近50年杭—嘉—湖平原水系时空变化

Temporal and spatial changes of river systems in Hangzhou-Jiaxing-Huzhou Plain during 1960s-2000s

基于1960s、1980s和2000s地形图水系数据，采用河网密度、水面率、河网发育系数、干流面积长度比和盒维数等指标，对杭嘉湖地区近50年水系空间分布和时间演化进行了研究。结果表明：（1）杭嘉湖地区1960s．2000s期间水系长度和面积呈衰减趋势。近50年河流长度减少了11023．33km，衰减了38．67％，水面积减小了151．58km^2，衰减了18．83％，且这种趋势在加剧；r2）支流发育系数呈下降的趋势，河网随着城市化的发展逐渐主干化。1960s二级支流发育系数为1-41，至1980s下降到1-35，下降了3．9％；1980s．2000s期间急剧下降至0．15，下降了88．6％；（3）水系变化的空间差异明显，河网密集的南部区水系衰减最为剧烈；（4）在不同下垫面条件下水系变化有各自特点。城市区水面率较小，约4．9％～9．4％，1960s以来水面率、河网密度呈减小的趋势，伴随城市化过程出现较重要的城市防洪疏浚、新挖河道工程。河网区河网密集，约2．1—5-3kin／km2，支流下降明显，干流有增加趋势以致河网主干化。典型湖区水面率较大，约17．8％～19．7％，水系格局变化相对不明显。

Based on the topographic map data in 1960s, 1980s and 2000s, the temporal and spatial changes of river networks of Hangzhou-Jiaxing-Huzhou Plain region were analyzed from aspects of the river density （DR）, rate of water area （Wp）, development coefficient of the fiver network （Kw）, the ratio of area-length of main fiver （RAL） and box dimension （Do） etc. The results showed that： （1） DR and Wp presented a decline trend during the 1960s-2000s with fiver length decreased by 11023.33 km （about 38.67%） and water area decreased by 151.58 km2 （about 18.83%）, and the trend was still intensifying. （2） Ko also showed a decline trend with K2 decreasing from 1.41 to 1.35 （a decrease of 3.9%） during the 1960s-1980s and to 0.15 during the period of 1980s-2000s （decreased by 88.6%）. And the main rivers were gradually dominant in river network in the process of urbanization. （3） The spatial variation of the river network was obvious, the southern regions with an intensive river network was the most dramatic. （4） Each river system has its characteristics under different underlying surface conditions. Wp was smaller with 4.9%-9.4% in city regions. The DR and Wp had decreased since the 1960s. Some river channel projects for dredging and urban flood control were implemented in the process of urbanization. In the regions of intensive river network （DR was 2.1-5.3 km/km2）, there was a significantly decreasing trend of tributary rivers, and an increasing trend of main rivers. In the lake regions with bigger Wp （about 17.8%-19.7%）, there were no significant changes of river system pattern.