江苏里下河平原城镇化背景下河网水系变化特征分析

Change of river system in the Lixiahe region during urbanization

城镇化等人类活动影响下众多河流水系的破坏,使得江苏里下河平原水安全及生态环境压力加大。基于遥感和地理信息技术方法,以盐城市区为例,开展近30年来水系结构时空变化及城镇化影响研究,结果表明:(1)区域下垫面变化以城镇面积的增加,水田和水体的减少为主要特征,城镇化率由1980年的3.4%增长到2014年的20.8%,2000年后城镇扩张明显加快,呈现从中心老城区以空间蔓延形态向东和向南的趋势;(2)水系变化以低等级水系数量特征减少为主要趋势,其中河网密度和水面率的变化强度和空间差异性最为显著;水系减少使得河网复杂性和区域调蓄能力有所降低,但河网结构整体上仍呈现自然顺直型网状特征。(3)2000年以后城镇面积扩张取代农业活动和水利工程等因素成为水系变化的主要驱动因子,水系变化强度的空间差异增强,城镇化率低于30%的区域,水系变化程度与城镇化线性关系显著;水系特征指标中河网密度、水面率和盒维数对表征该区域的水系数量和结构特征变化具有较好的指示意义,可作为评价水系变化的主要因子。相关研究成果可丰富平原区水系变化案例研究,同时可为该区域未来城镇发展下的水系功能规划及保护提供依据。

The change of underlying surface and river system and its impact on hydrological process is one of the hot topics in hydrological studies especially in plain areas.In this study,we chose the Lixiahe district as the study area,and adopted RS and GIS technologies to study the changes in underlying surface and river system.The results showed that there was a significant change in land use during the urbanization of the study area.The proportion of urban area increased from 3.4% in 1980 to20.8%in 2014,while the area of paddy fields and water body decreased.The urban expansion evidently accelerated after 2000,and showed an eastward and southward tendency from the city center.Drainage density and water surface ratio both declined during the past 30 years.As a result,the structural complexity and the regional regulation and storage capacity of the river system also declined.The change of the river system was mainly characterized by the reduction in low-grade rivers.Urbanization became the main driver in river system change after 2000.The degree of river system change had a significant linear relationship with urbanization in areas with an urbanization rate below 30%.The drainage density,water surface ratio,and box dimension were effective indicators of the quantitative and structural changes of the river system.The research results may enrich the case studies on river system change in plain areas,and provide basis for the functional planning and protection of the river system in this region in the future urbanization process.