黄河下游河床演变三大基本问题的研究

Three aspects of morphological evolution Processin the Lower Yellow River

断面极为宽浅，纵比降的塑造，以致河道严重淤积，是黄河下游河床演变的三大基本问题．黄河下游的主要特征是强烈游荡、严重淤积．这也是黄河一切灾难的主要原因．前者是断面太宽浅以及比降偏陡而直接引起的问题．河道形态由来水来沙搭配关系决定．水沙关系Ｑｓ＝ＫＱｍ的ｍ值小于２５的，属于大水来沙偏少而小水来沙偏多，滩地不易淤高而河槽易于淤浅，要形成多汊宽浅游荡性河流．反之，ｍ大于２５的则形成单股窄深蠕动性河流．黄河下游ｍ约为２，故成为强烈游荡的宽浅河道．后者则是河道输沙能力的形成问题，是由纵、横断面的配合决定的．泥沙输移的沿程淤积分选，大量细颗粒长远输送而于几千年前就造成了偏小的纵比降，与宽浅的断面配合而成的输沙能力远小于流域来沙量，是黄河严重淤积的原因．

It is pointed out that the morphological evolution process of the lower Yellow River has three elementary aspects:shallow cross section,mild longitudinal slope and intensive amount of aggradation.One of the main characteristics of the River is frequently shifting of the main channel,resulted from more shallow cross section and more steep longitudinal slope.The other one is severe siltation due to the formation of the sediment transport capacity related to the geometric features of the longitudinal profile and cross section.The rive[BF]r's[BFQ] geometry depends on the relationship between sediment and water transport.The Lower Yellow River belongs to a shallow river with frequently shifting of the main channel.Siltation along the river has formed the mild riverbed slope thousands of years ago.The silt transport capacity generated by mild bed slope and shallow cross section is much smaller than the inflow sediment from the watershed.This is the cause of consistent serious siltation of the Lower Yellow River.