Impact of urbanization on stream structure and connectivity of plain river network in the Taihu Basin

太湖流域的快速城市化使河流形态发生了改变，影响了平原河网水系结构与连通性.本文以近几年城市化发展较为迅速的张家港地区为例，基于景观生态学和图论的相关理论，利用2002与2015年的水系数据，对全区以及各行政分区水面率、河网密度、河频率等指标进行研究，旨在揭示该地区河网水系结构与连通性参数变化及城市化对其影响.结果表明：研究区2015年与2002年相比全区各水系结构指标都呈减小趋势，水面率、河网密度、河频率的衰减率分别为15.7%、12.6%、33.3%，河网有主干化趋势，干流面积与长度发育的同步性较好；不同行政区的水系变化有明显的空间分异，张家港南部水系较北部水面率、河频率衰减更剧烈；东北部地区河网密度与河网复杂度变化明显；张家港全区河网连通性略有提高，但地区分异明显，沿江的西北部地区河网连通能力有所加强，而东南部内河区域河网畅通程度减弱，被圩区、水闸与泵站切断的水系需要更合理的调度方案才能增强并维持水体的连通度；水面率、河网密度与人口、GDP之间相关水平较高，各地区水系结构参数与其变化率的空间分异和该地区人口、经济发展水平密切相关；河网河链数、节点数受城市化影响较大，线点率、实际连通度的变化与城市化指标相关性较弱.本研究可以为后期张家港地区优化水系结构及防洪排涝建设提供基础，并帮助基于各片区的特点开展因地制宜的管理.;The rapid urbanization of Taihu Basin has changed the river morphology and affected their structure and connectivity. In order to reveal the change of stream structure, connectivity and the impact from urbanization, Zhangjiagang region, which has developed rapidly in recent years, was selected for research. Based on the related theories of landscape ecology and map theory, the water surface rate, river network density, river frequency and other indicators of the whole region and administrative regions were studied using the data of 2002 and 2015. Results show that:(1) The structural indexes of river network showed decreasing trends. The attenuation rates of water surface rate, river network density and river frequency were 15.7%, 12.6% and 33.3%, respectively. The river network was getting simpler, while the area and length development of main stream were synchronous. The change of river system in different districts varied spatially. The attenuation of water surface rate and river frequency in the south of Zhangjiagang were more severe than that in the north. The density and complexity of river network changed obviously in the northeast region. (2) The connectivity of river network in whole region was slightly improved with significant difference among regions. The connecting capacity of the river network in the northwest area along Yangtze River has been strengthened, while the unimpeded degree in the southeast area was weakened. The river systems cut off by polders, sluices and pumping stations need more rational scheduling schemes to enhance and maintain the connectivity of water. (3) The correlation between water surface rate, river network density, population and GDP were relatively high, and the spatial difference between the structural parameters of river system and its change rate in various regions was closely related to the population and economic development. (4) The number of river chains and nodes in river network were greatly affected by urbanization. The change of line point rate and actual connectivity were weakly correlated with urbanization indicators. This study can provide a foundation for the optimization of river network system structure, flood control, drainage construction, and help to develop management according to local conditions based on the characteristics of each area in Zhangjiagang.