白龙江流域泥石流危险性评价

Hazard assessment of debris flow in Bailong River Basin

泥石流是暴发在山区小流域内的特殊地质灾害,泥石流危险度评价是泥石流灾害风险预测、评价和防治的前提。本文以流域单元为评价单元,选取沟床比降、泥石流规模和堵江程度3个因子,构建危险性评价模型,提出流域尺度的危险性评价方法。以甘肃省陇南地区白龙江流域为研究区,应用GIS技术,利用数字高程模型(DEM)数据,建立以水文响应单元为基本评价单元,应用危险度模型计算研究区泥石流危险度,划分危险度等级,编制泥石流危险性评价结果图。结果表明:处于中度危险以上的泥石流沟数量占78%,其中,极高度危险的泥石流沟占25.3%。评价结果与实际灾情吻合,可为白龙江流域防灾减灾提供参考依据。

[Background] Debris flow is a widely distributed geological hazard in the mountainous area,and the hazard assessment of debris flow is essential for its prediction,risk evaluation and prevention.The Wenchuan earthquake has disturbed the geological condition of southern Gansu province,which not only produced abundant loose material to new debris flow formation but also triggered the recurrences of some debris flows in idle. The Bailong River Basin is located in the South Gansu province,where severe debris flow occurred during the Wenchuan earthquake in 2008,thus it was selected for this study.[Methods]A watershed unit was taken as the evaluation unit,and the evaluation unit was determined using GIS technology with digital elevation model（ DEM） data. A debris flow hazard assessment model at watershed-scale was proposed based on the gradient of debris flow gully,the scale of debris flow and the level of potential river blockage. By applying the proposed hazard assessment model for Bailong River Basin,the hazard degree of debris flow was obtained as 5 levels of very high,high,moderate,low,and very low,and a hazard map of debris flows was constructed for Bailong River Basin. [Results] The assessment results indicated that there were 2 debris flows at very low hazardous level,accounting for1. 3% of the total debris flows,31 debris flows（ 20. 7%） at low level,60 debris flows（ 40%） at moderate level,19 debris flows（ 12. 7%） at high level,and 38 debris flows（ 25. 3%） at very high level. The 117 debris flow gullies were at the moderate hazardous level or above,accounting for 78% of150 total gullies. Validated by the field investigation and historical debris flow events,the debris flows in Luojiayu,Sanyanyu,Yuzi,liangshui and Shimen gullies were at very high hazardous level,which was consistent with the assessment result. [Conclusions] It is scientific to take a watershed unit as evaluation unit because it can reflect the features of valleys,topography and landform conditions when debris flow occurs. On this basis,the assessment factors are selected from the debris flow energy,source and disaster degree to establish an index system for assessing the hazard of debris flow. Through field investigations,it is confirmed that the assessment results by model are consistent with the actual situation of debris flow,thus this model may be used to predict the occurrence of debris flow in the Bailong River Basin.