城市化对福州市河网演变特征的影响

Influence of Urbanization on River Network Evolution in Fuzhou City

探索城市化下河网结构的演变,为未来城市规划建设提供参考。以福州市城区为例,基于2005年1月与2019年12月高精度卫星影像和遥感数据等资料,运用图论法,研究2005年以来福州市城区河网演变以及城市化响应。结果表明:(1)2005-2020年,福州市城镇化率从54.5%增长到72.5%,河网形态演变剧烈,各项水系结构指标呈衰减趋势,水面率、河网密度和河流密度分别减少了17.93%、16.81%和20.06%;河网结构空间差异明显,城市中心的井字型人工河道河网结构参数整体变化较小;建成区边缘的自然形态河流发生了较大改变,灌溉河渠在城市建设中消失;(2)研究区内河流整体连通性呈现正向增长,过去15年间河流数量减少使节点数和河链数均减少20%,但连通性指标有不同程度上升,人类活动在干扰河流正常发育的同时,也构建出较为科学的河网形态,河网连通性在城市成熟阶段得到一定的改善;(3)城市化水平与河网演变存在相关性,其中建成区面积对河网结构与连通性影响较大。5个研究区中,建成区面积与河流密度呈现极显著相关(P<0.01),与河网密度呈现显著相关(P<0.05)。

With the acceleration of urbanization,the problems of urban land shortage and landscape frag-mentation have become more severe.Therefore,it is important to explore the evolution of river network structure for urban planning and construction.In this research,five districts in Fuzhou City were selected for case study,and we studied the evolution of the river network and urbanization of Fuzhou City from 2005 to 2020 using graph theory.Information was obtained from high-precision satellite images and remote sensing data collected in January 2005 and December 2019.Land use in the study area was divided into four types:forest,water,urban and farmland.Results show that:(1)The urbanization rate of Fuzhou City has increased from 54.5%in 2005 to 72.5%in 2020.During this period,the river morphology of Fuzhou city changed dramatically,and all river structure indices trended downward.The water surface ratio of the five districts in Fuzhou declined from 8.20%in 2005 to 6.73%in 2020 and the river network density dropped from 0.90 to 0.75,while the river frequency dropped from 0.33 to 0.26,with dramatic decreases of 17.93%,16.81%and 20.06%,respectively.From the perspective of river morphology,river curvature has decreased,and the water system has gradually become more networked.The spatial difference in river network structure was obvious,and the overall change in the well-shaped artificial rivers in the urban center was small,while the natural river form at the edge of the built-up area have changed greatly.Paddy fields and irrigation canals have disappeared within the urban construction.(2)The overall river connectivity in the study area grew and,while human activities disturbed normal river development,they also built a more scientific river network morphology and river network connectivity improved.(3)There was a correlation between the level of urbanization and river network evolution,and the built-up area influenced river network structure and connectivity.In the five study areas,the built-up area was signifi-cantly correlated with river frequency(P<0.01),and with river network density(P<0.05).