游荡性河流演变规律研究进展及其河型归属探讨

Progress on the study of fluvial process of wandering rivers and discussion about its channel pattern classification

游荡性河道在中国广泛分布,其中以黄河下游上段最为典型,但关于游荡性河型的归属问题尚存在很大争议,国际上多将游荡性河流归属为辫状河型。本文以黄河下游游荡性河道为典型案例,系统总结了游荡性河流的演变特征、主要影响因素和形成机理,并从定义、成因、特征及河道形成过程方面,将游荡与辫状河型的异同点进行对比分析。得到以下启示:游荡性河型是一种重要的河道型态,与辫状河型在许多方面存在较明显差异。特别是游荡河型主要发育于能量小于输沙需求的环境,因而形态呈现不稳定特性,但辫状河型不仅出现在能量较多的环境,而且也常在能量较小的环境中出现,因而一部分具有稳定形态,另一部分则表现出不稳定的特性,因此,有必要对游荡性河道和辫状河道给予区分。最后对未来研究进行了展望,提出应重视河型形成的内在机理,对能量理论进行发展及深化,进一步系统性评价游荡性河道与辫状河道的异同性,以解决游荡性河道的河型归属问题。

Wandering rivers frequently occur in China, especially in northern China, with the wandering reach of the lower Yellow River as the most typical case. However, controversy concerning their channel pattern classification remains. While such rivers are widely regarded as wandering or wandering-braided channel in China, they are categorized as braiding rivers largely by the international geomorphological community. In this article, the wandering reach of the lower Yellow River is taken as an example and the evolutionary characteristics of channel morphology is summarized, focusing on the factors influenced the channel evolution in different periods. Based on the summary, a comparison is made between braiding and wandering rivers, including their channel definitions, morphological features, sediment characteristics, forming processes, and energy expenditure features. Especially, the wandering channel pattern mainly develops in a low energy slope environment that is far less than the minimum energy slope required for transporting sediment load. So it usually presents unstable features. The braided channel pattern can exist where river energy is lower or higher than the minimum energy slope. Therefore, it is essential to distinguish these two channel patterns. The article also discusses prospects for studies in the future and points out that focusing on the physical mechanisms for channel formation, developing and refining the energy theory, and examining the differences and similarities of wandering channel and braided channel systematically can help to solve the problem of classifiying wandering rivers.