基于物理生境构建的多交界面箱式丁坝水沙特性研究

In the modern river ecological project, groyne is able to support an abundant habitat for aquatic life, which is available for minimizing the river degradation and benefits the river restoration. A box groyne is an integrated unit composed by various types of single groyne and the internal environment surrounded by single groynes, and it satisfies the different requirements of river ecology. The characteristics of interface between box groyne zone and main stream (as size, position et al.) affect the exchange process of water, materials, momentum and energy between the groyne ecosystem and main environment. The configurations of box groyne need to ensure that it has enough ability to maintain a healthy, vigorous and sustainable environment for aquatic life. On that premise, the promotion of box groyne on river restoration is clearly presented by creating the environment with abundant flow structure and sediment transportation. Hence, the exploration of box groyne with different configurations of multi-interface on the characteristics of hydrodynamics, erosion and deposition of sediment is meaningful, and it benefits the construction of river physical habitat and provides the scientific basis on ecological promotion to the engineering design and construction of these hydraulic structures. In contrast to the widely applications of the box groyne in river engineering, less information about the box groyne under special shaped in river is available. Under the construction of river physical habitat, the present study mainly aims at the box groyne with different configurations of multi-interface. The comprehensive studies of box groyne with multi-interface on the three-dimensional characteristics of flow field, the mechanism of sediment transportation is developed by the experiments of physical model and numerical simulation, and the method to estimate the exchange coefficient is improved for multi-circulation system and diversified interfaces. The study of this project supports the design and evaluation of box groyne on river restoration, and contributes to the research of groyne hydraulics.

丁坝引起的强烈三维紊动水流可在河流中创造出多样化的水体和地形环境，为水生生物提供适宜的生息空间。箱式丁坝是基于双丁坝及其包围的内部区域，可辅于顺坝组成的一个综合单元体，其与外界水体环境的交界面属性（如尺寸、位置等）直接影响丁坝生态系统与外界的水体物质交换。在保证箱式丁坝内水体环境健康的前提下，通过优化配置多种交界面来构造丰富的水流流态和泥沙冲淤环境，可构建多样化的物理生境以促进河流生态恢复。因此，深入研究箱式丁坝的水动力学、泥沙特性对交界面变化的响应机制和规律，对有效预测其构建物理生境的表现有重要意义，并为其生态优化设计提供科学依据。本研究以构建河流物理生境出发，通过物理模型和数值模拟实验相结合的手段，探讨多交界面下箱式丁坝的三维流场、河床局部变形等特性，对其水体交换系数估算方法进行改进。从科学的角度为箱式丁坝应用在河流生态恢复上提供设计评价的理论依据和技术支撑，并可丰富丁坝水力学研究。

丁坝是一种被广泛用于河岸防护、航道整治的河流水工建筑物，但同时对局部流场和地形环境的改善，可有利于水生生物栖息地建设。为有效降低坝头冲深及丰富丁坝周边水流地形结构，本项目在传统双实体丁坝的上游丁坝上设置一个横向交界面（缺口），形成多交界面箱式丁坝，通过合理优化交界面参数在保证坝内水体健康前提下，构建多样化物理生境以促进河流生态恢复。本项目采用物理模型实验和数值模拟实验相结合的方法，考虑不同缺占比LN/L（横向交界面中心与丁坝中心重合，横向交界面长度与丁坝长的比值）、缺偏比LNP/0.5L（横向交界面中心距河岸长度与0.5倍坝长的比值）、阻水率HG/h（横向交界面底坎高度与水深的比值）的横向交界面参数，对缺口单丁坝、多交界面箱式丁坝附近水力特性、局部冲淤特性及水体交换特性的影响规律进行探讨，并基于河流生态修复角度给出一定工程建议，研究成果简要归纳如下：.（1）对于单丁坝和箱式丁坝，横向交界面皆有利于坝后流场、地形的多样性发展，尤其是多个垂直剪切混合层的存在，促进水体交换并增加水流结构的丰富性，上升流的存在有利于底质中营养物质进入水体，这些都有利于水生物栖息地环境构建。值得注意的是，对于多交界面箱式丁坝，最大冲刷深度由原来坝头位置移到横向交界面的远岸侧。.（2）缺占比的增加有效促进水体交换和降低坝头冲刷，当横向交界面尺寸较大时，缺偏比对过水体交换能力无较大影响，但要注意横向交界面过于靠近堤岸侧时，水流的偏转将影响堤岸安全。横向交界面设置较低底坎（阻水率小于0.3）带来的水平剪切混合层和过水断面压缩不仅能丰富水流结构降低坝头冲刷，更能强化坝内水体交换过程。.（3）基于河流物理生境恢复的多交界面箱式丁坝工程设计中，缺占比不宜大于0.33、缺偏比不宜低于0.4、缺口阻水率不宜大于0.5，并综合考虑水体交换能力适中的工况配置，才能在有效保护丁坝自身和堤防安全前提下，保持一定回溯环流区尺度并制造局部深潭和浅滩为水生生物提供所需的栖息地环境。