蜿蜒河道水沙结构调整与水生生物栖息地响应机理研究

River health and its ecological restoration are the main problems confronted in China, especially a series of ecological and environmental problems caused by straightening, channeling, hardening and discharging a lot of pollutants. Meandering or bending is becoming a new trend and new methods of ecological restoration of urban rivers. Meandering rivers will have secondary flow and transverse slopes due to the action of gravity and inertial centrifugal force. The structures of river flow and sediment will be changed accordingly and resulted in a phenomena of erosion at the concave bank and deposition at the convex bank. From a standpoint of habitats diversity of aquatic live, the formation of convex bars is relatively simple. How to make full use of the river meandering to reach a goal of protecting the stability of concave bank at one hand, and creating diversity of aquatic habitats and improving the water quality at another hand. Therefore, spur dikes installed at the both sides of bending river banks are proposed and following studies will be carried out in this study: (1) evaluation method to improve the aquatic habitats; (2) effects of scour control by the layout of groins at concave bank; (3) effectiveness of improving an relative simple sandbar and habitat diversity at the concave bank by spur dikes and; (4) Habitat improvement effect under the joint influence of spur dikes at both sides of meandering river banks. Finally, an optimal layout scheme of spur dike group to improve the habitat diversity of aquatic life in the meandering river will be put forward according to the research results. Furthermore, this study can also provide a set of important technologies and theoretical support for the ecological restoration of municipal rivers.

河流健康及其生态恢复是我国河流面临的主要问题，尤其是城市河流经截弯取直渠化、硬化和大量排污造成的一系列生态环境问题。河道蜿蜒化或弯曲化正成为城市河流生态恢复的一种新趋势和新方法。弯曲河道水流在重力和惯性离心力作用下会产生二次环流及断面横比降，从而导致河流的水沙结构发生变化，形成凹岸冲刷、凸岸淤积，从水生生物生境多样性考虑，凸岸形成的沙洲相对比较单一。如何充分利用河道的蜿蜒化来达到既能保护凹岸稳定又能创造出水生生物生境的多样性和改善河流水质？为此，本研究提出在蜿蜒河道两岸布置丁坝群方案开展研究：（1）水生生物生境改善效果评价方法；（2）凹岸布置丁坝群的防冲效果；（3）凸岸丁坝群布置形式对单一沙洲及生境多样性的改善效果；（4）两岸丁坝群共同作用下的生境改善效果。最后，根据研究结果科学合理地提出对改善蜿蜒河道水生生物生境多样性效果最佳的丁坝群布置方案，为城市河道生态修复提供一套关键技术和理论支撑

城市河流的健康及其生态修复是我国河流面临的主要问题，河道蜿蜒化正成为城市河流生态修复的新趋势，弯道水流在重力和惯性离心力作用下会产生二次环流及横比降，从而导致河流的水沙结构发生变化，形成凹岸冲刷、凸岸淤积。从水生生物生境多样性考虑，凸岸形成的沙洲相对比较单一。如何充分利用河道的蜿蜒化达到既能保护凹岸稳定又能创造出生境的多样性是当前值得深入探讨的问题。为此，本项目的主要开展了以下研究：（1）通过构建3D RNG κ-ε数值模型，VOF处理自由面，以180°弯曲水槽实验数据为基础，重点进行了水动力和形状参数对弯道二次流的影响。（2）利用Google Earth分别对长江上游、中游和下游典型河段进行了统计分析，得出90°为最具代表性的蜿蜒型河道，以此为典型探讨了弯曲河道两岸分别布置不同丁坝群方案对水生生物栖息地的改善作用。（3）以岷江支流锦江穿过成都市华阳的弯曲河道为研究对象，开展了在实际河道中对概化90°蜿蜒河道丁坝群布设方案的有效性验证。（4）针对常用的IFIM法使用加权可利用面积的栖息地评价结果仅能代表栖息地可用面积的数量，不能反映其质量及功能斑块属性等问题，基于拓扑和随机游走理论，探讨了洄游鱼类产卵场生境评价理论研究。获得的重要成果有：（1）弯道二次环流中的最大流速分布，主涡（Main Center Cell）、凹岸次涡(Out Bank Cell)和分离流的形成机制及其与形态参数和水动力影响因素之间的关系。（2）在概化90°蜿蜒河道的凹岸布设非淹没、凸岸布设淹没式丁坝群对河势稳定和生境质量的改善效果最佳。（3）在成都市锦江华阳弯曲河道的实例中进一步验证了概化90°蜿蜒河道中丁坝群布设方案的有效性，其布设方式不仅能保护凹岸不被冲刷，还能在凸岸营造出浅滩、深潭交错的丰富栖息地生境，对长期河道生态健康十分有利。（4）提出了基于拓扑和随机游走的产卵生境评价新理论，研究小尺度功能连通性对鱼类产卵过程的影响机制。这些研究成果可为城市河流系统健康与生态功能恢复提供一定的理论支撑。