Flow characteristics in open channel vary by the change of boundary conditions like discharge, channel geometry, roughness, slope, downstream depth and so on. Therefore sustainable development in design of hydraulic structures depends on comprehensive understanding of flow phenomena. Flow phenomena in pool-and-weir fishway, at its downstream vicinity, upstream connecting part, submerged states and hydraulic jump were studied. Three dimensional flow structures in oscillating jump was also studied. The results were gathered below.

　　Flow characteristics at downstream vicinity of stepped-weir channel is important to design its energy dissipator. Experiments were conducted both in sloping and stepped-weir channel of slope of 1/10. Pool length, pool depth and shape of weir were varied at stepped-weir sloping part. It is revealed for the same discharge that tail water depth of jump that was occurred at the toe of stepped-weir channel is smaller than that was occurred at the toe of sloping channel. It indicated that the height of wing wall of stilling basin would de smaller in stepped-weir channel.

　　The toe length from end weir, entrance and tail water depth of jump that was occurred at the toe of stepped-weir channel were analyzed according to Rand's(1955) empirical equations. A non-dimensional parameter as Drop number according to Rand (1955) is used. The relationship between Drop number and ratio of entrance depth and weir height was corresponded well with Rand's expression. Similarly the relationship between Drop number and ratio of tail water and weir height was also agreed well for all boundary conditions. Hence, a new range of D≧0.001 adaptable to Rand's empirical equations was obtained. Moreover, when the Drop number was plotted against the ratio of toe length and weir height, it is observed that toe length in stepped-weir case is smaller than vertical drop. This relation indicated that the length of stilling basin would be shorter in stepped-weir channel.

　　The sand protection dam (Sabo dam) has been developed for aquatic lives by installing full width pool-and-weir fishway. The energy dissipator is one of the major problem in this fishway, inasmuch as, its design is still adopting as smooth sloping channel which is bigger than appropriate size for fishway. To solve the above problem experiments were conducted with varying geometry of fishway, changing appurtenance at upstream & downstream connecting part, slope and discharge.

　　The basic findings are expressed herein about design of energy dissipator of full width pool-and-weir fishway to encounter flood flow.

　　By changing downstream connecting part shape, hydraulic characteristics of toe depth and so on with slope of fishway and various connecting part shape were indicated which would show the clear direction of design in a certain range.

　　The observed and calculated values of toe depth and so on were compared. Here, calculated values of toe depth are obtained by using observed downstream depth of jump and Froude number at that section. It was confirmed that both values corresponded well.

　　The relation by upstream condition downstream connecting part with slope of fishway and so on was investigated. Eventually, characteristics of boundary point and its depth, before beginning of uniform water surface flow, were become clear and related expression were derived with I and W. This result would be useful to indicate minimum length of fishway.

　　Finally, the Manning's n value of about uniform flow varied with slope of fishway, and related expression was developed to design.

　　Tumbling flow in pool-and-weir fishway was investigated to observe its behaviour, range and originating place. It is revealed from experiments that this flow varied with pool length and discharge. This flow appears in shorter pool length with smaller discharge and longer pool length with bigger discharge. In present experimental range the upper and lower limit of the flow were indicated by empirical equation. Itoriginates at the uppermost pool of the fishway periodically and flows downward like wave surge. The height of wave varies with pool length and discharge. Recurrence interval is small in shorter pool length and which is high in longer pool length. These findings would be useful to design side wall of the fishway.

　　Submerged flow in pool-and-weir fishway is appeared when the tail water depth is increased. Experiments were conducted to verify flow condition if tail water depth was increased. It is revealed that three sub-regimes like breaking wave, surface wave and surface jet are emerged in submerged regime which are quite similar those were occurred in submerged weir and submerged vertical drop. There is no significant change of flow condition both at upstream and downstream due to its increasing and decreasing trend of tail water depth. The submerged regime of flow in pool-and- weir fishway were expressed empirically. The experimental results are stretched the information to design above fishway.

　　Hydraulic jump is occurred if the tail water depth is raised during flood flow in pool-and-weir fishway. Hydraulic jump in this fishway may be treated as jump in large scale roughness channel. Three dimensional velocity distribution would be very much useful to understand the flow phenomena in side the jump. It is revealed that maximum velocity (Um ) path is shifted to upper layer immediately after jump. It is occurred probably due to strike of entrance jet at the bottom weir and which results the direction of flow upward. A reverse direction of flow is also observed after certain distance from entrance of jump which is again disappeared after a limited distance downward. The velocity decay of forward flow is higher than wall jet. According to experimental results, forward flow is symmetric but not uniform. The flow velocity along the center line is lower than nearby side wall which indicates the "climb" effect. The traverse(v) and vertical component (w) of flow are stronger at beginning part of jump which are decreased downward gradually. Experimental data showed that the jump flow in pool-and-weir fishway is three dimensional in nature. It is believed that these results would useful in computation of jump flow as well as further research development in sloping roughness channel. In this research the basic hydraulic characteristics were become clear under various hydraulic conditions which indicated the new direction of design. From now, flow characteristics at spot were reconfirmed and we could use an appropriate hydraulic design by using this research result.

　　The hydraulic jump of low range Froude number is usually encountered in irrigation channel, head works, low head weir, dam and so on. It is already established that oscillating jump of low range Froude number is some extend dangerous in horizontal channel. Inasmuch as, it produces large wave with no periodicity but this wave production is diminished when the tail water depth is increased. For same range of Froude number tail water depth of jump in sloping channel is higher than classical jump. Experiments on oscillating hydraulic jump were conducted in sloping channel. Three dimensional velocity distribution in side the jump were recorded. Experimental data showed that entrance jet oscillates at very beginning of the jump and this oscillating jet diffuses early due to high tail water depth. As a result, although an eddy is formed at any side of the channel but no damaging wave is observed. This eddy also influences the decay of high velocity jet. Thus it may be inferred that sloping stilling basin for low range Froude number is recommendable. It is observed that velocity decay is high from the beginning of the jump than wall jet. Data of velocity distribution clearly indicated that the flow in oscillating jump in sloping channel is three dimensional in nature.

　開水路における流況特性は、流量、水路形状、粗度、勾配、下流水深などの諸条件によって異なる。

　本研究は、水路全幅型階段式魚道工の流れを対象に、魚道工の下流付近、上流接続部、潜り越流時と跳水時の水理現象を調べ、また、揺動跳水時における３次元的流れ構造を調べて、水理設計に向けての各々の水理条件下における基本的な水理特性を明らかにせんとしたものである。

　研究成果は、次のようである。

１．下流付近での流況特性

　階段式水路の下流付近の流況特性の把握は、エネルギー減勢工を設計するために重要である。実験は１／10勾配の水路と階段式水路の両方で行われた。その結果、同一流量時においても、階段式水路のテイシ（ toe）で生じさせた跳水時の下流水深値は勾配水路のテイシで生じさせた下流水深値より小さいことがわかった。これより、階段式水路における静水池深さは浅くてよいことになる。Randによる無次元パラメータの落下指数Ｄを用いて、末端堰からのテイシ長、階段式水路のテイシで生じさせた跳水時の流入水深と共役水深を検討した。その結果、Ｄと流入水深と堰高の比の関係は、Rand式によく一致し、また、下流水深についても同様であった。ここで、従来のRand式に比べて、Ｄ≧0.001の新たな適用範囲が求められた。

２．エネルギー減勢工

　砂防ダム等では全幅型の階段式魚道工を取り付けることにより、水生生物に対しての改善の取り組みがなされ始めている。しかし、その設計法はいまだに平らな勾配水路として取り扱っており、的確な魚道工サイズよりも大きく、課題のひとつである。この課題を解決すべく、魚道形状、上・下流の接続部形状、水路勾配、実験流量を変えて実験を行った。ここでは、出水時を対象として全幅型階段式魚道工におけるエネルギー減勢工の基本的な知見を得んとした。結果は次のようである。

　下流水路の接続部形状を変えることによって、魚道工勾配と種々の接続形状に伴うテイシ水深などの水理特性を調べ、関係式を求めた。なお、テイシ水深などの観測値と計算値を比較したところ、両者の値はほぼ一致した。次に、魚道工勾配などに伴う下流接続部に対する上流条件についての関係を調べた。その結果、等流水面の始まりの境界位置とその水深の特性が明らかになり、勾配と魚道始端堰高に伴う関係式を示した。最後に、ほぼ等流時のマニングのｎ値は魚道工勾配に伴って変化し、関係式を求めた。

３．撹乱流と潜り越流

　階段式魚道における撹乱流の挙動、発生範囲とその位置を調べた。この撹乱流の発生はプール長と流量によって変化した。そして、この流れが発生する上・下限の関係式を求めた。撹乱流は魚道工の最上流プールで定期的に発生し波動を呈して下方に流下する。波高はプール長と流量に伴って変化することを示した。

　潜り越流の実験は下流水深を増加したときの流況を明らかにするためになされた。潜り越流では砕波、表面波、表面ジェットの３つの越流形態が現れ、関係パラメータを用いて水理特性を示した。

４．跳水

　階段式魚道工において出水時に下流水深が上昇すると斜面上に跳水が発生する。魚道工における跳水は大型粗度水路の跳水として取り扱われよう。３次元の流速分布測定は跳水内の現象を調べるのに有効で、最大流速は跳水後すぐに上方にシフトすることがわかった。底部に流入ジェットが衝突し流れの方向が上方になるためである。センターラインに沿っての流速値は"はい上がり"効果として示され、側壁付近よりも低かった。

５．斜面上における揺動跳水

　低フルード時の跳水は潅?水路、頭首工、低い堰、ダムなどで出会う流れである。低フルード数時の水平水路における揺動跳水は危険であることは既に確立している。つまり、無定期的に大きな波をつくり、この波の生産は下流水深が増加すると弱まる。低フルード数の斜面上の跳水時の下流水深は規範的跳水時よりも高い。揺動跳水に関する実験を斜面上で行い、３次元流速分布を記録した。その結果、跳水の先端では流入ジェットが揺動し、この揺動するジェットが下流水深が高いために早く拡散することがわかった。結果として、水路側で渦が形成されたけれど、無害な波の観測となった。渦は高流速ジェットの減衰に影響を及ぼす。