Study on the Unsteady characteristics of Turbulence Structures of Flood Flows

对汛期水流结构、河床形态和泥沙输移规律的观测具有重要意义。在Hii河，在洪水阶段的流表面上的流模式被拍摄的摄像机，这是固定在一个梯子的顶部固定在下游铁路的桥梁垂直，几乎同时，三维河床形态测量回声测深仪连接到一个十字型浮子下游约50米的洪水流量的平均速度。在洪水期间每2或3小时进行一次测量。从1993年到1998年共进行了9次洪水测量，测量了面积约为15m × 15m的表面流速分布。通过将二维互相关方法应用于在短时间内拍摄的两幅图像来计算水面上的速度矢量。利用所得到的速度矢量计算了流速分布、流线、散度分布和涡量分布，并利用图像处理技术得到的数据，研究了洪水过程中沸腾、旋涡运动和有纵轴的平行螺旋流的特征及其随时间的变化规律。研究了沙波的多重结构、沙丘波高和波长的时间变化、沙波速度以及沙丘运动引起的输沙量。利用得到的流深、平均流速和水面比降计算了曼宁糙率系数，发现当沙丘波高达到最大值时曼宁糙率系数最大。

The field observation of flow structure, river bed configurations and sediment transport during aflood stage are very important. In the Hii River, the flow patterns on the flow surface during a flood stage were taken by video camera which was fixed on a top of a ladder fixed vertically at the downstream rail of the bridge, and almost simultaneously, the three-dimensional river-bed configurations were measured by a echo-sounder attached to a cross-type float which traveled downstream about 50 m at the mean velocity of flood flow. The measurements were made every 2 or 3 hours during a flood. 9 flood measurements were made from 1993 to 1998.The measurement of surface velocity distributions were made over the area of about 15m x 15m. Velocity vectors on the water surface were calculated by applying two-dimensional cross-correlation method to two images taken in a short span of time. The velocity distributions, the stream lines, the divergence distributions and the vorticity distributions were calculated by using the obtained velocity vectors.Based on the data obtained by the image processing technique, the characteristics of boils, vortex motions and parallel spiral flows with longitudinal axes and their time variation during a flood were examined, By using the data obtained by the measurements of river bed, the multiple structure of sand waves, the time variation of wave height and wave length of dunes, the velocity of sand waves and the sediment discharge by the movement of dunes were examined. Manning's roughness coefficient were calculated by using the obtained flow depth, mean velocity and water surface slope, and it is found that Manning's roughness coefficient was maximum when the wave height of dunes reached the highest level.