近50年长三角地区水系时空变化及其驱动机制

Temporal and spatial change of stream structure in Yangtze River Delta and its driving forces during 1960s-2010s

基于1960s、1980s以及2010s三期1:5万地形图中水系数据,选取河网密度(Dd)、水面率(WSR)、干流面积长度比(R)、支流发育系数(K)和盒维数(D),探讨了长江三角洲地区水系近50年的时空格局及变化特征,并分析了城市化对水系结构的影响。结果表明:1近50年来,长三角水系河网密度、水面率数量特征呈下降趋势,其中武澄锡虞、杭嘉湖和鄞东南地区河网密度减少近20%;结构特征发生变化,秦淮河流域干流面积长度比增加显著,杭嘉湖地区支流发育系数衰减达46.8%;河网复杂度衰退,武澄锡虞和杭嘉湖地区的盒维数衰减分别达7.8%和6.5%。2城市化影响水系的空间分布,高度城市化地区河网密度、水面率、支流发育系数以及盒维数最低。3城市化深刻改变着水系的演化过程。1960s-2010s期间,高度城市化地区的河网密度、水面率衰减剧烈达27.2%和19.3%,河网主干化趋势加剧,河网复杂度下降4.91%。1980s-2010s期间,低度城市化地区支流衰减达53.3%,河网密度大幅下降14.6%。4城镇用地的扩张、水利工程的修建和农田水利活动是改变长三角水系的主要方式。

Spatial and temporal variations of river systems in the Yangtze River Delta（YRD）during the 1960s-2010 s were investigated based on streams derived from the topographic map in the 1960 s, 1980 s and 2010 s. A list of indices, drainage density（Dd）, water surface ratio（WSR）, the ratio of area to length of main river（R）, evolution coefficient of branch river（K）and box dimension（D）, were classified into three types（quantitative, structural, and complex indices） and used to quantify the variation of stream structure. Results showed that：（1）quantitative indices（Dd, WSR） presented a decreasing trend in the past 50 years, and Dd in Wuchengxiyu, Hangjiahu and Yindongnan decreased by about 20%. Structurally, the Qinhuai river basin was characterized by a significantly upward R, and K value in Hangjiahu went down dramatically by 46.8% during the 1960s- 2010 s. A decreasing tendency in D was found to dominate the YRD, and decreasing magnitude in Wuchengxiyu and Hangjiahu peaked for7.8%, and 6.5%, respectively in the YRD.（2） Urbanization affected the spatial pattern of river system, and areas with a high level of urbanization exhibited least Dd（2.18 km/km2）, WSR（6.52%）, K（2.64） and D（1.42）, compared with moderate and low levels of urbanization.（3）Urbanization also affected the evolution of stream system. In the past 50 years, areas with high level of urbanization showed a compelling decreasing tendency in quantitative（27.2% and19.3%） and complex indices（4.9%） and trend of enlargement of main rivers（4.5% and 7.9% in periods of the 1960s- 1980 s and 1980s- 2010s）.（4） Expanding of urban land, construction of hydraulic engineering and irrigation and water conservancy activities were the main means.