长江下荆江段分形学特征与河道演化

Fractal Characteristics and Watercourse Evolution of the Lower Jingjiang Segment in Middle Yangtze River

采用盒数维法对长江下荆江各不同时期河道岸线的分形学特征进行探讨。研究表明,下荆江河道岸线的盒数维介于1.078~1.23之间,较黄河、海河、滦河等河流的维数要小,相当于黄河下游和长江下游平原区的维数,反映出下荆江河段是高成熟度的河段。这与长江中游地区的其他河段不相称,可能是由江汉—洞庭湖平原长期沉降所造成。河道裁弯之后,河道岸线由复杂变简单,分维数显著减少。裁弯取直事件发生在分维数值为1.19~1.23之间,即分维数可作为河道突变事件发生的一个预警参数。

The fractal characteristics were discussed according to the fractal analysis of segments in lower Jingjiang River in this paper.The parameter of dimensions are changing between 1.078 to 1.23 and are lower than those of Yellow River,Haihe River and Luanhe River and close to those of plain areas in lower Yellow reaches and upper Yangtze reaches.The result indicates the evolution of segment is mature period,which is disproportional to other segments of this catchment.This is maybe controlled by its geological settings,especially long-term slow subsidence of Jianghan-Dongting Lake plain.After the watercourse is cut off,the fractal value decreases evidently associated with the simplification of watercourse.The curve cut-off of segment generally occurs between 1.19 and 1.23 of dimension.Thus the fractal value can be regarded as an early warning parameter.