水利工程对长江荆南三口水系结构变化的影响

利用1954、1975、1990、2008和2016年5期长江荆南三口水系图进行解译,并运用灰色关联度模型定量评价区内外水利工程对水系结构变化的影响。结果表明：① 近60 多年来,荆南三口在水系结构一般特征上,河流数量由264条缩减为132条,河流长度由2 183.6 km缩短为1 560.6 km,河频率与水面率分别由0.084条/km ²、17.45%减小为0.042条/km ²、14.33%;在水系结构发育特征上,河网密度、面积长度比和河网发育系数由1954年的0.687 km/km ²、3.96 km/km ²、6.902,依次减小为2016年的0.475 km/km ²、3.17 km/km ²、4.165;从分形特征上看,三口水系4个河区的分维数都在1.5~2.0之间波动,但均呈下降趋势。这表明随着水利工程的不断建设,荆南三口水系自然发育过程受到严重干扰;② 水系结构特征变化受水库总库容影响最大,内部水利工程次之,外部水利工程影响最小,各项指标的灰色关联度均大于0.5。其中,区外水利工程与河频率、水面率、河网密度、河网发育系数、分形维数的灰色关联度分别为0.571 8、0.592 2、0.585 8、0.577 1、0.634 0;区内水利工程数量与各项指标的灰色关联度分别为0.632 5、0.652 7、0.646 5、0.630 6、0.693 7;水库总库容与各项指标的灰色关联度依次为0.707 0、0.729 4、0.722 6、0.712 7和0.728 4。③ 水利工程对水系结构的影响在不同时段呈现出不同的状态,在不同时期水利工程相继运行的叠加影响下,水系受到水利工程影响逐渐增大,水系结构逐步呈现简化趋势。

Effect of Hydrological Projects on River Network Structure in the Three Outlets of Southern Jingjiang River

To study the effect of hydrological projects on the river network structure in the three outlets of Southern Jingjiang River, this article interpreted maps of river network of the year 1954, 1975, 1990, 2008 and 2016, and quantitatively evaluated the effect of projects on variation in river network with the help of grey correlation model. Results show that: 1) In the last 60 years, in terms of the general features, the number and length of river decreased from 264 to 132 and 2 183.6 to 1 560.6 km respectively; River density and water surface ratio reduced from 0.084 per km ² to 0.042 per km ² and 17.45% to 14.33%. In terms of growing features, drainage density, ratio of area to length, and growth index were decreased from 0.687 km/km ², 3.96 km/km ², and 6.902 in 1954 to 0.475 km/km ², 3.17 km/km ², and 4.165 in 2016; fractal dimension of the four rivers in the three outlets, though ranged between 1.5 and 2.0, all demonstrated a declining trend. These indicate that natural evolution of river network in the three outlets of Southern Jingjiang River has been significantly disturbed by construction of hydrological projects. 2) The first important factor responsible for the change of river network is the total capacity of reservoirs, followed by inside projects and outside projects. Factors’ grey coefficients were all above 0.5. The coefficient of outside projects to river density, water surface ratio, drainage density, ratio of area to length, and growth index was 0.571 8, 0.592 2, 0.5858, 0.577 1, and 0.634 0, respectively, while the value of inside projects and total capacity of reservoirs to these indicators were 0.6325, 0.652 7, 0.6465, 0.6306, and 0.693 7, 0.707 0, 0.729 4, 0.722 6, 0.712 7, and 0.7284. 3) The effects of hydrological projects on river network structure were of different characteristics in different periods. Because of the superimposed effect induced by successive operating projects, the influence of hydrological projects on river network has been enlarged, causing simplified structure of river network. Results of this research will play a significant role in the distribution of hydrological projects, channel improvement, and river-lake connectivity projects in both the upper reaches of Yangtze River and the three outlets of Southern Jingjiang River.