平原河网地区城市中心区河流水系变化特征

利用1960s,1980s和2009年水系数据,从数量、结构和连通特征方面分别选取采用河网密度、水面率、河网发育系数、河网稳定度、河网连接率和实际结合度这6个指标,对浙江省杭州市中心区近50 a水系变化特征进行了分析。结果表明:(1)研究区除Ⅱ级河道长度和面积在1960s-1980s有小幅度增加外,河道总体长度和面积均呈减少趋势;河网密度和水面率自1960s以来一直呈减小趋势。(2) 1980s较1960sⅡ级河道发育系数增大,Ⅲ级河道发育系数减小。2009年河道发育系数均呈下降趋势,河网稳定性也呈下降趋势。(3) 1960s-1980s河网连接率与实际结合度呈小幅度减小趋势,连通性略有下降;而到2009年,两个指标均有较大幅度下降,河道连通性下降趋势明显。这种水系特征变化会使得流域洪涝风险也随之加大。

River System Change Characteristics of Urban Central Area in Plain River Network Region

Based on river structure data in 1960s, 1980s and 2009, the change characteristics of river structure of urban central area in Hangzhou City of Zhejiang Province nearly 50 years were analyzed with river density, water surface ratio, development coefficient, river network stability, connection rate and practical combination degree from aspects of quantity, structure and connectivity features. Results showed that:(1) The length and area of the whole river network showed a decreasing trend except that in the secondary river in 1960s-1980s had a small increase. River density and water surface ratio showed decreasing trends since 1960s.(2) Compared with 1960s, development coefficient of river network increased in the secondary river and reduced in the tertiary river in 1980s, which decreased in 2009, the river stability also decreased.(3) River connection rate and practical combination degree decreased, which made the river connectivity decrease slightly in 1960s-1980s. While in 2009, the river connection rate and practical combination degree decrease dramatically, the river connectivity also decreased distinctly, which made the flood risk increased simultaneously.