湖南慈利县滑坡灾害的临界降雨量阈值研究

科学合理地确定降雨诱发滑坡的预警阈值是区域防灾减灾的关键。以降雨型滑坡灾害高发的武陵山区为例,选取湖南慈利县1987—2011年逐年的历史滑坡灾害及降雨数据进行统计研究。首先,利用SPSS软件分析降雨与滑坡事件的相关性,发现该地区降雨型滑坡灾害主要受前3 d累积降雨量影响,且前期降雨有效系数仅为0.6;进而基于经验阈值分析模型,建立该地区分级预警的宏观平均有效降雨强度-降雨持续天数(I-D)降雨阈值曲线,并通过已知降雨滑坡事件进行空间验证;最后,考虑区内降雨型滑坡规模、滑体厚度及坡度的差异,分类建立了不同地质条件特性的I-D阈值曲线,发现临界降雨量阈值与滑坡规模及厚度呈显著正相关关系,而滑坡坡度则存在明显的最易发区间(25°~35°),此时临界降雨量阈值最小。研究结果可为武陵山区及相关地区降雨型滑坡的预测预报提供依据和借鉴。

Rainfall Thresholds of Rainfall-triggered Landslides in Cili County,Hunan Province

The key to hazard control and reduction for rainfall-triggered landslide is to identify the warning threshold scientifically. With Wuling mountain area as an example, historical landslide data and rainfall data from 1987 to 2011 were analyzed statistically using SPSS to reveal the relevance between rainfall and landslide event. Rainfall-triggered landslide in this region was mainly affected by the accumulated rainfall in the first three days of rainfall, and the effective coefficient of early-stage rainfall was only 0.6. Subsequently, based on the empirical threshold analysis model, the macroscopic I-D(intensity-duration) rainfall threshold curve for staged early-warning was established and verified through known rainfall landslide events. In view of the differences in scale, thickness, and slope gradient of landslides in the region, the I-D threshold curves corresponding to different geological conditions were built. Results unveiled that the rainfall threshold was evidently positively correlated with the scale and thickness of landslide, whereas slope gradient had an apparent susceptible interval (25° to 35°) where rainfall threshold reached the minimum. The conclusion offers reference for the forecast of rainfall landslide in Wuling mountain area and related areas.