Laboratory Studies of Scour between Overfall Dams in a Curved Channel

I 緒言 II 実験装置及び方法 III 実験結果 IV 考察 V摘要内脛1.0m外經1.5mの圓形水路内に90°を隔てて設置した二つの模型溢流えん堤間に5l/s及び10l/sの流量を流した時に生ずる洗掘の状況を上流堤の軸の向きを種々に変えて調査した。何れの場合にも、上流堤軸が水路の曲率中心え向つている場合は、凹岸の一部に特に深い洗掘を生ずる。但し流量の少い場合の方が洗掘は上流堤に近い位置に出來る。上流堤の軸を凹岸端が下流に近づくむきに回轄すると、凹岸部の洗掘深は速かに減少し、かつ侵蝕の深さは凹岸全長にわたつて、かなり均一化するが、回転角が大になると、洗掘は再び増加する。凹岸部洗掘が最も小さい時の回輔角は10l/sの場合15°、5l/sの場合5°であつた。5l/sの場合には20°附近で下流堤の背後凹岸に接した部分に著しい洗掘が認められた。Two model overfall dams were placed at an angular distance of 90° apart in a circular channel of the inner radius 1.0 m and the outer radius 1.5 m. Using two discharge rates 5 l/s and 10 l/s and varying the direction of axis of the upstream dam, observations were made of the changes in the channel-bed conformation. With either rate of discharge, a severe localized scour occurred at a particular spot under the concave bank, when the damaxis was placed in the direction of the centre of curvature of the channel, the deepest spot being located further upstream in the case of the less discharge. As the axis was so rotated that the concave-bank end turned downstream, the scour diminished rapidly, the eroded depth along the outer bank becoming sensibly uniform. It increased again, however, with a further rotation of the axis. The optimum angle of rotation for the axis of the upstream dam, when scour was the slightest, was ascertained to be about 15° for the discharge 10 l/s and about 5° for 5 l/s. With the latter rate of discharge, an appreciable scour was observed back of the downstream dam in close proximity to the outer bank, when the axis of the upper dam was inclined some twenty degrees to the initial direction