“5·12”地震后汶川县泥石流特征与演化分析

CHARACTERISTICS AND EVOLUTION OF DEBRIS FLOWS IN WENCHUAN COUNTY AFTER“5·12”EARTHQUAKE

2008年“5·12”汶川地震极大地改变了震区泥石流的特征,不仅增强了泥石流的活动性,同时也使得震区在相当长的时间内都要面临泥石流的威胁。本文基于前人大量的研究成果,并利用遥感解译结合现场调查等手段,分析了汶川县泥石流沟道纵坡降、沟壑密度、两岸坡度等基本发育特征;进而分析了地震前后汶川县降雨分布及泥石流相关降雨参数变化特征。结果显示,流域内泥石流沟的沟壑密度在0.2~4之间,属于微度土壤侵蚀区域,泥石流的沟床纵坡降偏大,有利于泥石流的发生;泥石流流域内斜坡坡度多为30°~40°,有利于灾害的发生;震后汶川县年均降雨量增加了5.17%,降雨多集中在7~9月份,降雨量由南及北逐渐降低;震后泥石流的降雨阈值在2008~2013年呈现缓慢回升的趋势,但2019年又有所下降,预计恢复到震前水平尚需要一定时间;同时震后汶川县泥石流物源丰富,震后物源量呈现“震荡式衰减”的演化趋势,但体量仍然很大,对泥石流仍需坚持监测预警工作。

The 2008“5.12”Wenchuan earthquake greatly changed the characteristics of debris flows in the earthquake zone.The earthquake not only enhanced the activity of debris flows,but also made the earthquake area under the threat of debris flows for a long time.During the past 10 years after the earthquake,debris flows occurred frequently.It is of great significance to study the characteristics and development trend of debris flows in Wenchuan County.We analyze the longitudinal gradient,gully density and slope gradient in Wenchuan County by means of remote sensing interpretation and field investigation.We further analyze the rainfall spatial and temporal trends and critical rainfall characteristics of debris flows in Wenchuan County by collecting rainfall data and previous research.According to the study,the average annual rainfall in Wenchuan County increased by 5.17%after the earthquake.The rainfall was mainly in July and September,the amount of rainfall decreased gradually from north to south.The gully density of debris flow gully is between 0.2 and 4,which belongs to the soil erosion area of the micro-degree.The longitudinal gradient of debris flow is large,which is conducive to the occurrence of debris flow.The slope gradient of debris flows is 30°~40°,which is conducive to the occurrence of disasters.The rainfall threshold of the post-earthquake debris flow shows a slow increased in 2008-2013,but declined in 2019.It is expected that it can take a long time to return to the pre-earthquake levels.The provenance of debris flows in Wenchuan County is abundant,and the amount of provenance in the earthquake is decreased in a fluctuating tendency.