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適当な大きさの固体粒子を容器内に充填してその底から均一に空気を吹き込むと、粒子はある高さまで浮遊して激しく動き回る状態になる。この激しく動き回る粒子の層を流動層といい、流動層を発現させる装置を流動床という。流動床は燃焼ボイラー、ゴミ焼却炉、水処理プラント、化学反応槽、乾燥装置などさまざまな目的で工業的に利用されている。流動層と本質的に同様の現象は、自然界においても数多く認められる。例えば、火山灰が高温の火山ガスの噴出とともに流動化して高速で移動する火砕流、地震動により未固結の砂層を構成する粒子相互の噛み合いがはずれて地下水中に砂が浮遊する状態となり流動化する液状化現象、豪雨時に崩壊した斜面から供給された多量の土砂と渓流水とが混合攪拌されながら流動性が急激に上昇して高速で沢を流下する土石流などである。こうした自然現象の再現や検討に際して流動床を活用することは、基本的な機構が共通するので現象の理解の促進に有益と考えられる。しかし、地学教育分野で流動床を活用した教具や教育事例は知られていない。そこで本研究では、簡単・安価に作成でき、運搬や運転が容易で、学校を始めとする教育現場で活用容易な流動床発生装置の作成方法を検討し、適当な装置の緒元を紹介することを目的とした。市販の樹脂製小型水槽、塩化ビニールパイプ、左官用珪砂、家庭用排水ホース、ヘアドライヤー等を組合せて作成できる簡易な流動床発生装置の概要を紹介するとともに、地学教育への適用可能性について述べる。

：The archaeological excavation method supports the applied Geomorphological map making for disaster prevention as the details of geomorphological history and processes in lowland and hills during the last some 1,000 years are not always known. The current Flood Hazard Maps in Japan come to show the simulation of high risk area in the case of the supposed extreme rainfall that is the 1-in- about 1000 years rainfall. To prove the existence or no-existence of 1 in 1000 years flood, only the archaeological method is effective now. In the flexible soil mapping based on boring and geomorphic reading, the knowledge of the micro-relief at some time in the past which archaeological survey excavated is helpful. Diagnosis of stability and un-stability of landslide slope and its movement history are also known in some excavated archaeological sites.

令和元年（2019 年）東日本台風によって宮城県丸森町周辺と岩手県三陸海岸沿いでは，多数の斜面変動（斜面崩壊や土石流）が発生した．土砂移動分布図の作成や現地調査により，斜面変動の分布を調査し，それらと雨量・地質との比較を行った．斜面変動は，火山岩類や付加体などの堆積岩類の分布域と比べて，花崗岩類の分布域に多く発生した．花崗岩類の分布域では，概ね6 時間雨量と24 時間雨量がそれぞれ約180 mm，約300 mm を超えると斜面変動が増え始め，特に，6 時間雨量が約250 mm かつ24時間雨量が約400 mm を超える場所では斜面変動が密集する傾向がある．斜面変動の発生頻度や個々の斜面変動の規模・流出土砂量は，各地域の雨量差を反映して，丸森町付近が最も大きく，次いで重茂・船越半島が大きくて，普代村はそれより小さいと考えられる．Serious slope disasters were induced by Typhoon Hagibis on October 2019 near Marumori Town, Miyagi Prefecture and Sanriku coastal area, Iwate Prefecture. The distribution of slope movement (e.g. slope failure, debris flow) was investigated by developing a trace map of sediment movements by air photo interpretation and field survey, and the rainfall distribution and geology were compared. Slope movements occurred more frequently in the area of granites than in the areas of volcanic rocks and sedimentary rocks such as accretionary prisms. In the area of granites, slope movements began to increase when the 6-hour rainfall and the 24-hour rainfall exceed about 180 mm and 300 mm, respectively. The slope movements concentrated in slopes where 6-hour rainfall exceeds 250 mm and 24- hour rainfall exceeds 400 mm. The occurrence frequency, size and amount of sediments of slope movements were the largest near Marumori Town, followed by the Omoe and Funakoshi Peninsulas, and smaller in Fudai Village, reflecting the differences in rainfall in each region.

Eruption with Vulcanian type continued at the summit craters Minamidake and Showa continued since 1955. Volcanic disaster during the eruptive period is summarized. Factors causing disasters are volcanic block, lapilli, ash, air-shock, and debris flow triggered by rain fall. No disaster was induced by pyroclastic flows. Volcanic blocks ejected by 20 explosions reached distances >2.5 km and destroy residential houses and hotels. Lapilli fall broke windows of cars, and such a disaster occurred up to a distance of 20 km (87 events). Air-shocks (>300 Pa) broke windows of houses and buildings (39 events). Debris flow triggered by rain fall frequently occurred after a large amount of volcanic ash deposition.

紀伊半島の白亜系付加体である日高川層群の分布域で，平成23年の台風12号によって発生した斜面崩壊と土石流の特性を分析した．日高川層群は，沈み込む海洋プレートによって付加体深部に押し込まれたため，破壊により細片化した岩石からなるので，風化によって最終的には細粒物質を中心とする厚い風化層ができる．しかし，地下深くの高圧で強く再固結した岩石でもあるので，風化・侵食に強く高い山を形成しており，山腹斜面の河床からの比高は四万十帯の中で最も大きい．山腹斜面に生成された細粒の風化物質は，山腹斜面の全面で一斉に崩壊を起こす場合と，分割して崩壊する場合とがある．前者の場合は，先行河川である緩傾斜の本流の河床に崩落することが多く，その場所に厚く堆積して天然ダムを形成することも多い．後者の場合は，山地の隆起ととともに形成された急傾斜の渓流に崩落することが多く，土石流に転化して渓流沿いに長距離流下する．他の地質帯と異なり，このような２つのタイプの斜面崩壊/土石流が発生する日高川層群地帯では，これらを認識できるような防災教育が必要で，そのための地域住民向けの教育素材も考案した．, I analyzed the characteristics of slope failures and debris flows caused by typhoon No. 12 in 2011 in the distribution zone of the Hidakagawa Group, which is a Cretaceous accretionary prism on the Kii Peninsula. Since the Hidaka River Group is pushed into the deep accretionary prism by the subducting oceanic plate, it is composed of rocks that have been fragmented by fracture, weathering eventually results in a thick weathered layer centered on finegrained material. However, since it is also a rock that has been strongly reconsolidated at high pressure deep underground, it forms a high mountain that is resistant to weathering and erosion, and the relative height from the riverbed on the hillside slope is the highest in the Shimanto geologic belt. The fine-grained weathered material generated on the hillside slope may collapse all at once on the entire surface of the hillside slope, or it may collapse separately. In the former case, it often collapses on the riverbed of the gently sloping mainstream, which is the preceding river, and often accumulates thickly at that location to form a landslide dam. In the former case, it often collapses on the riverbed of the gently sloping mainstream, which is the preceding river, and often accumulates thickly at that location to form a landslide dam. In the latter case, it often collapses into a steep mountain stream formed with the uplift of the mountains, and it is converted into a debris flow and flows down a long distance along the mountain stream. Unlike other geological zones, in the Hidaka River Group where these two types of slope failures / debris flows occur, disaster prevention education that can recognize these is necessary, and educational materials for residents have been devised for that purpose.

沖縄島南部に位置する運玉森の周辺には｢与那の島の惨事｣という災害伝承がある。その南東麓にある久葉堂という拝所は、この伝承と関連する可能性が指摘されている。しかしそれを裏付ける文書等の資料を見出せず歴史学的検証は困難なことから、微地形分類および各種地図情報の判読等の地理学的手法により、伝承の実態把握を試みた。その結果、｢与那の島の惨事｣とは、近世後半に起きた土石流災害によって、久葉堂周辺すなわち現在の与那原町与原付近にあった村落が壊滅した事象であると比定した。また地名の解釈から、壊滅した村落は現在の与那原町の中心である新島に移転して再興された可能性が高い。すなわち与那の島は与那原の原型あるいは前身といえる村落であった。20 世紀初頭の旧版地形図では久葉堂・与原付近に人家は無く、純然たる拝所・被災地として保全されていたように見受けられる。しかしながら、一般にこうした大規模土砂災害の発生頻度は低く、再来間隔は人間の寿命や世代交代のスパンを大きく上まわる。また対象地域は戦時中に要塞化され、さらに激戦地となったことも重なり、伝承の災害知は題目だけを残して忘れられてしまった。久葉堂も、戦後、新たにできた与原集落の拝所となったがゆえに、その由来や存在意義が曖昧になってしまった。一方で、沖縄県の行政レベルでは、与原付近の土砂災害リスクが明確に把握されている。このような環境下での住民の地域認識や現実的な防災意識を涵養するため、整備が進むハザードマップの周知と共に、｢与那の島の惨事と久葉堂の由来｣のような、地域固有の災害知の発掘と共有が望まれる。, There is a folk legend that "Yona no shima" (Yona village) was destructed by a natural disaster occurred around Untama-mui (Conical hill), southern part of Okinawa island. This report reveals the legend through geographical approaches. Analysis of micro geomorphology in the study area shows that the disaster was a large debris flow occurred in the period from late 18th Century to early 19th Century. The debris flow destroyed a village located in Yohbaru area. Survivors of the disaster restored a new village in Mijima area, which was located about 1km south of Yohbaru. Mijima is the present town center of Yonabaru. Yohbaru area had been conserved as a disaster memorial sanctuary until early 20th Century. Kufa-do shrine, a place of worship in Yohbaru, was constructed as a symbol the sanctuary. In the present, however, the legend has been almost forgotten due to Battle of Okinawa and subsequent development. Yohbaru area has been developed as a "new town" despite of its disaster risk. Similar settlements are widely distributed in Okinawa island. We must remember the disaster knowledge of predecessor.

Field observation and numerical analysis were performed for the debris flows which were occurred in Koyasu, Marumori, Miyagi in Oct, 2019 and in Kinryu, Saga in Aug, 2019. Three debris flows were happened in Koyasu area and those debris flows destroyed a house completely. The results of the numerical analysis show that the debris flow approached at the residential area in 40 sec. and it is very difficult to evacuate after the occurrence of debris flow. On the other hand, the debris flow approached at the residential area in 600 sec. in Kinryu, because development of debris flow was slow. People, therefore have enough time to evacuate after the occurrence of debris flow.

Article, 環境科学年報 42:24-29(2020)

Field observation and numerical analysis were performed for the debris flow which was hap-pened in Kumano, Hiroshima in July, 2018. Three debris flows were happened and the debris flow from the north valley attacked the residential area and damaged many houses. The debris flow com-poses of wide graded sediment. The results of the numerical analysis show that the debris flow approached at the residential area in 50 sec. and the average speed on the slope is 9m/s. The information of the inundation area and the debris flow depth can be used to consider the evacuation method in case which people cannot evacuate in long distance during the heavy rain.

我が国では梅雨や台風時に土砂災害が多発しており，土砂災害の中でも人的・物的被害が大きくなるものとして土石流がある。土石流の発生・発達域は一般的に急勾配であり，物理メカニズムからは不飽和土石流の存在が推定されるが，現地で観測した報告はほとんどない。しかし，土石流の発生・発達域における飽和・不飽和土石流の発生実態を明らかにしない限り，発生流下予測を適切に行うことはできない。そこで，本研究では土石流段波の波高と飽和帯の厚さの比を観測することで，飽和・不飽和土石流の流下形態を調べた。その結果，土石流段波の発生場所が上流であるほど不飽和土石流段波が発生しやすい傾向がみられた。, 本研究では科研費(18H02235，18K18917，17H02029)の助成を受けたものである。

土石流の発生には降雨による水の供給とともに，土石流材料となる土砂の存在が必要である。そのため土石流の発生予測には土砂生産（種類やタイミング）とそれに伴う不安定土砂の堆積状況の変化を把握する必要があるが，それらに関する研究事例は少ない。そこで，本研究では大規模崩壊地である富士山大沢崩れにおける山腹からの土砂生産及び渓床堆積物の量に注目し，土砂生産プロセスとその特徴，および生産された土砂の渓床での堆積厚と土石流発生箇所の関係の解明に向け，既往の航空レーザー測量成果の解析を行った。

2017 年九州北部豪雨では，氾濫，土石流，斜面崩壊による被害が多く生じた。北野平野の氾濫は，自然堤防は非浸水か浅い浸水，後背湿地と旧河道は深さ1 m を越す浸水となった。氾濫時の水深は氾濫原の微地形を反映し教科書的な被害となった。三郡山地南端部では，表層崩壊や地すべり性崩壊起源の土砂が土石流化し，家屋，河川施設に多くの被害が生じ，また複数の学校が被災した。被災した各学校は周囲に比べ小高い豪雨災害には比較的安全とみなされる地形に設置されていた。しかし地形判読の結果，各学校は，未離水の地形では堆積，離水した地形では河川の側方侵食に伴う被害を直接受けており，また学校周辺の通学路も氾濫被害や土砂災害を被った。それら被害も学校の災害対応を困難にした。各学校での聞き取り結果から，山地に近い方が警戒対応は早いが，全児童・生徒下校に要する時間は，経路被災の影響で時間を要したことが分かった。また未離水の地形に注意する施設配置の重要性も分かった。したがって学校安全には，校地周囲の詳細な地形区分に加えて，通学路を含んだ包括的な地形区分の双方を必要とし，学校に止まらず校区全体を見据えた災害対応計画が求められる。

土石流発生域である荒廃渓流源頭部においてインターパルカメラにより土石流段波の撮影を行い，発生・停止位置の読み取りを行った。またUAVを用いて渓床堆積物の堆積状況を把握し，流動状況との関係を検討した。その結果，段波が発生・停止しやすい区間があることが明らかとなった。発生しやすい区間は流域面積の大きな支流の合流地点下流側であり，渓床堆積物が3～4mの地点に多くみられた。一方，停止しやすい区間は厚い場合と薄い場合の両者がみられた。堆積物の厚い地点では堆積物の間隙に土石流中の水が浸透したため，薄い地点では緩傾斜となったために土石流が停止したと考えられる。

富土山では大沢崩れなどにおいて度重なり土石流が起きてきた。土石流の発生時期は他の多くの地域で土石流の確認される梅雨～台風ではなく，春と晩秋に発生しており，この特性には凍土が関係するとされている。本研究では大沢崩れを対象に，地温の季節変化の観測と積雪の写真画像判読の結果に基づき，凍土形成時期の推定手法を導いた。その手法を用い過去の降雨イベント時の凍土の有無を推定した結果，秋から春にかけて凍結が進行する時期には最も小さい雨量で土石流が発生し，地表面から融解のすすむ初夏にはより大きな降雨が発生に必要となることが分かった。凍土のない時期には土石流の発生に最も大きな降雨を必要とすることがわかった。

We demonstrated to determine the location and origin time of the debris flow using the ground motion data recorded with short period seismometers around the Yake-dake volcano and Kamikochi area, central Nagano prefecture, Japan. Seismic waves radiated from the debris flow are assumed as the surface wave and their location and origin time are determined so that RMS of the difference between theoretical and observed amplitude of the seismic signal are minimized by grid search method. We applied this procedure to the ground motion data of the debris flow that occurred near Ubuya-sawa valley, Kamikochi area in June 23, 2011 and could determine the location and time which well coincide with other filed investigations. We suppose this method can be one of the powerful tools to determine the location and the origin time of the mass movement phenomenon such as not only debris flow but also pyroclastic flow around the volcanoes.

大規模崩壊地から流下する土石流は，下流での直接的な被害を引き起こす場合があるため，流下規模の推定が防災や流域管理において重要だと考えられる。しかしながら，複雑な地形を有する大規模崩壊地での土石流の動態は，未だに理解が不十分である。そこで，大規模崩壊地（静岡県大谷崩）において，土石流と雨量の観測，土石流発生前後の地形測量を実施し，土石流の発達と地形変化の関係について検討した。その結果，土石流発生後には，土石流による侵食や堆積，支流や側岸部からの土砂供給によって複雑な地形変化が生じることが分かった。また，この地形変化は，その後の土石流の発達に影響を及ぼしていると考えられた。

Gullies and lobate deposits commonly occur on the flanks of craters and dune foresets on Mars. These topographic features are thought to have been formed by debris-flow processes. Debris-flow processes suggest the existence of liquid water on the surface of Mars, which is believed to have an extremely cold and dry environment. Debris flows occur when masses of poorly sorted sediment, agitated and saturated with water, surge down slopes in response to gravitational attraction. Thus, recent activities of debris flows imply the existence of liquid water phase materials on the Martian surface. However, the dry granular flow caused by a slope avalanche can also form gullies and lobate deposits, which resemble debris-flow deposits, so there are still uncertainties over the occurrence and origins of liquid water on the modern Martian surface. This study proposes a method for estimating debris-flow properties, in order to distinguish debris-flow processes on Mars. Preliminary results suggest that a lobate deposit on Mars can be formed by a debris flow that shows flow properties similar to water-saturated debris flows on the Earth. If rheological parameters of the flows can be determined from the surface morphology of lobate deposits, it would be helpful for distinguishing debris-flow processes from dry-granular flows. Although our method is in the course of development and it is still difficult to determine flow types from rheological parameters alone, future field surveys and experimental studies will provide criteria for identifying debris flows., 特集号：火星表面の地形プロセス 第III部：火星の水に関連する地形プロセス

本稿では，情報提供により新たに見いだした10 基の広島県内の水害碑の特徴について記載した上で，県内における近世の後半から現在までに建立された50 基の水害碑の歴史的変遷を明らかにする。県内の水害碑の全50基の属性（建立年，碑の縦横比，使用している文字，碑文の内容，文字数）を整理した結果，明治前～中期と，1950年代の二つの時期で碑の属性が大きく変わることが明らかになった。明治前～中期以降から1950年代までの碑は，縦長からなること，漢文や漢字片仮名交じり文からなること，被災や復旧に関する情報が豊富であること，災害からの復旧に尽力した個人を顕彰するものがあること，天皇からの下賜金を示すものがあることの特徴を持つ。1950年代以降の碑は，漢字平仮名交じり文からなること，被災や復旧に関する記述が少ないこと，慰霊を建立目的とする碑が多くなること，70年代以降には横長の碑が認められることの特徴をもつ。, The inscriptions on 10 stone monuments related to flood or debris flow disasters in Hiroshima Prefecture, southwest Japan, were described. In total, there are 50 monuments in Hiroshima Prefecture based on our previous data and these additional data. Two turning points in the 1880s and 1950s were recognized based on the characteristics of the monuments in terms of their inscription contents, volume of contents, ratio of height and length of the monuments, and use of written language. Few monuments were built before the 1880s and their contents were less informative. Monuments erected from the 1880s to the 1950s were taller; their contents were characterized as detailed information relating to damage or restoration and were inscribed using kanbun, Chinese characters only, or kanji characters with katakana. The inscriptions on some monuments expressed residents’ appreciation for solatium from the Emperor or honored a person who contributed to the restoration after disaster. Fewer monuments built after the 1950s acknowledged disaster damage or restoration, and their contents were less informative, but more monuments were memorialized victims with a short message. The characters inscribed on these monuments were kanji with hiragana. Wider monuments were observed after the 1970s.

Debris flows were occurred in Yagi 3 Chome, Asaminami, Hiroshima on 20 August 2014. The geology around Asaminami area is granite which has many joints and is easy to be weathered. Hence, the permeability of the seepage is high and fine sediment is easy to be produced. In this study, the horizontal two dimensional debris flow model considering the both the laminar and the turbulence flows is developed. Subsequently, the model is applied to the debris flow occurred in Yagi 3 Chome, Asaminami, Hiroshima and discussed the applicability of the model. The differences of the horizontal inundation areas in the residential area between the simulated results and the field data are discussed and it was found that the horizontal distribution of the sediment deposition of the coarse material is reproduced well. When the houses are considered in the analysis, sediment deposited in the upstream region of the houses and the inundation area is reduced.

[日本環境学会 第41回研究発表会] 2015年6月20日-21日, 龍谷大学, 主催:日本環境学会

平成25年（2013年）9月16日，台風第18号にともなう雨により小黒川で土石流が発生し，県道や林道，橋に被害が生じた。土砂の流出・堆積状況や構造物の被害状況を踏査したところ，礫や流木による橋の閉塞，損傷が見られ，迂回した流れによる橋の取り付け道路や護岸の洗掘や，道路上での土砂や流木の堆積が見られた。右支渓の細沢では，新規に発生した表層崩壊は限られており，渓流内の不安定土砂の再移動が土砂生産の主要因と考えられた。小黒川本川での渓岸崩壊の発生は少なく，河道内の不安定土砂の再移動により土石流が発生したと考えられた。礫や流木による橋の閉塞や損傷，洗掘による道路の損傷を軽減し，災害後速やかに復旧するためには，橋の上流での流木抑制対策や，橋の取り付け道路と護岸の強化が必要と考えられる。, Article, 信州大学農学部AFC報告 12: 91-98 (2014)

本研究では，広島県内の土石流や洪水に関する石碑の碑文の内容を整理・集約した。特に，漢文で刻まれた碑文の内容は理解することは難しいため，碑文を現代語に訳した。広島県では1909（明治42）年から現在までに水害碑が少なくとも38基建立されている。概して，第二次世界大戦前までの石碑は，災害の様子，復興の過程に関する詳細な情報が記述されるものが多い。一方，戦後の石碑は，災害の概要を端的に伝え，慰霊や復旧記念を目的とするものが多い。水害碑は，被災地の位置や被災当時の様子を，地域の住民に伝えることができる防災教育に資する媒体であり，本稿はその一助となると期待される。, We examine contents of the inscriptions on all of the stone monuments related to flood or debris flow disasters in Hiroshima Prefecture, southwest Japan. Because it is difficult for people today to understand the meaning of the inscriptions, which were written in classical Chinese, we translate those in modern Japanese. At least 38 monuments were erected in Hiroshima Prefecture during the 106 years between 1909 and 2015. The contents of inscriptions from before World War II and during the war include plentiful information related to the process of erecting the monument, and details on disaster damage and restoration work. The contents inscribed on the monuments built after the war have mainly eulogized disaster victims or memorialized restoration work, and include only brief information on disaster damage. These monuments have the potential to inform local people about the situation and areas affected by past disasters. This research contributes to education for disaster prevention by increasing awareness of past disasters.

大規模土石流の発生域である富士山大沢崩れにおいて，過去に行われた航空レーザー測量の成果と過去の土石流の発生履歴から，土砂生産から土石流の発生・流出までの一連の過程を検討した。その結果，大沢崩れ斜面部では崩落（崩壊）と凍結融解による土砂生産がおこなわれており，谷底部では土石流やスラッシュ雪崩に伴う土砂流出がおこっていた。スラッシュ雪崩流下後は，土石流と異なる谷底部の侵食形状が確認される。それには凍結土層によりできるすべり面が関係していると考えられる。

To examine effects of spatial distributions of rainfall on local occurrence of debris flow and flash flood, we observed stream discharge by interval cameras and conducted hydrological simulations with X-band rainfall radar data in four catchments in Sakurajima Island. Hydrological processes were simulated for two rainfall data; rainfall data in downstream areas (Case 1) and upstream areas (Case 2) of each catchment was applied for whole area of the catchments. Debris flows generally occurred when very strong rainfall intensity was observed in upstream areas of the study catchments. Simulated stream discharges of Case 2 were more consistent with occurrence of debris flows than those of Case 1. The simulation results also suggested that concentrations of overland flow into gullies were essential for occurrences of debris flow.

インドネシアのメラピ火山は，2010年10月26日に噴火し，その後11月まで大小の噴火が継続した。火砕流や土石流による死者は約400人にのぼる大災害であった。生産土砂量は１億４千万m3と推算されており，それらは火砕流または火山灰として南斜面と南西斜面に流出した。著者らは噴火後2010年11月，12月，2011年1月および2012年1月に調査を行い，とくに，火砕流が流出した南斜面流域と火山灰が流出した南西斜面流域での土砂災害の違いに着目して，その原因，特性，対策について検討した。その結果，南斜面では，火砕流の流下・堆積による河川の上流部での地形変化により，降雨流出特性が顕著に変化し，これまで洪水の少なかった河川で洪水による橋梁の流失が生じたことや，火山灰が堆積した南西斜面では，火山灰堆積物のクラスト化によって降雨流出率が増加したことが原因で大洪水が発生し，土砂災害が生じたと考えられる事例があることがわかった。, Eruptions of Mt. Merapi, Yogyakarta, Indonesia produced a lot of pyroclastic flows in 2010. The pyroclastic flows directly killed more than three hundred people in south slope area and the topographical change due to the pyroclastic flows caused some severe floods in Opak River where little flood had occurred before the eruption. The widely deposited volcanic ash on south-west slope caused several large floods up to the end of rainy season in 2011. Particularly, the change in rainfall runoff process due to the deposition of volcanic ash seems to be one of the reasons why the large floods occurred frequently after the eruptions. As a result a lot of infrastructures such as roads, bridges and sabo structures were severely damaged in the tributaries of Progo River and Opak River.

土石流ブレーカーの主な機能は，土石流の先端部を効率的に停止させるものである。また，狭い地域に設置可能，単価が安い，デザインが簡単である，修理が容易という特徴がある。しかし，現在では土石流ブレーカーのメカニズムは，まだ十分に説明されていない。この論文では，土石流ブレーカーに関する基礎的な実験を実施し，そして数値モデルによりその実験の検証計算を実施している。そして，それらの結果から，デッキサイズの変化による圧力変化の方法を提案している。その結果，最適なサイズとデッキ幅，砂の最大直径，幾何標準偏差の関係を明らかにしている。また，数値モデルの計算結果では，デッキ上の移動距離と堆積の高さは実験結果とよく一致する結果が得られた。, Main function of debris-flow breaker is effectively stopping a debris flow front. Debris-flow breakers have advantage not only to reduce the energy but also to create suitable narrow area, cost-efficient, simply designed, easily repaired and maintained. However, the mechanism of the debris-flow breaker has not been explained. In this paper, fundamental experiments and numerical simulation are conducted to investigate debris-flow breakers. In addition, a methodology is proposed to assess the suitability of a variable deck size and change of pressure on the deck according to separation of water. As a result, it has been acquired as relationship between optimum sizes and width of deck, maximum diameter and geometric standard deviation for sediment A, B and C. Furthermore, the simulated results of the travel length and deposit thickness on the deck are also compared with experimental results.

リエカ市に河口をもつリエチナ川はクロアチアの典型的な海岸カルスト地域を流れ、急流な河道をもつ代表的な河川である。河道の流域中央部は渓谷の最も不安定な箇所で地滑り災害の危険性が高い。ここでの岩盤移動は主に炭酸塩岩とフリッシュ岩の接触によっておこる。この渓谷の両岸斜面では落石と地滑りの発生が記録されている。これらを考慮するとリエチナ川の河道が落石や地滑りにより閉塞され、洪水イベントが発生する可能性がある。強い降水や地震の発生などは落石や岩石滑りの引き金となり天然ダム崩壊などによる土石流発生の可能性がある。本論文では甚大な規模の斜面崩壊やそれに関る土石流が発生したシナリオおよびモデル構築に関する基本的なアプローチを示す。, Rjecina river is an example of a large torrential watercourse typical for the coastal karst zone of Croatia with its river mouth in the center of Rijeka city. The central part of the watercourse is the most unstable part of the valley, with the highest degree of geological hazard. Here, mass movements are occurring mainly at the contact of carbonate rocks with the flysch rock complex. There are historic data of few rockfalls and landslides on both slopes of the valley. A potential geohazard event could involve movement of slope deposits towards the channel of the Rjecina River. Heavy precipitation and/or earthquakes may be potential triggers of rockfalls and rockslides. So there is a possibility of massive scale landslide occurrence and consequently it can cause several scenarios. Possible scenarios would be investigated furtherly during the Croatia-Japan Joint Project. The paper shows the basic modeling approach for Scenario for Massive scale debris flow occurrence.

本研究では急斜面の土石流の実験水路を用いた。土石流における大きいな被害と多い死傷者を引き起こすのことがあるので、大きい粒子運動の特性を実験するのは、重要である。 この研究は2つの異なった粒径(10mmと2.5mm)の土石流開発のメカニズムを示している。この研究は1つの傾斜度(25º)を使っていた。一定の流量(3.0l/s)が7秒の持続時間に供給された。粒子運動は、目視により個々の粒子粒の運動特性を得るのに、高速ビデオカメラ(HSVC)を使用することによって分析された。水文土石流−2D モデル(HD2DM)は、ラグランジアンの沈殿物の粒子の追跡の数字の実験に基づいて開発された。それぞれの粒子運動をたどるHSVC結果は、HD2DMシミュレーションの結果と比較した。, The steep-slope debris flow experimental channel was employed. It is important to investigate the characteristics of larger particles movement in debris flow as it can cause major damages and casualties. This research demonstrates the debris flow development mechanism between two different particle sizes. Two different sizes of particles were 10mm and 2.5mm. This study involves one slope angle which is 25º. A constant discharge (3.0l/s) was supplied for the duration of 7 seconds. The particle movement was visually analyzed by using high speed video camera (HSVC) to capture the movement characteristics of the individual particle grain. A numerical model entitled as the Hydro-Debris 2D Model (HD2DM) was developed based on the Lagrangian sediment particle tracing numerical experiment. The HSVC results tracing each particle movement were compared with the HD2DM simulations. Analyses using the HSVC fully demonstrated the mechanism of the debris flow. Velocities in upper layers are faster than in lower layers and the larger particles move ahead. Similar characteristics can be observed in the numerical simulation using HD2DM.

本研究は石灰質による流下土石流と土石流扇状地の形成過程を宇治川オープンラボラトリに設置された急勾配水路を用いて解析を行なったものであり、土石流発生と発達過程における分級および、扇状地における粒度分布解析結果を明らかにするものである。本研究においては混合粒径土石流の分級を議論する基礎実験として二つの異なる流径(2.5mmと6mm)を用いた土石流扇状地の形成実験と高速ビデオカメラを用いた粒子追跡を行なった。扇状地の形成過程の初期段階において荒い流径粒子が前方に集中し、これらが扇状地の発達に影響を与える事を明らかにした。, In the recent decade, several debris flow events have occurred and caused hundreds of deaths, injured people and damaged many facilities. Consequently, there is a strong need to devise a method to evaluate the possible debris flow hazard areas. To comprehend precisely this problem, this study sets up debris flow experimental channel at Ujigawa Open Laboratory. The model apparatus are consisted with three main components: a flume open channel, a deposition board and a water intake box. To understand the particle segregation and movement mechanism of the limestone grain (2.5mm and 6mm) flow, a high-speed video camera (HSVC) is used to capture a video footage during short intervals of 0-40s. Besides using HSVC, video recordings of the tests were performed to analyze debris flow characteristics. This paper presents about the routing of limestone grains at two different slope angles which of 18° (mild) and 25° (steep). Results of the deposition patterns for each case are discussed.

流木を含む土石流の特性及び, グリッドダム・スリットダムに代表される透過型砂防ダムによるこれの捕捉過程をシミュレートする二次元数値解析モデルを構築した。数値解析モデルは, 土石流のオイラー的挙動解析法と流木のラグランジュ的運動追跡法の組み合わせにより構成しており, 流木が存在する座標の変動成分及び流木の回転角速度については確率的にこれを与えた。透過型砂防ダムによる流木の阻害については, 流木の幾何学的状態及び確率的手法により評価を行った。数値解析により, 実験結果と適合する流出量・堆積量・下流端での流木通過率を得た。, A two-dimensional numerical model is developed for computing the characteristics of debris flow with driftwood and its capturing process by open type check dams such as grid or slit type check dam. A numerical model is developed with an interacting combination of Eulerian expression of the debris flow and Lagrangian expression of the driftwood, in which the fluctuation components of the position and the rotational angular velocity of the driftwood are dealt with stochastically. The jamming of driftwood on grid or slit type check dam is evaluated based on the geometric conditions and probabilistic approaches. The simulated results of outflow discharge, sediment discharge and the percentage of driftwood outflow at the downstream end of the flume agree well with the experimental results.

土石流メカニズムの理解と予防策についての研究は，流域内の土砂管理や土砂災害の防止のために重要である。通常，透過型の砂防ダムは土石流を貯えることにより土砂災害を防ぐものとして使われている。砂防ダム上流での土石流堆積過程及び通常洪水流による堆積土砂侵食のメカニズムを研究するため，数値解析と実験を行った。砂防ダム上流での土石流堆積を計算する新たな式を明らかにした。解析と実験は不透過型砂防ダムと格子型砂防ダムを用いた。, The understanding of behavior and mechanism of debris flow, and the study of preventive measures are very important in order to manage the sediment disaster in the river basin and prevent the downstream hazards. A check dam is commonly used for preventing the sediment disaster due to debris flow by storing the harmful sediment discharge. The numerical simulations and experiments have been carried out to investigate the mechanism of debris flow deposition process upstream of a check dam, and flushing out of deposited sediment due to erosion process by a normal scale flood flow. A new deposition equation to calculate debris flow deposition upstream of a check dam is also developed. The simulations and experiments have been performed using closed type and grid type check dams.

A sediment disaster warning information system was established nationwide in September 2005. The system provides information to local governments for use in their disaster prevention and emergency evacuation activities. The system was used in Kagoshima for the first time in 2005 during Typhoon No.14. A survey was undertaken to see how the sediment disaster warnings were used by the self-governing bodies in Kagoshima Prefecture and the residents of the Kotani District, which suffered damage from a debris flow. The survey revealed that 40% of the self-governing bodies utilized the sediment disaster information provided by the system during the typhoon. The residents of the Kotani District heard the sediment disaster warnings but did not take refuge, preferring instead to act with caution.

Between 15^ and 24^ of July in 2006, there was a heavy rainfall, in several areas of the central western region of Japan. It was the biggest rainfall in recorded history in the Suwa and Kami-Ina areas of Nagano prefecture. From results of a study in Okaya city which was affected by a debris flow, rainfall was the main focus as it was the direct cause of the Okaya sediment disaster. This study is to analyze by monitoring rainfall data to predict future disaster risk in Okaya. After collecting official rainfall data and forecasting of the risk level of sediment disasters and then determining the critical line for warnings of sediment disaster, it was concluded that there was no doubt this disaster could have occurred in any part of the Okaya area due to the heavy rainfall.

奈良県十津川村の人工林施業域において、土石流発生履歴の異なる42の源頭渓流を対象に、河道内土砂量、ハビタット要素の多さ、ミクロハビタット構造を調査した。土石流発生履歴と河道内土砂の関係は見られなかったが、土石流によって倒木、落葉枝ダムや堆積卓越型ミクロハビタットが減少することを明らかにした。底生動物群集を規定するミクロハビタットの多様性は土石流発生の履歴とともに変動することを示した。, Disturbance plays key roles maintaining species diversity and ecosystem function in wide range of ecosystems. We examined relationships between debris flow history and stream habitat structure (in-channel sediment deposits, abundance of streambed elements, occurrence of different types of microhabitats) using 42 headwater streams with different histories of debris flows in a managed forest watershed, Totsukawa, Nara. In-channel sediment deposit was highly correlated with channel slope and valley width, and related little to debris flow history. Number of large woody pieces and woody debris dams were more in streams with older occurrence of debris flow. Erosive microhabitats such as bedrock, splash zone, moss mat were common in all streams, while depositional microhabitats such as mud and leaf pack occurred only in streams with old (>30 yrs) debris flow, and sand was absent in streams with very old (>50 yrs) debris flow. These results indicate that stream habitat diversity is dynamically maintained in a repeated manner through debris flow history.

Mie Prefecture suffered from water-related disasters due to the Typhoon T200421 on September 29, 2004. Nine persons died, about 70 houses were destroyed by debris flows, slope failures or landslides, and more than 5,000 households were inundated. In this work, first, we analyze meteorological data and conclude that the heavy rainfall were caused by the existence of a stationary front into which the typhoon supplied warm humid air masses, and the orographic conditions over Mie. Secondly, we estimate the return period of t-hour (t＝1, 2, 3, 6, 12, 24 hours) precipitation at four locations in the prefecture. Finally, disasters due to landslides or debris flows in Miyagawa Village are overviewed and discussed. The above-mentioned meteorological analysis shows a very close relationship between the locations of heavy precipitations during relatively long terms (say 24 hours) and the occurrence of debris flows or landslides., 地球規模水循環システム予測値のスケールダウンと予測の不確実性低減手法の開発