Numerical model of channel evolution like a braided river was constructed in the present study. Slopecollapse model was developed and was appled in the present simulation model so as to keep the local slope angle be equaled to or less than the angle of repose at any time in numerical computation. This model was also also developed so that the effect of emerged bar was able to be treated reasonably. In this paper, the evolution process of braided river was the target of the investigation on the basis of numerical simulation under the condition of Fujita's experiment. The important remark of this study is that the side-bank erosion affects the braided channel formation process in low water channel considerably.

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In order to stably maintain a river channel, the river channel form needs to suit its origin. Therefore, many researches on the origin of the plane form of a river channel or river width have been conducted. However, the relation between a channel network and meandering shape or a sandbar and the formation process of a channel network is not sufficiently clarified. In this research, in order to clarify these phenomena, a hydraulic model experiment using a wide width flume was conducted and the results were discussed using meandering theory and bar formation theory. As a result, it has been shown that the bars and braided channels may be influenced to some extent by the wave resulting from plane instability.

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In this study, we propose a simulating method to predict channel pattern in braided reach. Stream length which is defined as the distance from a channel bifurcating point to next bifurcating point, can be predicted by the channel width and the Froude number of the stream channel. We calculate the channel pattern using the channel length, separating rates of flow discharge and angles of channel bending at bifurcating paints.
The channel pattern calculated by the simulation model agree well with the experimental data. And also, the temporal variation of sediment discharge through braided channels can be estimated by this model.

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　本研究は，前報の非平衡掃流砂運動の役割に続いて，洪水流の三次元性に伴う非平衡浮遊砂運動の河床変動に与える影響を検討している．解析結果から，安倍川下流域では洪水減水期に浮遊砂量が相対的に大きくなり，浮遊砂と掃流砂が砂州上に広く堆積することにより砂州と澪筋との比高差を大きくするとともに，平均河床高の上昇を引き起こすことを考察した．さらに，砂州上の流れと澪筋の流れが混合することで，砂州側縁では二次流が発達し澪筋から砂州に向かう流れが形成されることで，砂州側縁に浮遊砂が顕著に堆積し，砂州の横断方向への移動が生じて澪筋幅が縮小する機構が確認された．しかし，実際に起こっている

の大規模な変動を説明するには至っていないことから，これを説明するための今後の課題をまとめている．

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Decreasing process of bar modes, which was found in basic experiments on plain bed and is regarded as a fundamental characteristic in formative process of multiple bars, is discussed with initial bar amplification of various modes evaluated by an existing linear stability theory. Specific features of multiple bar formation with micro scale bedforms are summarized from experiments carried out on a fine sand bed, where the mode decreasing process was also observed. Validity of the existing stability theory is examined to apply to prediction of changes in multiple bar modes on ripple-covered fine sand beds.

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直線水路において, 平坦初期河床上に給水と給砂を定常的に与える条件で形成される自己形成流路の形成過程と形成水理条件を水路実験と数値解析により検討を行った. その結果, 自己形成流路は複列砂州の発生領域で形成されることが明らかにされた. さらに, 自己形成流路の形成過程では, 複列砂州が発生するが, 時間とともに交互砂州, さらに自己形成流路と変化することが明らかにされた. そこで, 数値解析により平衡状態の複列砂州の再現を試みたが, 全ての計算条件において自己形成流路が形成され, 複列砂州が平衡状態に到達しない条件が広く存在する可能性が示された. さらに, モード (0, 2) の河床形状の発達が, 1本の流路を有する自己形成流路の形成に重要な役割を果たしていることが明らかにされた.

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In braided channels, channels vary spatially and temporally, which results in the big variation of the sediment dischrge. It is important to know the channels pattern and process of stream channels variation. Channel patterns can be predict by the length and width of each stream channel. In this paper, two dimensional simulation model are employed to clarify the process of sand bar formation and channel diverging phenomenon in a gradually widening channel, in order to investigate the length of a stream channel. The results of the calculation are compared with the data obtained from flume tests to verify the numerical model.

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Channel network configurations are changed by hydraulic conditions. The characteristic of a river channel network configuration is directly connected with river channel disasters and a river ecosystem. For this reason, the relation between the form characteristic and the hydraulic conditions needs to be grasped. In this study, hydraulic experiments on channel network configurations were conducted. Sufficiently wide flume was used for the experiments so that the influence of side walls might not appear in the channel network formation. Although few channels were formed in the hydraulic condition that the bed shear stress was near the critical bed shear stress, multi-row bars were formed in the condition that the bed shear stress is to some extent large. As a result of conducting linear stability analysis, it was shown that a phenomenon which is different when hydraulic conditions differ arises.

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The channel deformation in Kinu River during a flood period was investigated in the present study. Field measurement and film analysis were conducted to quantify the temporal and spatial changes in channel profile in the reach of 54.5-56.5 km from the confluence point to Tone River in the term between 2001 and 2003. Considerable amount of bank erosion and channel shift were observed, and the alternative channel was created just after the final flood during this term. As a result of this analysis, it was found that the magnitude of channel deformation depends on an individual flood discharge and also on the history of the former flood events. Numerical analysis was also conducted to understand more deeply the mechanism of this channel deformation. It was confirmed that the numerical model worked fairly well.

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Temporal and spatial variation characteristics of braided streams between straight confining walls are studied by means of flume experiments and numerical simulations. Results are summarized as follows.(1) The number of streams produced in a straight channel depends on the width-depth ratio; the number of streams increases with the width-depth ratio.(2) The geometry of streams shows self-similar characteristics which suggests the possibility that the streams promote restoration of natural riverine ecosystem.(3) Small-scale bed geometry significantly affects the formation of large-scale bed geometry. In addition, stabilization mechanism of bars is discussed focusing on unsteadiness of flow and growth of vegetation. The results suggest that decrease of maximum water discharge promotes bar stabilization.

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　本研究は，石礫を含んだ広い粒度分布の河床材料からなる安倍川

において，洪水流の三次元性に伴う掃流砂，浮遊砂の非平衡土砂移動機構及び洪水中の澪筋の移動等を明らかにすることを目的としている．流れの解析は非静水圧分布を考慮した準三次元解析であるQ3D-FEBS法，掃流砂の運動には，修正長田・福岡モデル，浮遊砂の運動には後藤・福岡モデルを用いた新しい河床変動解析法を適用し，の河床の変形について実測値と比較している．その結果，本解析法が網状河川安倍川の洪水流河床変動解析に有効な手段を与えることを示している．

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　本研究では，水路実験より種子のへの定着特性を把握すると共に，植生分布の違いが流路変動特性に及ぼす影響について検討した．結果，では定常給水条件下であっても流路内の流れが非定常となるため，種子は時空間的に広く分散して定着し，砂州上に縦断方向にライン状の植生パッチを形成した．流路変動に関しては，砂州全面に植生繁茂させた実験では，従来の報告通り流路本数の減少とそれに伴う低水路幅の拡幅，流路の蛇行化が確認された．流路の消失には，流木等の詰まりによる小スケール流路の消失と，二股流路の主流路側への土砂堆積に起因した主流路切り替えに伴う旧主流路消失の2タイプが認められた．一方，の砂州上に植生パッチが形成された実験では，植生は流路本数減少と蛇行化には働かず，むしろ小スケール流路の増加に伴い流路を複雑化させた．これは，で確認されるIsland Braiding現象の維持形成機構の一端を説明するものと考えられる．

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A single strong meandering stream is often observed in double-row bars rivers which attacks river bank and causes local scouring and bank erosion in even medium-size flood.Therefore,to maintain the safety against flood in double-row bars,we need knowledge on mechanism of such formation process and factors which bring about a single strong meandering stream.In this study,a depth-averaged flow and bed-variation analysis is carried out under the regime condition in double-row bars.Results of the simulation show formation of a single strong meandering channel and bank erosion and invasion of excessive vegetation in bars are factors which strengthen such a single meandering stream.

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Dynamic characteristics of braided streams formed on beds with non -uniform sediment are discussed by means of numerical analysis. Results are summarized as follows.(1) Sedime nt particles are exchanged to fine ones in dry bed regions and coarse in streams, respectively, under steady flow conditions, whereas, under unsteady flow conditions, mean diameter in trough increases in the rising stage of water discharge and decreases in the falling stage.(2) If the frequency with which water covers bars decreases by reducing peak flood discharge, vegetation growth will be promoted. Furthermore, vegetation suppresses the development of small streams and grows large streams.(3) If huge amount of sediment is excavated artificially, number of streams will decrease with eroding bed in main streams.

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Channel evolution of braided stream was studied numerically in the present study. Slopecollapse model and modified bedload function were included in the numerical model whose validity had been almost verified. The formation and developing mechanism of each braided channels is the one of the target to be understood physically. The interaction between a bed deformation and a bank erosion in this process is the other main point to be investigated. On the basis of the enormous number of data obtained by the numerical experiments under the different conditions, the important and interesting remarks on the above two points were found and discussed here.

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　洪水時の複列砂州河川の河道被災として，大きな蛇行流路の形成による河岸侵食がその典型的な事例であり，その機構解明は河川管理上重要な課題である．こうした背景のもと著者らの既往研究により，複列砂州の片側河岸砂州が拡大し，これが下流に交互伝播することで単列蛇行流路が形成する過程と，側岸侵食からの供給砂が流路固定，単列蛇行化を促進することを水理実験から見出し，さらに河岸侵食と上流側土砂供給がこの流路形成に影響を与えることを認識した．そこで本研究では，側岸侵食を伴う複列砂州の単列蛇行流路の形成過程に与える土砂供給の影響を，移動床水理実験と平面2次元河床変動解析から検討した．その結果，土砂供給による堆積傾向が単列蛇行流路の発達を促して強調化させることを提示した．

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Forested bars with large relative height between channel bed and bar surface is one of the typical figures in gravel-bed rivers. That causes strong meandering flow and bank erosion in several medium-size floods. In this study, such a morphological feature in gravel-bed rivers with double-row bars is investigated considering interaction between wood land expansion and channel formation process. A depth-averaged flow and bed-variation analysis is carried out introducing the events of invasion and destruction (wash-out) of riparian trees. Result of the simulation shows formation of a single strong meandering channel with fixed bars which can be seen as a resent channel characteristic in double-row bars with vegetation.

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流路は時空間的に複雑に変動するため，個々の流路形状の将来予測は非常に困難である．これは，流路網が様々なスケールの流路によって構成され，小流路の現象が大流路の現象の挙動に影響を与えるためだけでなく，個々の流路内で発生している河床面不安定現象にも起因している．本研究では、流路の不安定性が流路内のどの領域における河床面不安定性の影響を強く受けているかを数値解析により検討した．その結果，浅く早い流れとなる瀬は，深く遅くなる淵に比べて不安定な場を形成していることが明らかになった．さらに，擾乱に対して安定性の強い流路と弱い流路の特徴を明らかにし，数値解析による地形情報の利用方法を提案した．

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Bedforms of a mountain rivers are composed of three different scale undulations of large-, medium-and small-scale unit. In the recent investigations, the origin and the properties have been elucidated on two kind of the the small scale units and one of the medium scale units. However, little knowledge has been obtained on the large-scale unit. For the reproduction of the large-scale bedforms and ofthe superposed three different scale undulations, steep channel experiments with heterogeneous movable bed were conducted under the overlaped hydraulic conditions; at first the formation discharge of dowble row bars was run and continuously the low discharge was run on the previous bed. The experimental results showed that (1) reproduced bedforms in the exprimental channel were very similar to those of the actual moutain river Shiramizu which has three differernt scale undulations on the bed, and (2) large-scale bedform in a mountain river would correspond to multi row bars formed by a large flood to overspread the bailey width.

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