| Connecting river and lake system is an effective measure to optimize the strategic allocation of water resources, to raise water conservancy support capabilities, to improve the ecological environment and promote water ecological civilization construction. The Ministry of Water Resources had put river connectivity to be a national strategy. Thus, developing river and lake connectivity patterns in different regions of different levels has important practical significance.Relying on special fund of MWR "Improving Yangtze River Network Structure and River-lake System Connectivity (201201072)," based on the high river density, lake of circulation, high development strength, heavy water environment pressure and other environmental characteristics of the area, from the environmental, hydrological, ecological and other cross-view multi-disciplines, the thesis studies connectivity features and functional goals of river network in plain river area, and initially constructs a multi scale evaluation system for plain river network connectivity. From the river level, regional level, and watershed level, the thesis uses Huangpu River, Dianbei region, and Tai Lake basin as examples, to carry out river connectivity empirical researches at different spatial scales, and propose suggestions regulation. The thesis will provide decision supports and references for fulfillment of environmental, ecological and social services and other related functions connected river and lake connectivity.The main findings of the paper are in the following areas:1. Based on the researches about concepts and contents, evaluation methods, and engineering practices of river network connectivity, the thesis resolves features and functional requirements of connectivity in plain tidal river network.(1) River network connectivity regulation in plain tidal river network is based on the main function and target of connectivity, to optimize river system structure, maintain river water flow. Thus, river network connectivity assessment needs to combine the evaluation of connectivity features with objective function evaluation.(2) River network connectivity features in plain tidal river network include two aspects, one is morphology connectivity based on landscape features, and the second is hydraulic connectivity based on the water conservancy project scheduling. In plain river network areas deeply affected by human intervention, hydraulic connectivity is more practical. Therefore, river network connectivity research in plain tidal river network must combine river morphology connectivity with hydraulic connectivity, and from vertical, horizontal, longitude dimensions to reflect the river connectivity features in different scales.(3) The functions and targets of river network connectivity not only include water volume regulation, water quality improvement, biological support and other natural ecological functions, but also include social services of water supply, shipping, fishing, landscape services.2. River network connectivity in plain tidal river network has spatial scale effects. The thesis discusses and builds a multi-scale connectivity assessment system and index system to evaluate characterizations of plain river network system, and emphasizes to discuss the targets and functions of different scales of river network connectivity.(1) River network connectivity has characteristics of hierarchy and scale, and is divided into normal connectivity, periodic connectivity, and temporary connectivity in time scales, and is divided into river scale, region scale, and basin scale in space scales.(2) Based on the spatial scales of river network connectivity, the thesis proposes a multi-scale evaluation system, and initially builds the corresponding feature evaluation index system and function evaluation index system.On the river scale, assessment should focus on the integrity of the river cross-sectional structure and dam blocking feature, emphasize the ecological and social services functional objectives of the river;On the region scale, assessment should focus on the structural integrity of the river network and hydrologic scheduling, emphasize regional water storage and discharge pattern and water quality improvement and the attainment rate of standard of functional regions;On the basin scale, assessment should focus on key and structural rivers of river basin and hydrological dispatch capacity building, emphasize the basin flood regulation and storage, the water quality improvement, the optimal allocation of water resources and the integrated functions.3. Using the typical plain river network Tai Lake Basin area for empirical research, the thesis carries out connectivity case studies in river, regional, and watershed scales, and explores regulative countermeasures different scales.(1) Using Huangpu River as an example to carry out the assessment and put forward regulative countermeasures on river scale. The result shows that compared with 1965, connectivity level of Huangpu River decreased by about 48.8% in nearly 50 years, and middle reaches of the river connectivity reduced most significantly. Dike construction, land development and other human activities impacted river shore area and heavily intervened river morphology connectivity, especially the horizontal dimension of connectivity, and resulted in river corridor habitat fragmentation and landscape services weakened.In order to improve the landscape service function of Huangpu River, the study carried out a public survey to analysis the preferred forms of morphology connectivity of respondents along Huangpu River. The result shows that the public believe riparian area, embankments, water body, and shallow shoals have descent impacts on the landscape services, and they prefer buffered two-retaining bank structure and continuous vegetation cover in riparian area. Therefore, in order to improve the Huangpu River landscape services, it’s better to strengthen the recovery of the morphology structural integrity in the horizontal dimension in regulation, and to carry out ecological restoration and renovation of the river dike sections with natural riparian corridor continuity.(2) Using Dianbei Region as an example to carry out the assessment and put forward regulative countermeasures on regional scale. The result shows that compared with 1965, river network connectivity level of Dianbei Region decreased by about 41.4% in nearly 50 years, indicating that urbanization made the river area, river nodes, drainage density, fractal dimension and other morphology connectivity feature indicators decreased significantly, and poor sluice scheduling facilities made regional water network hydraulic connectivity function decreased, so that the regional channel storage capacity reduced, water exchange poor, regional self-cleaning capacity decreased, and the water quality is difficult reach Class V level.In order to improve water environment quality, based on environmental capacity method, the thesis analyzes the water needs and the feasibility to improve regional water quality through hydro scheduling to enhance hydraulic connectivity. The result shows through reasonable hydraulic water diversion, the quality improvement goals can be achieved. Therefore it recommends to optimize the regulation of river connectivity in water diversion channels, strengthen regional sluice joint scheduling, and improve the degree of hydrological connectivity.(3) Using Tai Lake Basin as an example to carry out the assessment and put forward regulative countermeasures on watershed scale. This article uses mutation test and trend test of water volume and water level, to assess the result of the typical case of the basin-scale river connectivity implementation. The result shows that the water diversion from Yangtze River to Tai Lake significantly increases water volume into Tai Lake and flow connectivity, shortens water changing period of Tai Lake, and improve water quality significantly. It shows that the implementation of hydro scheduling to enhance hydraulic connectivity is an important measure to improve the connectivity pattern of river and lake, and optimize the overall functions of the water resources allocation in watershed scale.Therefore, it recommends to strengthen key channels and the overall basin river network scheduling capacity building, and optimize scheduling strategies, to improve the orderly flow of the water basin and promote the optimal allocation of water resources in river basin. |
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