西藏帕隆藏布泥石流沟谷纵剖面形态统计分析

A statistical analysis on longitudinal profile shape of debris flow valley along Palongzangbu River in Tibet

沟谷纵剖面形态既表征暴雨泥石流发育的地貌条件 ,又与水动力相关 ,是影响泥石流发肓的重要因素。西藏帕隆藏布是典型的冰川泥石流区 ,其干流然乌至迫龙段右岸分布 5 9条各类泥石流沟。统计分析表明 ,从帕隆藏布下游段向上游段 ,这些泥石流沟谷纵剖面形态有由下凹抛物线形向上凸抛物线形演变的趋势 ,形态指数N有由大变小之趋势 ,反映帕隆藏布河谷地貌演化溯源传递的进程。按特大型、一般性、潜在型泥石流沟的顺序 ,有纵剖面形态由凹至凸、N值由大至小的总体趋势 ,反映泥石流活动性与纵剖面形态的关系。冰雪融水型泥石流与雨水型泥石流相比 ,N值较小 ,纵剖面形态偏凸 。

Longitudinal profile shape of a debris flow valley can show morphologic condition of developing debris flow.It is also interrelated to waterpower and is a important element influencing development of debris flow. The Palongzangbu River basin in Tibet is a model area of glacier debris flow, and 59 debris flow valleys of different type are distributed along north bank of the main stream from Ranwu to Palong. It is indicated with statistical analysis that longitudinal profile shapes of these debris flow valleys have change trend from a concave parabola pattern to a convex one, and values of the shape index N have a increase trend, from lower reach to upper reach of the river. The trends reflect conveyer process of headward erosion in valley geomorphology of the river. General change trend of longitudinal profile shape from concave to convex and increase trend of value N ,in order of debris flow valleys of the especially big type,the ordinary and the potential type,reflect relationship between activity of the debris flows and longitudinal profile shape of the valleys. The longitudinal profile shape of ice snow melt water debris flow is more convex and its value N is more small in comparison with the rainwater debris flow valley, and special character of ice snow melt water debris flow is indicated.