新丰江流域水网结构演变特征分析

An Analysis on the Stream Construction of the Xinfengjiang River Basin

利用新丰江流域1968和2005年2个时期1：5万地形数据提取水系数据，采用Strahler分级法对流域水网进行分级，从水网基本结构特征、水网分枝特征和水网分维特征等方面对比分析流域水网结构演变特征，结合流域土地利用、气象、水文等数据，从自然因素和人为因素角度探讨水网结构时空变化特征和机制。结果表明，新丰江流域水网结构发育基本符合Horton定律和水系发育的一般规律；但受自然因素和人为干扰的共同影响，1968—2005年间，新丰江流域的水网结构也呈现简单化、主干化发展趋势，水网条数、密度、等级、水网分枝能力和水网分维等指标都有不同程度的降低，其中l级水网，尤其是分布在河流源头区和水库周边地区的1级水网变化较大，导致了流域水网等级的降低，最高级水网从1968年的7级降到2005年的6级；对流域水网结构影响较大的是人为因素，主要体现为区域的土地利用变化以及植被的破坏等影响了流域的水网结构，主要是通过直接破坏和对土壤侵蚀的影响来破坏初级水网的发育。

The Xinfengjiang River basin is one of the most important drinking water source in Guangdong Province. In this paper, characteristics of the change of basic stream construction, stream bifurcation, and stream fractal dimension are analyzed by using the data of 1968 and 2005. Combined with land use data, meteorological data, and hydrological data of the basin, the impacts of natural and human factors on spatial evolution of stream construction are discussed. The results show that： （1） during 1968-2005, the river network structure appeared as a trend from comprehension to simplicity. The values of stream number, density, rank, bifurcation, and fractal dimension all decreased to a certain extent. The first rank streams had greater decrease, that made the grade of the river network in the basin reduce from 7 in 1968 to 6 in 2005. The total length of the river network was shortened by 620.35 km, and the number of rivers had a reduction of 818. （2） The ratios of bifurcation in the first and fourth grades of river network reduced, while those in the second and third grades of river network increased. That means the nature bifurcation characteristics of river network were deteriorated. （3） The fractal dimension value decreased from 1.945 to 1.698 during 1968-2005. The value in 2005 was still at normal level, as compared with the fractal dimension values in other regions. （4） There was significant semi-logarithm linear correlation between grade of river network, number of rivers, and mean length of rivers. The correlation coefficient is between 0.977 and 0.998. The results accorded with Horton law and river network length law. （5） The changes of river network in the Xinfengjiang River basin were influenced by the natural factors and human factors. Human factors, such as land-use change and damage of vegetation, did more harm to river network than natural factors did in a short period. It is necessary to adopt some methods to protect this important water source area from adverse influence of intensive human activity.