ C v

5 θ e φ s kfkge κ d τ extzzbτ ykzzb c ρ w ρ w σ cfρc cl a m m m b m m c cfc clc c xm cfccσ gcm ρ gcm ρ wgcm φ d cm c VTR mm km m s d m m e m Δ xm Δ ts Longitudinal profile and flow width Longitudinal profile of landslide dam

6 Vol NoMay Longitudinal changes in calculated results of accumulated and yielded sediment volumescross section Longitudinal changes in calculated results of accumulated and yielded sediment volumescross section at series of check dams Hydrograph around the landslide dam Hydrograph between the section of Check Dam No. 4 and No. 11

7 Flow depth around the landslide dam Flow depth between the section of Check Dam No. 4 and No. 11 xm m sm xm m sm x m m s m m s VTR m s m m VTR

8 Vol NoMay Comparisons of calculated results of changes in the velocity, flow depth, discharge and analyzing data Vol Nop VolNo p Ikeda, A., Hara, Y. (2002) : Debris flow generated at Kitamata Valley of the Name River. International Congress INTERPRAEVENT 2002 in the Pacific Rim-MATSUMOTO / JAPAN : Congress publication, vol. 1, p Ikeda, A., Hara, Y. (2003) : Flow properties of debris flows on the Kitamata Valley of the Name River, Japan. Debris-Flow Hazards Mitigation : Mechanics, Prediction, and Assessment, Rickenmann & Chen (eds), p p p p p p p

mm mm , ,000 Fig. 1 Locality map of the investigation area NE SW Fi

mm mm , ,000 Fig. 1 Locality map of the investigation area NE SW Fi 5 Report on the Landslide Disaster in the Upper Part of the Abukuma River, Fukushima Prefecture, Due to Heavy Rainfall in August 1998 By Takashi INOKUCHI National Research Institute for Earth Science and