Hydraulic characteristics and bed deformation on embayment and mid flood plain in compound open channels

本文通过试验研究了复式明渠消沙区的三维水流结构和泥沙淤积。本文选取消力池形状、消力池底床相对高度和丁坝的存在作为设计项目，利用PIV技术研究了它们对消力池区水流结构的影响。在同一水槽中进行了泥沙淤积试验，考虑了水流结构与泥沙输移过程的关系，并以底床与主槽底床的相对高度为控制参数。在无漫滩流的情况下，在消能区产生单一的垂向涡。在漫滩流情况下，横向涡与垂直涡在消落区共存。在矩形边界层情况下，随着边界层深度的增加，横向涡的纵向尺度相对于垂直涡的纵向尺度变大 ...更多信息 腔结果，床附近的流动模式变得彼此非常不同，这影响了沙沉积的量和形状。在梯形湍流中，斜阶跃产生倾斜的横向涡。这种涡的纵向尺度变得比矩形情况下的小，这产生不同于正常的台阶情况下的流动模式。其次，研究了河漫滩、中漫滩和主槽三断面河漫滩带的水流结构和悬沙输移规律。在三断面河槽中，横向动量交换加速了河漫滩的流速，进而增加了河漫滩的输沙率。河床相对高程对泥沙淤积速率影响很大。当悬移质床面与主槽床面相同时，推移质和悬移质由主槽输往悬移质。当河槽床面高于主槽床面时，漫滩泥沙由河槽向主槽输送。这些特征与消落带的三维水流结构密切相关，消落带的植被阻止了主槽的入流，并改变了下游消落带的再附着长度。这种效应使得沙沉积比没有植被的情况下更平坦。少

We investigated three-dimensional flow structures and sand deposition in an concavity zone in a compound open channel experimentally. We picked up the concavity shape, the relative level of concavity bed and the existence of spur dikes as design items and investigated their effects on the flow structures in concavity zones by using PIV method. Furthermore, sediment deposition tests was conducted in the same laboratory flume and the relation of flow structures to sediment transport process was considered.The relative level of the concavity bed against the main channel bed was considered as a control parameter. A single vertical vortex is generated in a concavity zone in the case without overbank flow. In the case with overbank flow on flood plain, a transverse vortex coexists with the vertical vortex in the concavity zone. In rectangular concavity case, the longitudinal scale of the transverse vortex becomes larger relative to the vertical vortex with an increase of the depth of the con … More cavity. As a result, the flow pattern near the bed becomes very different from each other and this affects the amount and the shape of sand deposition. In trapezoidal concavity, skew step produces inclined transverse vortex. The longitudinal scale of this vortex becomes smaller than that in the rectangular case and this generates different flow patterns from the normal step case. Consequently, overbank flow causes transverse vortices in the concavity zone and then changes flow structures and sand deposition shape.Next, we investigated flow structures and suspended sediment transport in concavity zone on triple section channel with flood plain, mid-level flood plain and main channel. In the triple section channel, transverse momentum exchange accelerates the velocity and then increases sediment transport rate on the flood plain. The sediment deposition rate in the concavity is much affected by the relative bed level. When the bed level of the concavity is the same as the main-channel bed, the bed load and the suspended load are transported from the main channel into the concavity. When the bed level of the concavity is higher than the main-channel bed, the flood-plain sediment load is transported from the concavity to the main channel. These features are well related to the 3-d flow structures in the concavity zones.The vegetation in concavity zone prevents inflow from the main channel and changes reattachment length in down step zone. This effects makes sand deposition flatter than in the case without vegetation. Less