植被河段宽级配泥沙分选造床与河势变迁动力机制研究

Vegetation commonly occurs on banks and sediment bars of mountain ephemeral rivers. Through modifying the flow characteristics, vegetation tends to affect the characteristics of bed sediment sorting and river morphological change as well as pattern transformation. Numerous existing studies have investigated and explored the two-dimensional characteristics of vegetated flows, and sediment transport and river morphological change are based on uniform sediment motion theory. The gained knowledge of hydrodynamics and sediment and river morphological dynamics, however, may not be properly applicable to natural rivers, particularly mountain rivers with wide particle-size distribution. Due to such uncertainty, this research project aims to investigate the three-dimensional hydrodynamics of vegetated rivers, including flow velocity distribution, turbulent characteristics, secondary flow pattern and transfer of momentum and energy. These flow characteristics are expected to have important implications on the understanding of sediment-related characteristics. In addition, bed scour experiments are carried out to investigate sediment sorting, river morphological change and pattern transformation in vegetated rivers. The gained hydrodynamics are generalized and used to develop a three-dimensional turbulence model. The model is employed to simulate the three-dimensional flow structure and pattern rationally and accurately. This research project is expected to overcome the uncertainty that two-dimensional flow structure cannot accurately account for three-dimensional flow behaviors and the associated sediment motion and river morphological processes in real scenarios. The gained hydrodynamics, sediment dynamics, and river dynamics can reveal the intrinsic interaction of flow structure, sediment sorting and river pattern transformation in vegetated rivers. The results can provide significant implications and applications on ecosystem restoration and flood-sediment-related disaster prevention in mountain rivers.

山区季节性河流的河岸、洲滩植被丛生，显著影响植被河段局部水流结构，进而改变了宽级配床沙分选规律及河床冲淤变化与河势变迁。本项目突破前人常用的二维植被水流分析方法和均匀沙试验手段，通过详细测量植被河段三维水流结构（流速分布、紊动特性、二次流形态，动能量交换转移）和宽级配河床冲淤变形与河势变化，结合自主研发的“植被－水流－泥沙”三维数值模拟方法，系统研究含岸边植被的三维水流结构和植被河段宽级配非均匀沙分选与河床冲淤变形规律，从而弥补平面二维水流方法无法探究的植被水流三维垂向结构及泥沙分选和河床变形研究的不足，以揭示植被河段“水流结构－床沙分选－河势变迁”相互作用的内在动力机制。该研究成果对于山区河流植物宽级配河段的生态环境保护和水沙灾害防治具有重要的理论意义和应用实践价值。

山区季节性河流的河岸、洲滩植被丛生，显著影响植被河段局部水流结构，进而改变了宽级配床沙分选规律及河床冲淤变化与河势变迁。本项目突破前人常用的二维植被水流分析方法和均匀沙试验手段，通过详细测量植被河段三维水流结构（流速分布、紊动特性、二次流形态，动能量交换转移）和宽级配河床冲淤变形与河势变化，结合 “植被－水流－泥沙”数值模拟方法，系统研究含岸边植被的三维水流结构和植被河段宽级配非均匀沙分选与河床冲淤变形规律，从而弥补平面二维水流方法无法探究的植被水流三维垂向结构及泥沙分选和河床变形研究的不足，揭示了植被河段“水流结构－床沙分选－河势变迁”相互作用的内在动力机制。经过三年的实施，依据研究计划、研究主要内容、研究目标等，顺利完成了项目，并取得了良好的研究成果。受本项目资助，以一作/通讯共发表了10篇高水平学术论文，其中SCI论文8篇、EI论文2篇，包括Water Resources Research, Journal of Hydrology, Catena, Hydrological Processes等顶级期刊，撰写了2项发明专利。本项目研究成果对于山区河流植物宽级配河段的生态环境保护和水沙灾害防治具有重要的理论意义和应用实践价值。