複断面蛇行開水路流れの構造と低水路の河床形態に関する研究(2)

Abstract

流れが高水敷に及ぶ洪水時の流れを対象に、低水路を移動床とした複断面蛇行水路において、2次流構造とそこに形成される河床形状との関係を、流れの可視化結果および速度計測結果を用いて検討している。対象とした流れは, 直線水路内に設置した低水路の蛇行度SI(=蛇行長/蛇行波長)が1.llと1.38の2種類の複断面流れである。両者の水路において, 基本単位と考えられるらせん状の2次流構造は同様であるが, 生成される数が異なる.その結果, 河床に形成される洗掘域・堆積域の列数も異なっている。

Over-bank flow in a straight channel with sinuous/meandering main channel is discussed based on experimental results. The experiment was carried out in a compound sinuous/meandering channel with movable main channel. Bed form measurements, velocity measurements and flow visualization in a cross section were conducted. The results indicate that there exists a certain relationship between the secondary flow and eroded and deposited regions on the bed. Two types of secondary flow were observed, one is the spiral motion induced by the shear stress between main channel and flood plain flows, and the other can be observed at the downstream side of the ridge in the deposited region. The separation of main channel flow behind the crest of sand bar produces this latter one.