基于小流域的地震扰动区降雨型滑坡泥石流危险性评价方法

Hazard Assessment on Rainfall-Triggered Landslide and Debris Flow in the Seismic Disturbance Area at Watershed Level

地震扰动区存在大量震裂松散坡体,在持续或者密集的降雨条件下极易转化为滑坡灾害。同时,滑坡又会给泥石流提供大量松散固体物质,增加泥石流的危险性。因此,在震区,灾害通常以"链"的形式出现,比单一灾种危害性大。为了更有效地对地质灾害危险性进行评价,笔者将滑坡、泥石流作为灾害链,综合地加以分析和研究。选择5·12汶川大地震中受灾严重的都江堰市白沙河流域的17条泥石流沟作为研究区,建立滑坡-泥石流危险性评价耦合模型,研究24h不同降雨量条件下小流域滑坡泥石流危险性的变化。耦合模型包括了坡体稳定性评价模型,水文模型及以泥石流规模、发生频率、流域面积、主沟长度、流域高差、切割密度、不稳定斜坡比为评价因子的泥石流危险性评价统计模型。研究结果表明:随着降雨量的增大,参与泥石流活动的松散物质方量持续增加,但当24h降雨量超过200mm后,泥石流沟的危险度等级不再发生变化;17条泥石流沟中4条为中危险度,12条为高危险度,1条为极高危险度。这说明研究区地质灾害问题相当严峻,在多雨季节存在泥石流群发的可能性,直接威胁到居住在泥石流沟附近的人民群众生命财产安全;因此,对于有直接危害对象的高危险度及其以上的泥石流沟,应该按照高等级设防标准进行工程治理及发布预警报。同时也说明,将滑坡、泥石流作为灾害链研究具必要性和可行性。

There are many loose slopes existed in the seismic disturbance area .Landslides and debris flow can be easily induced by a heavy or concentrated rainfall .The hazards often occur in a form of chain in an earthquake region with a severer harm than the one caused by a single disaster .In order to evaluate the geological hazards effectively ,we regard the landslide and debris flow as a disaster chain and conduct the analysis synthetically .A coupled model has been developed to assess the hazard degree of debris flow induced by the different 24 h precipitation at watershed level in Baishahe watershed of Dujiangyan City in Sichuan Province .The model comprises of a landslide susceptibility evaluation model ,a stability model , a hydrological model to predict unstable slopes and determine the amount of landslides to be involved , and a statistical model to evaluate the hazard degree of debris flow gully by selecting debris flow volume , frequency ,basin area ,main gully length ,height difference ,cutting density ,and the ratio of unstable gully bed as the evaluation parameters .The results show that the volume of loose material involved in debris flow increase with the intensity of rainfall .However ,when 24 h rainfall is over 200 mm ,the hazard degree of debris flow does not change any more .Among the 17 debris flows ,four debris flows are middle hazardous ,twelve debris flows are high hazardous ,and one debris flow is very high .It indicates that the potential geological hazard is quite serious in the study area .During the rainy season ,17 debris flows might concentratedly outbreak ; which would directly threaten the nearby human lives and properties .The protection engineering and early‐alert should be set to eliminate the hazards caused by the debris flows in comply with the high level fortification standard .By the way ,it’s necessary to take landslide and debris flow as a disaster chain to make the hazard assessment .