丁坝对改善城市河流水生生物生景多样性的机理研究

Generally, rivers passing through a city are channelized with a regular cross-section because of their reclamation need. As a result, a natural shape of river profiles was lost and the biodiversity of a river system was become worse or even disappeared due to lacking of variant habitats to provide shelters or places to egg or foster their babies of aquatic lives. In addition, some functions of rivers, e.g. the capacity of self-purification, are vanished once a river suffers from water pollutions. However, spur dykes are widely used to improve the navigation conditions of a shallow river because the river channel can be narrowed or deepened with the actions of spur dykes by changing the hydrodynamics and sediment movements.In order to develop a new kind of spur dykes be capable of improve the habitat diversities of channelized city rivers, in this study, we intend to investigate the mechanism of sediment sorting, river bed changing, and the responsive characteristics of aquatic lives to these changes due to the action of spur dykes by means of field survey and laboratory experiment. Furthermore，high accuracy 2D and 3D numerical models based on unstructured FVM method will be developed and then be calibrated and validated by the results obtained from field survey and experiment. With the aid of these numerical models more detailed information on sediment sorting, river bed evolution and etc. can be further investigated with different type of spur dykes under the conditions of different hydrodynamics and sediments. Finally, an effective spur dyke to be able to greatly improve the habitat diversities of channelized city river can be decided. Additionally, a set of theories and fundamental technologies for the protection of city river environments and biodiversity can be achieved more scientifically.

城市河流多数因河道整治而渠化，从而破坏了河流形态的多样性和水生生物的栖息地、产卵场等生景以及岸边的生态系统，降低了河流的自然净化能力。丁坝作为一种河道整治工程，对调整河道的水沙结构和河床形态作用显著。为了开发一种新型的生态丁坝改善城市河流面临的这类问题，本研究拟从全级配泥沙角度出发，通过现场调查和物理模型试验等手段，探索以丁坝为中心的河床泥沙分选机理、河床演变规律和生态系统结构变化与响应关系。再根据这些研究结果，开发高精度的2D和3D非构造网格水动力学模型、全级配沙泥沙运动和丁坝周围泥沙分选规律的数值模拟模型。最后，根据这些研究成果，从科学的角度提出一套解决城市河流生态环境保护、构建河道生态环境多样性的关键技术和理论体系。

城市河流因人口的不断增长、城镇化、防洪等进行渠化和硬化，取用水和排污的不断增加造成了流量减少、河流形态的多样性和水生生物的栖息地、产卵场等生境以及岸边的生态系统严重退化，河流健康、服务功能、自净能力等面临严峻挑战。丁坝作为一种河道整治工程，对调整河道的水沙结构和河床形态作用显著。为了开发一种新型的生态丁坝来改善城市河流面临的问题，本研究根据项目计划书，以野外调查和数值模拟分析为主，以岷江支流府河流经成都市华阳镇螺丝滩三个丁坝所在河段和日本京都市淀川支流木津川丁坝河段为研究对象；开展了：（1）野外实际丁坝工程对泥沙颗粒特性及其环境影响；（2）鱼类栖息地综合评价模型；（3）丁坝周围水动力与河床形态演变；（4）丁坝对水质和鱼类栖息地改善效果和（5）对水生生物栖息地改善效果最佳丁坝等五个方面的研究。获得的主要研究成果有：天然河道丁坝周围泥沙颗粒的总体分布、纵向分布、横向分布以及在坝田内的分布规律；建立了以鲤科鱼类为代表的水生生物生境要素包括水深、流速、基质和水质（以DO和BOD为主）的适宜性指数关系和加权可利用栖息地面积（Weighted Usable Area, WUA）的评价模型；开发了能够模拟水砂和水质输移转化、河床演变的数值模拟模型，利用该模型研究了单丁坝和双丁坝周围的水动力结构、泥沙冲淤、坝头形式对水动力特性的影响和单丁坝和双丁坝作用下河床形态的演变规律；利用栖息地面积评价模型，以府河丁坝河段为研究对象，通过数值模拟获得了不同流量级、不同丁坝组合情况下丁坝对流速、水深、水质等适宜性指数的作用效果以及对鱼类栖息的改善情况；通过对丁坝坝长、淹没与否、丁坝间距、丁坝数量及丁坝布置等进行系统模拟分析，获得淹没丁坝为改善水生生物栖息地效果最佳的生态丁坝这一重要成果，利用该丁坝可以有效增加栖息地面积高达31.9%。