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流砂漂砂系において重要な役割を果たしている流体と堆積物の複雑な相互作用について、最近の進歩および課題を概観している。流域規模における降雨流出と土砂流出については、分布型モデルの進歩により、実問題の要請に応えられる精度での予測が可能となってきている。その実例として、インドネシア国Lesti流域における土砂管理や土地利用計画に繋がる研究成果を紹介している。水制等を活用した河川環境再生には、高精度かつマルチスケールの流水/土砂挙動の予測が必要になる。木津川流れ橋エリアの河川環境再生プロジェクトに関連して、最新の多次元流水/土砂挙動解析コードの適用例を簡潔に紹介している。さらに、海岸域における研究課題として以下のようなテーマをとりあげ、今後の研究の方向性について言及している： 漂砂系の土砂収支におよぼす海底谷の影響、イベント過程を見据えた岸沖方向の堆積物輸送の再評価、海浜環境のリモートセンシング、内湾―海峡―外洋系をつなぐ海水循環ダイナミクス、津波災害環境の復原に繋がる海域音波探査/堆積学的調査法のポテンシャル。, This paper overviews some issues of complex fluid-sediment interactions that characterize the multi-scaled nature of sediment routing systems. It first demonstrates the capability of grid-based modelling for precipitation-derived processes of water flow and sediment transport in a hilly watershed (the Lesti River basin, Indonesia). The predicted and observed performances highlight the importance of vegetation cover in the sediment management that may relate closely to land-use practices. The paper then focuses on advanced numerical modelling for fluvial sediment dynamics, with particular reference to the reappraisal of groin systems in river restoration. There follows a concise discussion of the linkage between fluvial and littoral sediment delivery. Reviews are then directed on studies of coastal dynamical environments. The themes taken up include: the evolution of beach erosion such as occurring in Ogata coast; the coastal ocean dynamics pertaining to nutrient transport; and tsunami sedimentation - an attempt for exploring tsunami-induced submarine deposits.

本稿は，21世紀COEプログラムの中で「山地・河川・海岸系における物質動態に関する研究」の成果を一昨年および昨年度に引き続き第3報として取りまとめたものである。穂高砂防観測所をはじめとする隔地観測所・実験所で実施されている観測・実験を通して、山地から河川、さらに海岸・海域に至るまでの物質動態、とくに土砂動態を中心に取りまとめている。山地部では、裸地斜面からの長期的な土砂生産量を観測し、凍上・融解による土砂生産と粒度分特性が明らかになってきた。また、模型斜面を用いた豪雨時表層斜面崩壊の実験と予測モデルの検証並びに山地部での降雨・土砂流モデルの構築と観測データによる検証が行われている。水害調査にもとづく谷底平野および沖積平野における水害地形と河道変動に関する検討や、没水時の水制による局所洗掘に関する3次元流と河床変動解析法の開発も行われ、その概要が示されている。また、暴風時の沿岸流の特性や海浜風や降雨に与える黒潮などの暖流の影響などが現地観測やシミュレーションを通して明らかにされている。, This manuscript describes some of the recent research results obtained under the 21st COE project on long-term observation of sediment yields in the mountain regions, development of numerical simulation model on riverbed evolution, characteristics of flood plains and its formation by the flood, and fluvial sedimentary features in flood-stricken areas. Moreover, temporal variation of observed longshore current velocity and the relationship between the current velocity and external forces (winds and waves) is discussed, especially under storm conditions. And also, effects of Kuroshio warm current sea surface temperature on coastal wind and precipitation fields are simulated by meso-scale meteorological model MM5.

滋賀県南部に位置する田上山地の若女裸地谷の裸地斜面において，凍結融解と土砂生産現象の詳細な観測を行なった。観測期間は，2004 年12 月から2005 年4 月までであり，その間に気温，地表面温度，基岩温度（ 深度10，25，50 cm）を10 分間隔で連続計測した。その結果，観測期間中に凍結融解が繰り返し起こり，基岩中の温度が0℃以下となる凍結層は， 少なくとも10 cm の深度まで達することがわかった。また， この凍結融解作用によって土砂が活発に生産されることが確認された。さらに，基岩上の土砂被覆が凍結融解作用を緩和することが示唆された。, A detailed field observation was conducted to elucidate mechanisms of freeze and thaw process and following sediment yield on a bare slope in Tanakami Mountains, southern part of Shiga Prefecture. During the observation period (December, 2004 - April, 2005), air, surface and subsurface (10, 25, 50 cm depth) temperatures were continuously measured with 10 min interval. From the observation results, it was indicated that the freeze and thaw cycle occurred repeatedly, and the frozen zone (temperature < 0 ℃) reached to the depth of 10 cm. It was confirmed that the sediment yield occurred due to the active freeze and thaw process, and stopped at the end of the observation period when the freeze and thaw cycle also stopped (April, 2005). It is also suggested that the bedrock surface cover affects to the sediment production due to the freeze and thaw processes.

著者らは物理機構に基づく土砂生産のモデルを開発し，精度の高い土砂生産量の短期・長期予測および流域全体のモニタリングを可能にしようとしているが，最終的にはこれを土砂生産マップに組み込み，土砂生産量の予測情報，モニタリング情報を提供できるようにしたい。モデルの開発に当たっては，土砂生産特性を十分考慮することが重要であり，本研究では高原川流域を対象にしてそれを検討する。その結果，土砂生産量は斜面の凍結融解と密接な関係にあることがわかった。, We are developing a sediment production map informative for the integrated sediment management. The map based on a sediment production model can be used for predicting and monitoring the sediment production over a watershed. To make the map much more effective, the process of sediment production should be fully introduced into the modeling. In this paper, we have described the characteristics on sediment production based on a long-term observation data in the Takahara river basin. The data have shown the sediment production is dependent on the rainfall events, but the volume is dependent on the freezing and thawing process on the weathered slope. The sediment production processes over a year was described on the basis of observation data.

流域と海岸域を繋ぐ流砂系の本質を理解するには、流体―堆積物系のダイナミクスに関する健全な知識が不可欠である。本報文では、流域スケールの流出解析と飽和/不飽和浸透解析を結合した豪雨時の斜面崩壊発達過程の解析をはじめ、表面侵食による山腹斜面からの土砂生産実態の観測、河道安定に深く関わる水制周りの三次元的な流況と河床変動の解析及び室内水路実験による検証、超過洪水による堤防破堤とそれにともなう三次元重力流の解析、そして台風来襲にともなう後浜への大規模な砂の打上げ現象等に関する研究成果を論述している。, This paper focuses on complex fluid-sediment interactions that may characterize the dynamical nature of sediment routing systems. Particular attention goes to storm-scale phenomena, and trends of mesoscale modelling are briefly reviewed first. Discussions are then directed on specific topics, which include: long-term observations of surface erosion on a hillslope; basin-scale analysis for predicting the development of shallow landslides in a heavy rainfall event; Numerical and physical modelling of the three-dimensional flow field and bed deformation around spur dykes, with implications in river stabilization; flow-out modelling for assessing the impact of levee breaching; and remarkable onshore transport of beach sand in a typhoon event. Collectively, the coverage emphasizes the importance of integrated analysis procedure for treating the three-dimensional nature of fluid-sediment interactions.

流域土砂管理においては，土砂生産の実態を時系列的に解明し，生産土砂の量と質を予測するモデルを構築することが重要である。本研究では，高原川流域で行われている個々の裸地における土砂生産の直接的観測および一つの流域における間接的な土砂生産量の解析から，凍結融解や降雨に起因した土砂生産の特性について検討した。その結果，通常時，凍結融解によって作られる土砂生産場の状態が生産土砂量に大きな影響を与えるため，生産土砂量は降雨量とあまり相関がないことなどが示された。, Various phenomena such as turbid flow, sediment transport, riverbed erosion and sediment deposition influencesthe river environment including eco-system along the sediment movement path. In the integrated sedimentmanagement for these phenomena, it is very important to consider the sediment production process as time series ofproduction events. Moreover, it is also important to develop the predicting model of the sediment production. In thisresearch, the characteristic of the sediment production due to the freezing and thawing and the rainfall is examinedfrom the data analysis of the sediment production volume observed in the Takahara river basin. As a result, thesediment production volume is strongly dependent on the number of freezing and thawing events.

流域と沿岸域を繋ぐ流砂系のとらえ方について、最近の進歩を概観している。分布型流出モデルの実流域への適用と貯水池堆砂実績による検討例に基いて豪雨イベントによる土砂流出過程の重要性を指摘し、ついで、漂砂収支解析法の現況にふれ、沖合境界への堆積物流束、特にストーム条件下での堆積物流束の実態把握の重要性を指摘している。さらに、流体―堆積物系のダイナミクスに焦点を当て、土砂流出と河川生態系の関わりを示す現地観測、粘着性／非粘着性堆積物の混合体に対する流送モデルの提案、伝統的水制工による土砂制御機能の再評価、ならびに液状化堆積物の水中重力流れ機構の解明について論述している。, This paper starts with an overview of recent developments pertaining to sediment routing systems that may connect fluvial, estuarine and coastal environments. It discusses sediment runoff analyses on a basin scale and methodologies for developing a budget of littoral sediment. It then focuses the discussion on recent findings obtained through collaborative research in the framework of a Center-of-Excellence program. The topics covered include the following: field observations of offshore-going sediment fluxes in the surf zone; reservoir sedimentation; an interrelationship between the riverbed morphology and habitat of a class of fish as influenced by sediment runoff; modeling of the transport of mixtures of non-cohesive and cohesive sediments with emphasis on wash load; reappraisal of traditional flow-control structures for river stabilization; and the dynamics of sediment gravity flows. Collectively, the coverage emphasizes the importance of addressing highly nonlinear fluid-sediment interactions.

本研究では，河川小流域において濁度の連続観測や源頭部での生産土砂の河道への供給現象のビデオ観測を行い，上流で起こる土砂供給イベントと下流で観測される濁度の時間変化の関係，濁度，流量，降雨量の相互関係，濁度の変化と河道内の土砂移動現象の関係について検討した。この結果，濁度観測および水文観測により，土砂動態，すなわち，土砂供給イベントの生起，供給量，土砂移動過程が間接的にモニタリングできることを明らかにし，濁度を指標とした土砂動態のモニタリング手法の可能性を示した。, The volume and the timing of sediment supply from a source point into a torrent are the essential parametersgoverning the sediment movement in the watershed. However, it is very difficult to measure them directly. Washload may be used as an index indicating indirectly both of the volume and the timing because the occurrence ofwash load is closely related to sediment movement. In this paper, we have studied this point from the fieldobservation. We have introduced a monitoring system of sediment movement in an experimental watershed.Thevideo camera system is recording the erosion process of the deposit and the sediment transportation in theheadwater area. The turbidity meter and the flowmeter have been installed at the about 1000 m downstream of thevideo camera site. The observation result has shown that the situation of sediment movement can be inferred fromthe data of turbidity and water discharge.

避難計画を立てる場合, 最適な避難地や避難経路を行政側だけでなく地域住民が周知しておくことが重要である。本研究では, GISのネットワークデータを利用した住民の避難行動の解析方法を示すとともに, 実流域を対象として老人や子供歩行速度を考慮した避難行動の解析を行って避難所要時間を求めている。さらに, これに基づいて新たな避難施設を設置した場合の効果についても検討している。, Non‐structural countermeasures, such as residents living in the hazard area taking refuge before the onslaught of a debris flow, is effective for saving lives.A simulation method for evacuation is presented that is based on a refuge network, built using the GIS (Geographic Information Systems, ARC/INFO).Visual display of the act of evacuation is very useful for both the administrators and residents of the basin.

中国雲南省の蒋家溝を対象に, 粘性土石流のメカニズムと土石流対策に関する観測調査を行って, 土石流が降雨の発生時刻からかなり遅れて発生すること。土石流が, 多数のサージが間欠的に流下するという一連のイベントからなっていて, その間欠性は, 降伏応力を用いたモデル, 天然ダムの決壊モデル, 流れの不安定性に基づくモデルを用いて説明が試みられていること。砂礫の濃度が著しく大きいにもかかわらず, 土石流が流れ易いこと。流動中の土石流には栓流が存在しないこと。さらに, 蒋家溝の中下流域での, 土石流発生に伴う地形変化が災害発生ポテンシャルを高めていること。禿げ山化した山地の緑化が進められた結果, 土石流発生などの土砂流出抑制効果が認められたが, そのメカニズムの検討が課題であることを述べた。, The observational study on the viscous debris flows at Jiang-jia Creek in Yunnan Province, China clarified the following points. The time delay of one to five hours from the beginning of rainfall to the onset of debris flow may be ascribed to an accumulating process of slurry from tributary gullies to the main channel bottom at the source reach of the debris flow. The intermittence of debris-flow surge may be explained through the mechanism either of or a complex of an yield strength model, a model of a series of breaching of small natural dams, or a model of an instability of the flow itself. The absence of plug-flow phenomena in the viscous debris flow indicates the yield strength of the flow is unexpectedly small, and a new alternative model is necessary to explain the mechanism of viscous debris flow. The field survey of the countermeasures against debris flows in Dongchuan County over five years showed the tree-planting project at mountain slopes in these several years may have been effective in increasing the slope stability, suppressing sediment discharge and debris flows. Further study is needed to evaluate this effect of countermeasure quantitatively.

A numerical simulation method which can establish a designed debris flow hydrograph and hazards due to flooding of it under arbitrary basin and rainfall conditions are given.This method is consisted of one and two dimensional analysis. One dimensional analysis can evaluate a debris flow developing process by erosion and deposition of gully bed by surface water runoff or supply of debris and water as a consequent of landslide. Whether landslides will occur or not is one of very important factors to generate a large-scale debris flow. The effects of the landslide location and the number of landslide to the generated debris flow hydrograph are investigated. Two dimensional analysis can evaluate the process of flooding and deposition of a debris flow. This method can identify hazardous zones, examine the safety of the refuge places and routes, and give useful information about mechanism of occurrence of the debris flow hazard to the residents. This method is verified by applying to an actual debris flow.

This study describes the erosion and its relating phenomena typical on bare slopes in mountain. Erosion is characterized by various regional factors including geology, topography, weather and vegetation on slopes. The present research has been carried out considering that erosion depends mainly on the gradient and the compressive strength of slope, and the real situation of erosion was clarified through observation and survey of actual slopes in the experimental plots.

In this paper, at first, behaviors of the erosion and deposition along the stream channel are discussed in view of the measured channel variation in the Hirudani basin (0.85 kim^2).Secondly, the process of sediment transport during floods on the mountain rivers with sequential falls and pools were considered by means of the grain-size and petological classification of transported gravels in reference to the geological distribution in the basin.

In this paper, a new numerical simulation model is proposed, which can predict the sediment runoff from a mountain watershed. In the model, the watershed is composed of some units of slopes and a network of stream channels. The runoff process from each slope unit is calculated by the kinematic wave method. The process of water runoff in the channel network is calculated by one dimensional simulation model using the water discharges from the slopes. The bed variation and sediment discharge in each stream channel can be predicted by a bed-load formula. The bank erosion is considered as the main cause of the sediment supply.

In this paper, the characteristics of the pattern of mountain ravines, the variations of those patterns during a flood, the changes of those patterns before and after the floods are discussed.A relation between step-pool channel geometry and transport of bed sediment was clarified through observation of sediment transport and survey of channel patterns in the Ashiaridani creek (7.2km2) of the Jintsu river from 1971 to 1993.

Sediment yield is characterized by various regional factors including geology, topography, weather and vegetation. So many factors are relevant to the phenomena of sediment yield that prediction is rather formidable task and it needs untiring observation of the realities of the phenomena. The present research has been carried out considering that sediment yield depends mainly on the gradient of slope, and the real situation of sediment yield was clarified through observation and survey of actual slopes in the field.

Observational studies on the runoff, sediment yield and the sediment transport have been carried out in an experimental basin, the Ashiaraidani creek (6.5 km^2), which is a tributary of the Jintsu River.(1) The relation between sediment yield and rainfall, slope grade are examined, to clarify the processes of sediment yield in various slopes, taking seasonal variations as well as site conditions into accounts. (2) The relation between sediment runoff and sediment storage in the steep channel with pools were investigated in the Hirudani creek (0.85 km^2). (3) The occurrence of debris flow were investigated with attention forcused on rainfall intensity in the Shiramizudani creek (2.1 km^2).

Field survey and observation were carried out for clarifying the real situation of sediment yield on a bare slope, sediment runoff in the steep channel, and debris flow on the Ashiaraidani creek (6.5 hA), which is a tributary of the Jintsu River.(1) Based on the test slopes, sediment yield is governed by the gradient of any given bare slope, the compressive strength of soil of that slope, rainfall, and frostinduced heaving and thawing. (2) The relation between sediment runoff and sediment storage in the steep channel with pools were investigated in the Flirudani creek (0.85km^2).(3) Rainfall intensity on a small area bring about the occurrence of debris flow in the Shiramizudani creek (2.1km^2).

Electro-magnetic studies have been conducted to investigate the volcanic activity of Mt. Yakedake locating in the Norikura volcanic chain in central Japan. Preliminary results were obtained as follows;1. The measurement was made on the total magnetic force and the surface resistivity at the Shiramizudani area, the half up of Mt. Yakedake. The analitical results obtained elucidate the spatial distribution of both volcanic sediments and mud flow deposits around this area.2. The paleomagnetic method was developed to investigate the temperature conditions when the volcanic sediments were embeded. The method was applied to classify the volcanic sediments (originated from Nakao pyroclastic flow c.a. 2500 to 1500 years B.P.) into three types; pyroclastic flow deposit, hot lahar deposit and cold lahar deposit.3. Three observatory stations were established for the continuous monitoring of electric self-potential, geomagnetic total force, ground temperature and steam temperature conditions around the Yakedake area. Preliminary data observed at Nakao Station, the foot of Mt. Yakedake, show that the short-term fluctuations of the electric potential correlate quite well with these of the temperature changes of steam rising from 300 m depth. During the period of the above fluctuation, small earthquakes were observed around the Yakedake area in most cases.

Observational studies on the runoff, sediment yield and the sediment transporthave been carried out in an experimental basin, the Ashiaraidani creek (6.5 km2), which is a tributary of the Jintsu River.(1) The relation between sediment yield and rainfall, slope grade are examined, to clarify the processes of sediment yield in various slopes, taking seasonalvariations as well as site conditions into accounts. (2) The relation betweensediment runoff and sediment storage in the steep channel with pools wereinvestigated in the Hirudani creek (0.85 km2). (3) The occurrence of debris flow wasinvestigated with attention focused on rainfall intensity and local rainfall in theShiramizudani creek (2.1 km2).

The authors carried out some observation on the runoff, sediment yield and transport in asmall mountain watershed, called Hirudani Experimental Watershed, which is a tributary of theJintsu River in Gifu Prefecture, Japan. This paper presents some results of the observations onrunoff characteristics, on rate of sediment yield and transport by petrologic classification of gravels, settled and transported, and of the survey on the change of river bed before and after floods.The following interesting fact are pointed Out after studing the observations and surveyresults.1) The characteristics of transport materials reflect the process of the runoff over the sedimentsource areas.2) The process of the sediment transport in a mountain watershed is revealed throughthe distribution of the grain size and petrologic character of gravels in the transport materials.3) The river bed variations as well as the sediment yield should be detected for estimationof the sediment discharge from a basin.

The authors carried out some observations on the runoff of rain, sediment yield andtransport in a mountain watershed, called Ashiaraidani (7.2km2), which is a tributary ofthe Jintsu River in Gifu Prefecture, Japan.In this paper, the process and mechanism of sediment transport on the stream channelwere analyzed by petorological and grain-size classification of transported gravels for oneyear cycle at Hirudani experimental watershed (0.85 km2). The mechanism of occurrence and behavior of mud-debris flow were partially revealedthrough the field observation on variations of river bed, and the water balance of mud-debris flow at Ashiaraidani experimental watershed (6.5 km2).

Observational studies on the runoff, sediment yield and the mechanics of sediment trans-port have been carried out in the experimental basins, the Ashiaraidani(6.5 km2) and the Taka-haragawa(472 km2), which are tributary of the Jintsu River in Gifu Prefecture, Japan. In thisbasin all the aspects of sediment transport which appear in mountain ravines, namely, bed load, suspended load, wash load, and debris flow can be seen under various rainfall and dischargeconditions.In this paper, sediment production on bare slopes and gully walls and the behavior of thedebris fiow the stream channel and as it passes through a crib dam are discussed.

Observational research of the runoff process, sediment yield and transport have been carriedout in an experimental basin, Ashiaraidani (6.5 km2), which is located in the Northern Japan AlpsRange. In this basin all aspects of sediment transportation which appear in the mountain ravines, namely, bed load, suspended load, wash load, and debris flow can be seen under various rainfalland discharge conditions.Erosion processes of the bare slopes and gully walls and transports of gravels on the steepchannel as contact load and accompanying stream channel variations are discussed in view of theobserved facts in the Ashiaraidani. The process and mechanism of sediment transport duringa flood on the steep channels with sequential falls and pools were considered by means of thepetorological and grain-size classification of transported gravels in reference to the geologicaldistribution in the basin, and the relationships between flow rate and sediment discharge in theHirudani basin (0.85 km2) are explained as a function of sediment storage in the pools.

The study of the sedimentation system such as detachment, transportation anddeposition of sediments are necessary to develop a method for evaluating sedimenta-tion processes in a drainage basin. Setting up the experimental basin in the Ashia-raidani creek (7.2 km2) of the Jintsu river where various phenomenon of sedimentationare occurring, observational studies have been carried out since 1966 in order to in-vestigate sediment phenomena.In this study, four problems are discussed;(1) The relation between sediment yield and rainfall, slope grade and etc. areexamined, to clarify actual condition of sediment yield in various slopes. (2) Therelation between sediment runoff and sediment storage in the steep channel withpools were investigated in the Hirudani (0. 85 km2). (3) The occurrence of debrisflow were investigated with attention forcused on rainfall intensity and in-filtration in the Shiramizudani. (4) The numerical simulation of the debris flow con-trol by crib dam was made, and compared with observed data in the Shiramizudani(2.1 km2)

The authors carried out some observations on the runoff of rain, sediment yield and transportin a mountain watershed, called Ashiaraidani (7.2 Km2), which is a tributary of the Jintsu Riverin Gifu Prefecture, Japan.In this paper, the process and mechanism of sediment transport on the stream channel inHirudani experimental watershed were analyzed by petorological and grain-size classification oftransported gravels. Colored gravels were also used as the tracer to identify the characteristics ofsediment particle movements.The mechanism of occurrence and behavior of debris flow were partially revealed throughthe field observations on variation of river bed, and the water balance of debris flows in Ashiaraidaniexperimental watershed (6.5 Km2).

河川を中心とした水と土砂れきによる災害を防止・軽減するためには, 出水と土砂流出の実態を明らかにすることが必要である。とくに山地流域での土砂は降水とその流出特性, 流出土砂源の分布とそれらの特性, および河道での伝播と変形, 貯留特性に関係する複雑な現象である。著者らは, 山地における出水と土砂流出の実態の正確な把握と土砂流出機構の解明を目的として, 穂高砂防観測所において試験流域を足洗谷流域(7.2k㎡)に設定し, 上記の内容について観測・研究を行なってきた。従来の観測成果1)～6)は足洗谷流域の小支渓であるヒル谷試験流域(0.85km2)におけるものであったが, 本文では新しく流砂観測に成功した足洗谷試験流域(6.5k㎡)における観測成果についても報告している。, The authors carried out some observations on the runoff of rain, sedimemnt yield andtransport in a mountain watershed, called Ashiaraidani (7. 2k㎡), which is a tributary ofthe Jintsu River in Gifu Prefecture, Japan. This paper presents some results of the obser-vations on runoff characteristics, on rate of sediment yield and transport, and on streamchannel variations before and after floods. For the measurement of bed load during a floodin the Ashiaraidani stream channel, a newly developed equipment with tilting backets wassuccessfully used. The process of sediment transport was analyzed by petorologic classifica-tion of transported gravels.

Observational research of sediment yield and transport have been carried out in mountainbasin called Ashiaraidani (7.2km2), which is located in the Northern Japan Alps Range.This paper presents some results of the observations on runoff characteristics, on rate ofsediment yield and transport, and on stream channel variations before and after floods inthe Hirudani basin (0.85 km2). These major observational research efforts have produceda bedload equation that can be used in gravel-bed steep channels with stair-like sequencesof pools and chutes.The process and mechanism of sediment transport during a flood in the Ashiaraidanistream channel were partially revealed through the observation of flows and channel variationson the stream by the TV camera.

The sediment runoff problem in a basin is one of the most significant studies in thefield of the river environment, water resources and disaster prevention. The sedimentprocess includes sediment production, sediment transport and sedimentation down stream.These processes simultaneously or alternately occur in the several areas in the basintaking various manners responding the characteristics of the basin and the magnitudes of thegiven causes. Thus, the total sediment runoff system comprises many complex subsystemsand could be analysed as a process-response system to relate input of precipitation withoutput of sediment.The sediment production system which is one of the subsystems in the sediment runoffsystem could be analysed as a morphological system relating angle of slope to variableincluding depth of superficial material, distribution of grain size, soil texture and the externalcauses.We have conducted the observational studies for sediment runoff process in an experi-mental basin where the rate of sediment runoff is the greatest in Japan and various modesof sediment yield and runoff can be observed depending on the difference of the topographical, geological and climatic conditions in the subbasins. In this paper, measuring techniques forsediment yield are described, and the rate of sediment yield is discussed in relation to theslope angle, rainfall intensity, freezing and thawing effect, and the properties of materialsuch as grain-size distribution and conpressive strength

The objective of this study is to clarify the influence of climatic factors upon soilerosion and the processes of sediment transport in the mountain basin. The area studied inthis report is located at the Northern Japan Alps Range. Observational studies concerningsediment-processes have been conducted in the Ashiaraidani experimental basin (6.5 km2)since 1966 and in the Takaharagawa experimental basin (472 km2) since 1984.In these experimental basins, all the aspects of erosion and sediment transport whichappear in mountain basin, namely, sheet erosion, gully erosion, bed load, suspended load, wash load and debris flow can be seen under various rainfall and discharge conditions.In this paper, sediment production on bare mountain slopes and gully walls, sedimenttransport along a steep channel and the occurrence of debris flow are discussed.

Observational studies on the runoff process, sediment yield and transport have been carried outin an experimental basin, Ashiaraidani (6.5km2), which is a tributary of the Jintsu River in GifuPrefecture, Japan. In this basin all aspects of sediment transportation which appear in the mountainravines, namely, bed load, suspended load, wash load, and debris flow can be seen under variousrainfall and discharge conditions.Erosion processes of the bare slopes and gully walls, and transports of gravels on the steep channelas contact load and accompanying stream channel variations are discussed in view of the observedfacts in the Ashiaraidani. The process and mechanism of sediment transport during a flood on thesteep channels with stair-like sequences of pools and chutes in the Hirudani basin (0.85 km2) werepartially revealed through the observation of flow discharge, sediment discharge and sediment storagevariations in the pools.

Observational studies of the runoff process, sediment yield and transport have been carried outin a mountain basin, Ashiaraidani (7.2 Km2), which is a tributary of the Jintsu River in GifuPrefecture, Japan.In the Hirudani experimental basin, which is one small tributary in the Ashiaraidani, theprocess and mechanism of sediment transport on the stream channel with sequential falls andpools were considered by means of the petorological and grain-size classification of transportedgravels in reference to the geological distribution in the basin, and the relationships between flowrate and sediment discharge.In the Ashiaraidani experimental basin, transport of gravels on the channel during a floodwas investigated taking notice of the difference in the grain-size distributions in armoured bed anddebris flow deposits. The mechanism of occurrence and behavior of debris flow were analyzed bythe river bed variation before and after the passage of it and the concept of water balance.

The authors carried out some observations on the runoff of rain, sediment yield and trans-port in a mountain watershed, called Ashiaraidani (7.2 km2), which is a tributary of the JintsuRiver in Gifu Prefecture, Japan. This paper presents some results of the observations on runoffcharacteristics, on rate of sediment yield and transport, and on stream channel variations beforeand after floods in the Hirudani experimental watershed (0.85 km2).The process and mechanism of sediment transport during a flood in the Ashiaraidani streamchannel were partially revealed through the observation of flows and channel variations on thestream by the TV camera. The mechanism of occurrence and behavior of debris flow were ana-lyzed by the variation of river bed, and the water balance of debris flows in Ashiaraidani experi-mental watershed (6.5 km2).

Step-pool bed forms are common in steep slope streams. In the authors' former paper, a criterion has been presented to predict the occurrence of step-pool bed forms as well asthese geometric features in experimental flumes. The present study will discuss the applica-bility of theoretical, experimental results obtained from basic studies.Field surveys for stream geometry, bed materials, histories of flood flow discharges andso on were carried out at two reaches in mountain region of Jintsu river. The results ofdata-analysies are presented for wave lengths and heights of step-pool systems, bed materialsand flood flows. Then, it is discussed whether the methods having been obtained from basicstudies could or could not predict the field data of the occurrence, mean wave lengths andheights.

The study of runoff process, sediment yield and transport have been performedsince 1966 in the Ashiaraidani creek (7.2 km2) of the Jintsu river.In this study, three problems are discussed;(1) The relation between sediment yield and rainfall, slope grade are examined, to clarify the processes of sediment yield in various slopes, taking seasonalvariations as well as site conditions into accounts. (2) The relation betweensediment runoff and sediment storage in the steep channel with pools wereinvestigated in the Hirudani creek (0.85 km2). (3) The occurrence of debris flow wereinvestigated with attention forcused on rainfall intensity and infiltration in theShiramizudani creek (2.1 km2).

Along the middle course of the Gainata River basin, there exists a belt of the acidicintrusive rocks extending from NNE to SSW. This best is measured as thick as about500 in, and it is consisted of granite-porphyry.In order to consider the morphological characters of the land slope including themechanical character of rocks, some statistical diagrams such as the orientation of jont andland surface, size of joint net, compressive strength of rock and yearly variation of sizeof land slide slopes are proposed.It was found that the orientation of the dip and strike of the land surface is closelyrelated to those of crack and joint of rocks constituting the surface, and that the size ofjoint net is also related to the mechanical character of granite-porphyry in the landsurface.

We extend our investigations of relationship between the composition of water and the orderof weathered rocks which we have mentioned in our previous paper.In this paper, we describe a relation between characters of ground waters and weathering ofrocks.Our investigation is from August 1969 to January 1970, ground water samples were taken atintervals of two weeks. On the other hand, we tried a few experiments on the effect of the consis-tency of water composition on the weathered rocks.Temperature, pH and conductivity values were measured in the field. Chemical constituentssuch as Na+, K+, Ca2++Mg2+ and soluble Si02 were determined in the laboratory.The main results are the following two:(1) The concentrations of Ca2++Mg2+ increased in the landslid areas after small rainfall.(2) The grade of weathered rock is roughly proportional to ionic concentration in groundwaters within the limits of this soluble experiment for rocks.

The authors carried Out some observation on the runoff, sediment yield and transport in asmall mountain watershed, called the Hirudani Experimental Watershed, which is a tributary ofthe Jintsu River in Gifu Prefecture, Japan. This paper presents some results of the observationson soil characteristics, runoff characteristics, rate of sedieent yield and transport, and changesin water qualities during floods. By using these results, the authors consider the relation betweenthe runoff characteristics and the sediment yield and transport in a mountain bsain.

In this paper, the authors discussed the relationship between the landslide and topographical, geological conditions in the Gamada and the Hirayu river basin, by taking three factors as follows;1) Relief energy, which may be a index for the topographical conditions, 2) Conductance(Characters of waters), which may be a index for the geological conditions, and 3) The volumeof landslide material, which expresses the history of landslide.

On the Gainata river basin in Gifu Pref., central Japan, there are various kinds of rapidldnd slide and mud flow. In order to make clear the genetic mechanism of the landslide, it is necessary to observe the geologic structure of the basin such as arrangementof rocks and deposits.It was classified from the authors' observation that geology and geologic structure inthis basin, are made of both the older basement rocks consisted of Paleozoic involvingMesozoic igneous rocks and the young Quaternary deposits consisted of volcanic materialand delluvial and sedimentary deposits.In this area, the main geologic structure in the basement rocks is characterized bythe Circuin Hida tectonic zone, which was made of complex of metamorphic and plutonicrocks, and developed duaring the period from the formation of pre-Cainbrian schist tothe post Mesozoic igneous activity.It was also presumed, on the other hand, that the gigantic mass, the so-calledNohi-rhyolite mass was active in the late Mesozoic along oblique trend to the preexistingwas tectonic zone.The young deposit in the Quaternary is classified as the volcanic materials in theYakedake volcano, located in the Norikura-volcanic zone, and the terrace deposits inPeistocene epock. In this area, these terrace deposits are formed by erosion of preexistingstrata.

Preliminary attempts to research into the characters of landslide in acidic intrusiverocks, have already been described (Yano etc.).The present investigation is essentially an exploration of this idea. The purpose ofthe present investigaion is to examine the relation between weathering of rocks andlandslide. It is the intention of this paper to point out that the relation between thecompressive strength and the density of joint net in these rocks is a clue elucidate practicalorder of weathering.For the research of those characters of weathering in the rocks, the authers measuredthe compressive strength, the density of joint net and analyzed the clay mineral in therocks.The results are summarized as follows: The order of weathering (Capacity of landslide)was decided by the expanse of compressive strength and density of joint net in the graniticrocks.

The authors carried out some observations on tlse runofl sediment yield and transport ina small mountain watershed, called Hirudani Experimental Watershed, which is a tributary of theJintsu River in Gifu Prefecture, Japan. This paper presents some results of the observations onrunoff characteristics, rate of sediment yield and transport on each classification of rocks in thesediment and transport, and changes in water qualities during floods. By using these results, the authors consider as follows:-1) The conductance of flood water is an indicator of the component of runoff.2) The quantity of sediment yields and transport discharge are limited during the period ofthe observed runoff.3) The characteristics of transport materials reflect the runoff processes over the sedimentsource areas.

We extend our investigations of characters of rocks for primary factor of landslide which wehave mentioned in our previous paper.In the investigation of landslide, it is the purpose of this paper to point out that the coherenceof rocks was expressed by weathering of rocks and alternation of rocks for the factor of landslide.In this type of investigation, the choice of the method is in itself a problem, we describethe procedure of survey for the determination of rock coherence and indication method of rockcoherence.We express the extent of rock coherence by the density of joint and the compressive strengh(hammer rebound).

Along the Gamata River basin, there exists numerous landslide. Knowledge of con-ditions under the landslide area is both useful and important for understanding the mechanismof the occurrence of the landslide in this area.For investigation of geochemical features in this area, the authors determined thedistribution and the change with time in the chemical composition of ground waters.This is, from August 1968 to November 1968, ground water Samples were taken at intervalsof two weeks and the composition was determined.Temperature, pH and conductivity values were measured in the field and chemicalconstituents such as Na+, K+, Ca2+ + Mg2+ and Soluble Si02 were determined in thelaboratory.It was found that general tendencies were as follows:(1) The concentrations of Soluble Si02 increased after a rainy term.(2) The concentrations of Ca2+ + Mg2+ decreased after a rainy term.(3) The reverse relation of concentration was observed between the soluble Si02and the Ca2+ + Mg2+. (4) The variation of the concentrations of Ca2+ + Mg2+ and Soluble Si02 in aftera rainy term, were large in the landslide area.