华北平原河流纵剖面

LONGITUDINAL PROFILES OF THE STREAMS ON THE NORTH CHINA PLAIN

本文用下凹度指标定量地描述河流纵剖面特征,华北平原诸河下凹型的纵剖面不仅与河长有关,而且也与水能有关。在综合分析影响河流纵比降因素的基础上,提出了构造运动的形变率、床砂粒径和来沙系数三要素的复式回归方程,此式体现了内外营力对河流比降的影响。

It is generally outlined by the forerunners,that the down- concave longitudinal profile of the streams means that the greater the rate of increase of discharge downstreams, the faster the sediment concentration decreases, and the smaller the sediment constitution, the greater the concavity of the longitudinal profile is.In this paper,the features of the stream of longitudinal profile have been quantitatively described by means of the index of cencavity, the concave longitudinal profiles of the streams on the North China plain are not only the function of the river length, but also the function of hydraulic energy.At present, the adjustment of the channel gradient is only shown by the experimental formulas based on bed material and discharge, which can only reflect the action of exogenic force due to relative subsidence of the North China plain,and different movements inheriting from the original stucture, especially the features of the tilting neotectonic movement, the rate of crustal deformation, which is different in various geomorphic units, can influence the form of the longitudinal profile of the stream and the adjustment of channel gradient, which is the action of the endogene force.As the factors affecting the adjustment of the channel gradient are analysed, the affections of both endogene and exogenic forces must be considered, because the formation, the development evolution of fluvial landforms result in the comprehensive action of the endogene and exogenic forces.According to the analysis of the influcence of endogene and exogenic forces on the forms of the longitudinal profile and channel gradient of the streams in the North China plain, an exponential multi-correlation equation among channel gradient(J)and rate of the crustal def ormation(T),the bed material size(D50) and the ratio of the sediment concentration (p) to discharge (Q) has been set up, as follows.with correlation coefficient r = 0.95 in cog. unit.