A Design Of The Artificial Reef Based On Flow Field Analysis And A Study On Relevant Principles

The Xiaojiang River watershed is located in the heartland of the Three Gorges area. With the Three Gorges reservoir retaining water, there emerge a water fluctuation zone covering about 48 square kilometers on the bank of the Xiaojiang River and following eco-environmental problems. First, as the wetland ecosystem of the fluctuation zone is in a transitional phrase, the structure of the phytocoenosium in the system becomes simple and its ecological regulation function diminishes. Second, in the aquatic ecosystem of the reservoir, the construction of the hydrophytic habitat is gradually simplified and homogenized, the self-purification of the water decreases, the pollution load in the storage stays at a high level as the economy along the region develops rapidly and the eutrophication in some waters aggravates as a result of water pollutants retention. Under the influence of many factors, the number of catch species is reducing. It is lower than that of other branches of the Three Gorges reservoir, so is the abundance index of endemic fish, the situation of ecological environment protection is serious in Xiaojiang.Therefore, it is of great research significance to carry out habitat improvemen-t and ecological recovery in Xiaojiang River in the Three Gorges reservoir area.The artificial fish reef technology is currently a remediation technology applied in the marine ecological environment. This thesis suggests applying the technology to the rehabilitation of the Xiaojiang River watershed ecology. Before the application, it should be decided whether it is a key technology of ecological rehabilitation. Therefore, theoretical analysis, experiment research and field survey are significant for the application. In experiment research, to evaluate whether the artificial reef can bring ecological benefits means to assess the reef’s flow field effect and physical stability(namely its hydrodynamic characteristics) and the attractive effect for fish. Considering the current ecological environmental situation of the Xiaojiang River watershed, this paper proposes for the first time the application of artificial fish reef technology in the ecological rehabilitation of the watershed. The research includes the design of the artificial reef, the hydrodynamic performance of artificial reef in the hydro-fluctuation belt, its attractive effect for fish, its layout and feasibility analysis of the project. This thesis aims to lay the foundation for the project of “Research and Demonstration of Key Technology for Ecological Rehabilitation in Xiaojiang River Watershed in the Three Gorges Reservoir”.Guided by design principles for the artificial marine reef, this thesis designs three new functional artificial reefs. After analyzing Xiaojiang River’s seasonal variation of water level, this paper suggests placing the reefs on the water fluctuation zone and designs the artificial reef’s horizontal and vertical layouts based on layout principles for artificial reefs in oceans. The thesis takes Fluent, the CFD(computational fluid mechanics) software as a platform, the enemy-avoiding Reef A as the object of study. It performs numerical simulations of hydrodynamic performances of the monomer reef model and the binary reef model composition put on slops in different flow rate. It also analyzes the distribution of pressure and flow field surrounding artificial reefs and acquires the information of the negative pressure zone, back turbulence intensity and its change with speed. Moreover, the thesis researches the attractive effect of indoor reef models on carps and finds that the range of carps in flag section when there are reef models has increased 20% compared with that when there are models. Finally, it conducts a feasibility analysis of the construction of the artificial reef demonstration zone in Hanfeng Lake in the upstream of Xiaojiang River, designs layouts of artificial reef districts and analyzes reefs’ stability. This paper also presents some work prospects of the theoretical and experimental study on the artificial reef technology applied in Xiaojiang River district. It is hoped that the findings serves as the basis and guide for the application of artificial reef technology to habitat improvement and ecological recovery in Xiaojiang River and other branches in the Three Gorges reservoir.