黄河下游复式滩槽连续急弯段水沙输移规律试验研究

Under the effect of the water-sediment conditions and human activities, disasters frequently occur in the continuous sharp bends with compound channel of the lower Yellow River. The dangers such as erosion and deposition, bend bypassing and shoal cutting are still exist in the regulating of curved channel. However, there is less research on the rule of main flow shifting and the cumulative response of sediment circulation. In this study, a typical continuous sharp bends with compound channel in the lower Yellow River is considered as the research object. By using the field investigation, indoor model test and theoretical analysis, the helical flow structure, the flow exchange between channel and shoal, the variety of dynamic axis, sediment transport and bed formation respond are studied to reveal the inner rules of flow-sediment transport in the continuous sharp bends with compound channel of the lower Yellow River. The results of this study will provide theory support for the further understanding of the characteristics of water-sediment movement, bed formation response and the disaster triggering in the continuous sharp bends with compound channel of the lower Yellow River. It will also provide scientific and reasonable basis for the construction and operation of the water-sediment disaster prevent projects in the continuous sharp bends of the lower Yellow River.

黄河下游受水沙条件和人类活动作用，复式滩槽急弯河段冲淤频繁成灾，弯曲河道的凹凸岸线整治工程仍存在重大的岸滩冲淤、切滩撇弯等安全隐患，而当前考虑连续急弯河段的主流摆动冲淤规律及环流输沙累积响应研究较少。本项目以黄河下游典型复式滩槽连续急弯段为研究对象，以水力学及河流动力学理论知识为基础，采用野外调查、室内模型试验及理论分析为手段，突出研究不同水沙组合及不同形态连续急弯复式滩槽的螺旋流结构、滩槽水流交换、动力轴线变化、弯曲段的同岸与异岸输沙及河床冲淤响应规律，系统揭示黄河下游复式滩槽连续急弯段水沙输移内在规律。本研究成果，将为深入掌握黄河下游复式滩槽连续急弯段水沙运动特性、河床响应及其冲淤致灾提供理论支撑，并为黄河下游连续急弯河段水沙灾害工程防治建设与正常运行提供科学合理的依据。

黄河下游受水沙条件和人类活动作用，复式滩槽急弯河段冲淤频繁成灾。本项目以黄河下游典型复式滩槽连续急弯段为研究对象，通过原型观测、室内模型试验及数值模拟等研究手段，突出研究不同水沙组合及不同形态连续急弯复式滩槽的水流结构、滩槽水流交换、河道输沙能力及河床冲淤等规律，得到以下几点主要成果：.（1）从水体力学平衡角度重新修正了传统的水面横比降计算公式，结果表明床面横比降的存在减小了水面横比降。.（2）采用涡量及涡通量作为环流强度指标，定量的分析了环流的分布特征以及沿程变化。采用涡量垂线分布对纵向平均流速进行校正，得到新的纵向平均流速垂线分布公式，能够在一定程度上捕捉到纵向平均流速最大流速出现在近床面附近的情况。.（3）结合双曲正切函数对横断面地形形态进行拟合，并给出了各个系数的意义及取值范围。.（4）探讨了连续弯道对输沙能力的累积效应，主要表现为涨水阶段，弯道平面几何特征θrc/B与输沙能力成负相关，河道淤积；退水阶段，当漫滩流量接近平滩流量时，输沙能力在局部弯道有增大趋势，河道局部冲刷，水流归槽后，θrc/B与输沙能力又恢复为负相关。.（5）2020年洪水演练期间，河势呈现工程靠流位置下挫，靠主流一侧的滩地多有塌滩现象。根据现场实测的滩唇出水高度变化推算观测点断面流量变化过程，得出滩唇出水高度与流量的相关关系。.（6）同一漫滩流量，滩槽水流交换受水位高低的影响。水位越底，流线越弯曲，指向两岸并在滩地上形成不同尺度的环流；水位越高，流线越直，指向下游且更容易形成切滩撇弯趋势。.（7）探讨了研究河段摩阻流速的变化特性。计算表明，研究河段前半部分摩阻流速较小，后半部分摩阻流速较大，说明该河段后半段的落淤也更为严重。摩阻流速的变化受漫滩流量和出口水位的影响。存在一个漫滩流量和出口水位的组合，使整个河段的系统能量最低。