流域特征曲线与泥石流活动

Characteristic Curves and Debris Flow Activity of a Valley

小流域是最活跃的地貌单元,泥石流是小流域演化中最剧烈的过程,是沟谷物质输移的最极端形式。以积分形式重新定义沟谷的比降,则比降曲线的变化直观反映了流域物质通过沟谷的改变。而流域的变化可以通过Strahler的流域的面积-高程曲线来表示。比降曲线与面积-高程曲线的自然联系,将泥石流活动问题与流域演化问题自然联系起来。以云南东川蒋家沟源地小流域面积-高程曲线为基础,具体讨论了流域可能发生泥石流的曲线形态和演化趋势。这样,有可能通过流域的形态特征来认识泥石流的长期演化。

Small valley is the most active agent in landscape evolution, and debris flowin it takes the most energetic role in mass transportation. In this paper we have systematically studied altitude-area （hypsometric）curve （in the sense of Strahler） and gradient curve （first proposed here） and their implication in debris flow. We propesean integral form to definethe gradient, i.e., the gradient can be determined by the double ratio of the area of the curve triangle bounded by the mainstream profile curve and the coordinate axes（with origin at the outlet） to the square of the horizontal length of the profile, J = 2S/L^2. In such a form, the gradient difference intuitively represents the mass off the valley through the streambed. Furthermore, this integral reduces the slope-channel equilibrium to a variation problem δJ = 0. On the other hand, integral of the hypsometric curve represents the total mass, and the variation reflects the mass transition of the whole valley. Thus the variation of gradient curve responds to variation of hypsometric curve. And relation between these two curves puts debris flow, the dramatic process of mass transport, up to the evolving phase of the valley. Fitted by a function in form of h^1/n=k^（1x）/（x ＋k）, hypsometric curve, and hence its variation, can be characterized by a parameter pair （k, n） with standing for the mass of valley and the shape of curve. And.we have analyzed the gravity potential energy of the valley mass in terms of the curve and found that evolution must be more sensible to the variation of which would intend to increase as the valley evolves. In a vase study, source tributaries of Jiangjia Gully present various hypsometric curves, failing into the （k, n） range between （0. 25, 0.20） and （0. 05, 0. 33 ）. And debris flow seems come from tributaries of parameters of （0.25, 0.2）and（0. 25, 0.36）. This makes distinguishing between different source areasand might as well lead to the understanding of debris flow revolution from characteristic curves of a basin.