岷江上游大白杨沟泥石流特征及成因

大白杨沟流域位于岷江上游四川省茂县境内,处于叠溪镇较场山字型构造北端。该沟曾于1935年和1991年暴发过两次较大规模泥石流灾害,其中1935年暴发的泥石流受1933年叠溪7.5级地震影响,规模很大,其泥石流峰值流量达到557 m3/s。通过对大白杨沟流域两条支沟(小沟、大沟)的地形条件、水源条件及物源条件的特征分析,得出两条支沟具有形成泥石流的充分条件:(1)大沟沟道平均纵比降275‰,小沟为398‰,相对高差达2 023 m;(2)大沟拥有的物源总量为29.21万m3,小沟达到42.01万m3,物源丰富。这些条件很好地解释了小沟泥石流的强活动性。对后期泥石流的形成机制进行分析,大沟以"消防水管效应"形成泥石流为主,小沟则以"消防水管效应"和堰塞体溃决两种方式形成泥石流。最后,通过泥痕法还原了历史泥石流流量,并对后期泥石流流量做了较合理的预测,为大白杨沟泥石流灾害防治提供可靠的数据。

Features and Formation Mechanism of Debris Flow in Dabaiyang Gully in Upper Reaches of Minjiang River

The Dabaiyang gully is located at the Jiaochang epsilon-type structure in the north of Diexi town,Maoxian County,Sichuan Province,which is in upper reaches of Minjiang River.Two large-scale flow debris events occurred in the gully in 1935 and 1991,and the flow debris in 1935 was caused by the 1933 Diexi Earthquake(Ms=7.5) which is huge with peak flow of 557 m3/s.After the analysis of the landform,available loose materials and water conditions of two tributaries(Dagou and Xiaogou gullies) in Dabaiyang gully,it was obtained that there are sufficient conditions for the formation of tributary debris flow,which explains the intense activity of debris flow in the Xiaogou gully:(1)the average longitudinal gradient is 275‰ in the Dagou gully and 398‰ in the Xiaogou gully,and the relative altitude is 2,023 m;(2)the total amount of loose materials is 292,100 m3 in the Dagou gully and 420,100 m3 in the Xiaogou gully,and the source of materials is abundant.The formation mechanism of debris flow was also analyzed.It reveals that the formation of debris flow caused by the fire hose effect in the Dagou gully,and by the fire hose effect and the burst of barrage body in the Xiaogou gully.The flux of historical debris flow was calculated by mud trace investigation method,and the flux of future debris flow was appropriately forecasted,which provides valuable data for preventing debris flow disaster in Dabaiyang gully.