大渡河上游沙耳沟泥石流震后特征及其发展趋势

CHARACTERISTICS AND DEVELOPMENT TRENDS OF SHAER DEBRIS FLOW AFFECTED BY "5.12" EARTHQUAKE IN UPPER DADU RIVER,CHINA

沙耳沟是一条老泥石流沟,处于＂5.12＂地震的严重波及区。为了研究地震对严重波及区泥石流沟的影响,通过详细的野外调查和勘查,对沙耳沟泥石流震后基本特征和发展趋势进行了探讨。沙耳沟泥石流的性质可判定为＂中频率-中~大规模-较高粘度泥石质泥石流＂,具有暴雨激发、成灾速度快、危害严重等特点,其危害作用主要为冲毁和淤埋。泥石流物源主要以沟床质起动、沟源侵蚀和沟岸崩滑补给为主,沟内固体物源方量约130.0×104m3,其中可能参与泥石流活动的固体物源动储量约30.0×104m3,已经具备暴发中-大规模泥石流的可能性。根据计算,在50 a一遇的暴雨作用下,一次泥石流总量超过9×104m3;在100 a一遇及更低频率的暴雨作用下,一次泥石流总量超过13×104m3。通过研究发现,＂5.12＂地震对地震严重波及区的泥石流沟有一定的影响,但影响不十分明显,其发展趋势仍按自身规律进行演化。

Shaer Gully,an old debris flow gully,the first order right branch of Dadu River,is located in Jinchuan County,Sichuan Province,which is one of the seriously affected counties during ＂5.12＂ Earthquake.In order to study the earthquake＇s influence on debris flow gullies in affected areas during ＂5.12＂ Earthquake,we studied the characteristics and development trends of debris flow in Shaer Gully based on detailed field survey and investigation.The debris flows of this gully could be defined as median frequency,medium-large scale,higher viscosity,muddy and bouldery debris flows.The main characteristics of debris flows were as follows：（1）Rainstorm was main triggering condition;（2）It caused rapidly disasters and serious damages;（3）Main harming actions were destruction and burying.The amounts of loose materials had further increased in this gully due to the earthquake and reached 130.0×104 m3 in volume,approximate 30.0×104 m3 of which could be involved in subsequent debris flows.Consequently this gully has already had the possibility of breaking out large scale debris flows.According to calculation results,the once total volume of debris flow exceeded 9×104 m3 and 13×104 m3 under the precipitation of 50 years cycle and 100 years cycle,respectively.From this study,we found that the earthquake had some influences on debris flow gullies in these affected areas,but it was not serious.Its development trends had no significant change.