城市化背景下河湖水系连通的时空变化及其洪涝响应研究

Aiming at the aggravation of flood disaster caused by river-lake systems connectivity change under the background of rapid urbanization, this project focuses on the action mechanism of the following relation chain, “urbanization → connectivity change → flood response”, and analyze the flood response mechanism of Gulin city. In this study, RS, GIS, mathematical statistics, spatial analysis, numerical simulation, and scenario analysis are adopted, and Guilin is taken as study area because of dramatic river-lake systems change, huge amount of gate dam, and serious flood disaster. Firstly, the evaluation indicator system of river-lake systems connectivity is developed, and the connectivity difference under various spatial-temporal scales is analyzed, to reveal the spatial-temporal change characteristic of connectivity under the background of rapid urbanization. Secondly, based on the methods of complex network analysis and functional connectivity impact assessment, the impacts of river-lake utilization and hydraulic project construction on connectivity are analyzed, and the main driving factors and their influence mechanism of connectivity change are then illuminated. Finally, on the basis of the statistical analysis of flood characteristics, flood process is simulated in a typical urban small drainage, and the flood characteristics are analyzed in the scenarios of floods with different return period and connectivity pattern, then the response regularity of flood to connectivity change is discussed. The controlling countermeasures concerning river-lake systems connectivity is proposed based on the analysis mentioned above. The result of the project is expected to provide scientific basis for the river-lake systems planning, flood control and disaster reduction in Guilin, and at the same time enrich the theory and method of river-lake systems connectivity theory to some extent.

针对快速城市化背景下河湖水系连通变化引起的洪涝灾害加剧问题，拟以水系变化显著、闸坝数量众多、洪涝灾害严重的桂林为例，综合运用RS与GIS技术、以及数理统计、空间分析、数值模拟和情景分析等方法，探讨“城市化→水系连通变化→洪涝响应”这一关系链的作用机制。首先，通过建立水系连通评价指标体系，分析不同时空尺度和连通类型的连通状况，揭示快速城市化背景下水系连通的时空变化特征。其次，基于复杂网络分析和功能连通影响评价方法，分析河湖开发利用与水利工程建设对水系连通的影响，阐明水系连通变化的主要驱动因素及其作用机制。最后，在统计分析研究区洪涝特征的基础上，通过对典型城市小流域进行洪涝情景模拟，分析不同重现期洪水与水系连通状况下洪涝特征的差异，揭示洪涝对水系连通变化的响应规律，提出水系连通优化调控对策。研究成果可为桂林的水系规划与防洪减灾工作提供科学依据，并将在一定程度上丰富水系连通相关研究的理论与方法。

针对快速城市化背景下河湖水系连通变化引起的洪涝灾害加剧问题，以水系变化剧烈、闸坝数量庞大、洪涝灾害严重的太湖平原为例，综合运用RS与GIS技术、以及数理统计、空间分析、数值模拟和情景分析等方法，探讨了“城市化→水系连通变化→洪涝响应”这一关系链的作用机制。结果表明：⑴1991-2015年，太湖平原的城镇用地增加了410.31%，水田减少了57.58%。杭嘉湖区的城镇用地面积扩张速度最快，阳澄淀泖区次之，而武澄锡虞区较慢一些。大城市的城镇用地面积增加幅度相对平缓，而周边中小城市城镇用地面积增加幅度相对较高；⑵1960-2012年，太湖平原河网水系的平均纵向功能连通指数（LFCI）的年代、年份和季节变化均呈微幅上升趋势，但1978年后LFCI的年平均增幅明显增大。洪水期6、7、8月的平均LFCI小于其他月份。平均LFCI的时空变化在水利分区和站点片区尺度上表现出较大的差异；⑶近50年来，苏南平原干流河网的实际成环率、线点率和网络连接度分别增加了8.82%、3.59%和3.57%。在江阴市，支流河网的退化对整个水系的结构连通降低起着决定性的作用，而干流河网的重建不足以抵消支流河网退化所带来的负面影响。在张家港三干河，当闸坝建设在高等级河道时河网的迁移连续性（MC）更小，且随着闸坝数量的增加，MC的最大值和最小值均呈现出逐渐下降的趋势，即闸坝建设对功能连通的影响具有梯度效应和累积效应；⑷在常州运北防洪大包围，连通度为0.4835的1980s骨干河网水系的洪水过程峰值水位均高于连通度为0.4897的2010s骨干河网，连通性更好的2010s骨干河网洪水过程的峰值水位下降了0.02-0.11m，高水位历时下降1-3小时，表明了连通性越好的骨干河网，对洪水过程的调节作用则越为理想。同时，量级越大的暴雨导致洪水过程的峰值水位越高，峰现时间提前，且高水位历时时间更长。另外，河网水系连通变化对洪水过程的影响可能在小量级暴雨事件下更为显著。研究成果为太湖平原的水系规划与防洪减灾工作提供了科学依据，并在一定程度上丰富了水系连通相关研究的理论与方法。