淹没植被与非淹没植被组合群落对河道水沙运动及冲淤变化的影响研究

Vegetation in natural rivers, wetlands and tidal areas often exists in the form of a combination of both submerged and emergent vegetation. Three-dimensional flows and vortex structures which are linked to sediment motion and bed morphology are more complex behind combined vegetation, compared to the flow patterns behind single emergent or submerged vegetation. Applying the theories of fluid mechanics, mechanics of sediment transport and fluvial processes, the applicants will investigate flow characteristics, vortex structures, flow resistance, sediment motion and fluvial process behind a combined vegetation community. Also, applicants will focus on the interaction of forgoing contents. Through flume experiment and theoretical analysis, the motion and influence area of three vortices produced by vegetation will be separately determined. The variations of flow patterns in longitudinal and lateral directions will be clarified. The key factor controlling sediment motion and bed morphology in vegetated region will be found out. The method for estimating critical initiation velocity within vegetated region will be proposed. The model capable of predicting channel conveyance capability will be presented. The quantitative relation between longitudinal vegetation extension and sediment motion will be elucidated. Those breakthroughs will perfect and update the theory, concept and method relative to the interaction between combined vegetation and the motions of water and sediment. The achievements of this project will enrich the research contents of river dynamics and geomorphology, and will provide the theoretical and technical supports for river restoration, river training, and bank protection by vegetation, etc.

水生植被常以淹没植被与非淹没植被组合群落的形式出现在天然河道、湿地和潮汐地带。组合群落会产生较单一淹没或非淹没植被更为复杂的三维水流及漩涡结构，影响群落区域的水沙运动及河床形态。申请课题以流体力学，泥沙运动力学和河床演变学为基础，研究组合群落区域的水流特性、漩涡结构、泥沙运动和河床演变，及它们之间的相互影响机制。通过水槽试验和理论分析，阐明群落区域水流各项特性在横向和纵向的变化规律；确定组合群落产生的三种漩涡的运动轨迹及作用范围；辨识植被控制泥沙运动和河床冲淤的关键因子，提出植被区泥沙临界起动流速计算方法；阐明非淹没植被纵向扩张与水沙运动和河床演变的定量关系；建立组合群落区域过流能力计算模型；提出随机分布组合群落关键参量改进计算方法。课题将实现组合群落与水沙运动相互作用在理论、概念、机理和方法上的完善和创新。研究成果将丰富河流动力学的研究内容，为河流修复、河道防洪等提供理论支持。

水生植被常见于天然河道与湿地。植被增大局部阻力，改变水流结构，形成复杂漩涡结构，影响水沙运动与河床演变。项目围绕植被影响下的水流结构、漩涡结构、泥沙运动与河床演变，通过水槽试验和理论分析，取得了如下七方面研究成果：1）揭示了滩地有淹没植被漫滩河道中弯曲主河道二次环流沿程分布，提出了弯曲主河道水深平均二维水流流向预测方法；2）揭示了河道中植被群落内部及周围的复杂水流流场，建立了河道有、无植被区水流流速分布解析计算模型；3）探讨了不同植被分布对水流流速与植被拖曳力的影响，发现均匀分布植被能更好的减缓水流冲击，其屏障作用较随机分布植被更突出；4）揭示了不同淹没度下斑块植被尾端漩涡与河床演变规律，越大的植被淹没度能产生越强的水流流速与紊动能，植被淹没度与植被密度是影响河床冲刷的关键要素；5）揭示了不同植被直径对植被产生紊动能与泥沙起动条件的影响，提出了植被区泥沙起动流速预测公式；6）研究了不同植被分布（均匀、随机与群落分布）对河道中推移质输沙率的影响，提出了复杂植被分布下推移质输沙率统一预测方法；7）研究了滩地有植被展宽河道沿程水动力特性与输沙能力变化规律，提出了主河道流量预测方法与泥沙运动状态判别条件。.项目取得的所有实验数据均在已发表论文中说明了数据获取渠道。上述研究成果可为河流与湿地的生境修复、岸滩保护提供理论与技术支撑。