汶川震区寿溪河流域崩滑物源演化特征分析

Analysing Evolution Characteristics of Landslide Deposits in Shouxi River Basin in the Wenchuan Earthquake Zone

崩滑堆积体是洪沙灾害的主要物源之一,研究其时空分布与演化特征对洪沙灾害易灾区早期识别、风险区的研判有重要作用。为探究汶川震区洪沙灾害崩滑物源时空演化特征,选择汶川典型流域寿溪河流域为研究区域,对寿溪河流域2007、2009、2012、2015、2018年5期高分遥感数据进行崩滑物源解译,建立了研究区震前—震后崩滑物源的长时间序列数据集,并利用确定性系数(certainty factor,CF),结合高程、坡度、坡向、距沟道距离、距断层距离、年均降水量等关键控制因子,定量分析崩滑物源在各个因子上的活跃程度及演变特征,计算植被覆盖度(vegetation fraction coverage,VFC)与植被恢复速率(vegetation coverage recovery rate,VCRR),探讨植被恢复对崩滑物源活动的影响。结果表明:5期解译的崩滑物源面积分别为15.68×10^(4)、442.45×10^(4)、252.86×10^(4)、146.07×10^(4)、98.97×10^(4) m2,且以指数函数的模式衰减,预测物源面积恢复到震前水平的时间约为21 a。研究区震后崩滑物源活动性最强的区域的高程为1 200~2 400 m,坡度为大于60°,坡向为SE,距沟道距离为小于800 m,距断层距离为小于1 500 m,年均降水量为830~850 mm。演化趋势为崩滑物源在高程大于2 000 m、坡度小于40°、距沟道距离大于200 m、距断层距离大于1 500 m、年均降水量大于840 mm的区域的活动性增强,在坡向为E、SE、S侧活动性减弱。震后VFC随着时间的推移以线性形式增长,预测震后至少14 a植被覆盖度恢复到震前水平;2012、2015、2018年植被恢复中等及以上的区域分别占37.32%、64.24%、70.69%;在植被恢复程度高的地方,崩滑体的活动性低且随着时间的推移而降低,植被的恢复能有效减弱崩滑物源的活动。以上研究对于丰富崩滑物源演化理论与洪沙灾害风险预测具有重要意义。

Landslide deposits are one of the main sources of flash flood and sediment disaster,and their spatio-temporal distribution and evolution characteristics play an important role in the early identification of flash flood and sediment disaster areas and the study of risk areas.In order to explore the spatio-temporal evolution characteristics of landslide deposits in the Wenchuan earthquake zone,this paper selected Shouxi River Basin,a typical basin in Wenchuan,as the research area,and respectively interpreted the landslide deposits based on the five stage high-resolu-tion remote sensing images in 2007, 2009, 2012, 2015 and 2018, and established a long time series data set of “pre-earthquake and post-earth-quake” landslide deposits in the research area, and combined with the key control factors such as elevation, slope, aspect, distance from channel , distance from fault and average annual precipitation, quantitatively analyzed the relationship between evolution characteristics of landslide depos-its and each factor based on certainty factor model (CF), finally calculated the vegetation fraction coverage (VFC) and the vegetation coverage re-covery rate (VCRR) to explore the effect of vegetation restoration on landslide deposits activities. The research results showed that the areas of landslide deposits of five stage images were 15.68×10^(4) m2, 442.45×10^(4) m2, 252.86×10^(4) m2, 146.07×10^(4) m2, 98.97×10^(4) m2, and were attenuated by exponential function mode. In addition, the predicted time for the area of landslide deposits to recover to the pre-earthquake level is about 21 a. The area with the strongest activity of post-earthquake landslide deposits in the study area is 1 200~2 400 m in elevation, 60° in slope, SE in slope direction, less than 800 m in distance from channel , less than 1 500 m in distance from fault and 830~850 mm in the average annual precipita-tion . The evolution trend is that the activity of the landslide deposits increases in the area with an elevation of more than 2 000 m, a slope of less than 40°, a distance of more than 200 m from the channel ,a distance of more than 1 500 m from the fault, the average annual precipitation is more than 840 and decrease in the aspect of E, SE and S sides. VFC increases linearly with time after the earthquake, and it is predicted that the vegeta-tion coverage will return to the pre-earthquake level at least 14 years after the earthquake. In 2012, 2015 and 2018, the areas with moderate or above VCRR account for 37.32%, 64.24% and 70.69%, respectively. In places with high VCRR, the activity of landslide deposits is low and de-creases with time, and vegetation restoration can effectively reduce the activity of landslide deposits. The above research is of great significance to enrich the theory of landslide deposits evolution and flash flood and sediment disaster risk prediction.