宁夏隆德县泥石流形成条件

Formation conditions of debris flows in Longde county of Ningxia

2013年,隆德县遭遇了50年一遇的强降雨,导致境内发生了17处泥石流。在野外详细调查的基础上,结合区域现有资料,从沟坡比降、物源和水源三个主要方面分析了隆德县泥石流的形成条件。结果表明：隆德县泥石流均分布于丘陵地貌区,坡度范围在20°~50°之间,相对高差在50~100m之间,为泥石流的发生提供了有利的地形地貌条件;流域内新近系（Ngn）桔红色砂质泥岩残坡积物,具有弱膨胀性,吸水后会发生一定程度的崩解软化,导致土体结构联结减弱、强度降低,构成了泥石流的物源;降雨是隆德县泥石流最主要的触发因素。通过实地调查与降雨数据分析,可知隆德县泥石流的形成主要受前期降雨的影响,属于前期降雨控制型泥石流。因此,可通过监测前期降雨,特别是间接前期降雨,对泥石流进行预警预报。

Longde county suffered a heavy rain of once every 50 years,resulting in 17 debris flows.Based on the detailed field investigation and geological environmental conditions of this region,the formation conditions of the debris flow were analyzed from 3aspects of the gradient of gully and slope,material sources and water conditions.The results indicated that the debris flows of Longde county were distributed in the hilly regions,where the slope was 20°~50°and the height difference was 50~100m.These were favorable geological and geomorphological conditions for debris flow.In the basin the residual soil of orange sandy mudstone of Neogene（Ngn）had the weak dilatability.A certain degree of degradation and softening would occur after immersed by water,resulting in the connection of structure and strength was weakened.Therefore,it was the material source of debris flow.Rainfall was the most important trigger factor of the debris flow.Depending on field investigation and data analysis,the formation of debris flow in Longde county was mainly affected by antecedent precipitation.They belonged to the antecedent precipitation control pattern.So the debris flows in Longde？county could be warned by monitoring the antecedent precipitation,especially the indirect antecedent precipitation.