弯曲复式河槽与滩地植被对高含沙漫滩水流运动的耦合作用

Hyperconcentrated over-bank floods are affected by vegetation of floodplains and geomorphology of compound meandering channels. Flow and sediment exchange between main channel with floodplain and deposition distribution are extremely complex, which have an important influence on formation and development of secondary suspended river, adjustment of transverse gradient and evolution of flood control situation. The project takes compound meandering channel of the Lower Yellow River as research object. Based on a series of generalized model experiments of hyperconcentrated overbank floods in compound meandering channel with vegetated floodplains, the lateral distribution regularities of water and sand movement are presented; physical figure of water and sediment transportation is established; coupled impacts of compound meandering channel and vegetation on hyperconcentrated flow movement are revealed. On this basis, the mechanism model of the lateral distribution regularities of water and sand movement during hyperconcentrated over-bank floods in compound meandering channel with vegetated floodplains is established, which has clear physical figure and physical mechanism. And then base on quantitative calculation and contrast analysis under a variety of combinations of river boundary and water and sediment, the influencing mechanism of hyperconcentrated over-bank floods in compound meandering channel with vegetated floodplains on erosion and deposition of main channel and floodplain is uncovered; the influence of patch forest and long-stalked crops in the Lower Yellow River on morphological development of transverse section such as transverse gradient is illuminated. This project not only has important practical significance for governance management of floodplain area of the Lower Yellow River Yellow River and management of the secondary suspended river, but also has important scientific significance for promoting multi-disciplinary integration of hydraulics, river dynamics and ecology.

高含沙漫滩洪水受滩地植被和弯曲复式河道形态的影响，滩槽水沙交换和淤积分布规律非常复杂，对二级悬河的形成与发育和滩面横比降的调整乃至防洪形势的演变作用显著。本项目拟以黄河下游弯曲复式河槽为研究对象，通过系列滩地植被作用下弯曲复式河槽高含沙水流概化模型试验，凝练弯道滩地植被作用下高含沙水流水沙横向分布规律，构建弯曲复式河槽和滩地植被耦合作用下高含沙洪水水沙输移的物理图形，揭示其耦合作用机理；在此基础上，建立基于清晰物理图形与物理机制的弯曲复式河槽滩地植被作用下高含沙水沙横向分布的理论模型；并开展多种河道边界与水沙组合下的定量计算和对比分析，揭示弯曲复式河道滩地植被及其分布对高含沙水流滩槽冲淤的影响机制，阐明黄河下游片林和高秆作物对滩唇淤积和滩面横比降等横断面形态发育调整的影响。该项目不仅对黄河下游滩区和二级悬河治理具有重要的实际意义，而且对促进水力学、河流动力学与生态学融合具有重要的科学意义。

高含沙漫滩洪水与滩地植被和弯曲河道的影响交织在一起，导致水沙分布和流动结构非常复杂，直接影响滩槽水沙交换和淤积分布，对二级悬河的形成与发育和滩面横比降的调整作用显著。.项目开展了弯曲复式河槽与滩地植被对高含沙漫滩水流水沙输移的耦合作用机理，弯曲复式河槽与滩地植被耦合作用下高含沙漫滩水流水沙因子横向分布理论模型，弯曲复式河槽与植被耦合作用下高含沙水流对滩槽冲淤调整的影响三方面的研究内容。结果表明：.1）通过不同滩地植被布置情形下弯曲复式河槽的系列模型试验，分析各工况下水沙横向分布及其发展变化规律，建立了弯曲复式河槽滩地植被作用下高含沙漫滩洪水水流泥沙因子运移的物理图形。①流速横向分布沿程变化：上段变化较大，而下段相对均匀；②滩地植被对水流流速的减缓作用明显；③滩地种满植被布置对滩地流速及淤积分布都有均匀作用，可减小堤脚附近流速过大现象以及增大主槽流速作用。.2）在动量方程中加入植被拖曳力项，结合弯道水力学理论，建立基于清晰物理图形的滩地植被弯曲复式河槽高含沙水流流速和挟沙力横向分布理论模型，通过五个算例对提出的分布模型进行检验，对比分析模型计算结果与试验数据符合较好。.3）定量分析滩地植被对滩槽冲淤调整的影响，揭示了弯道滩地不同植被及其分布作用下高含沙漫滩洪水对滩槽冲淤调整的影响机制。①由于滩地淤积主要在滩唇部分，导致主流不仅仅在主槽内，还可能出现在左右岸大堤堤脚附近，形成顺堤行洪；②滩地无植被情况下，主槽容易出现移动；③两岸植被不管是一排还是种满植被，都对主槽稳定有作用。阐明黄河下游片林、高秆作物对滩唇淤积和滩面横比降等横断面形态发育调整的作用。.项目开展了系列的滩地植被弯曲复式河槽高含沙漫滩水流概化模型试验，获得了包括流速、含沙量、河床冲淤状况等关键数据。.项目不仅对黄河下游滩区和二级悬河治理具有重要的实际意义，而且对促进水力学、河流动力学与生态学融合具有重要的科学意义。