5·12地震后灾区泥石流危险度增加系数评价

5.12地震不仅直接引发了大量的崩塌、滑坡,而且降低流域内岩土体的强度,使其更易于受到侵蚀,从而为泥石流的形成提供丰富的固体物质。灾区震后泥石流活动频繁,并造成了较大的损失。泥石流沟的危险度评价是进行灾后重建的必要条件。选择震后固体物质增加量、地震烈度和堰塞坝规模这3个重要参数,提出了基于泥石流设计流量的震后泥石流危险度增加系数的评价方法。该方法通过计算地震后新增加的固体物质方量与通过配方法计算出的一次泥石流冲出物总量的比值,该比值与地震烈度影响系数的乘积及堰塞体蓄水量以流域50年一遇的流量排泄所需要时间3项之和来表达地震后泥石流危险度增加量。经灾区9条典型泥石流沟谷的计算验证,该方法做为一种新的方法,可快速、准确地评价5.12地震后灾区泥石流危险度的增加情况。

Evaluation of Debris Flow Risk in Worst-hit Area of Wenchuan Earthquake Based on Increase Coefficient

Wenchuan Earthquake not only induced a large amount of collapses and landslides immediately,but also reduced the strength of rock and soil mass in drainage basin,which makes them to be eroded more easily,so that abundant solid matter is provided for the formation of debris flows.The occurrence of debris flow is frequent in the disaster area after the earthquake and great losses have been caused.Evaluation on the risk degree of debris flow ditches is a necessary condition for post-disaster reconstruction.Three important parameters,i.e.,increment of solid matter,seismic intensity,and scale of barrier dam,are selected and evaluation method on increase coefficient of debris flow risk degree after earthquake is put forward based on designed debris flow.In this method,increase of debris flow risk degree is expressed by the ratio of added volume of solid matter to gross obtruding matter in a debris flow,seismic intensity multiplying the ratio,and time(hour)needed to drain water body in barrier dam with P_50% flux of the valley.By the validation of calculation for 9 typical debris flow ditches in the disaster area,the increase of debris flow risk degree in the May 12th disaster area after earthquake can be assessed by the new method,rapidly and precisely.