Debris flow risk assessment considering different rainfall sensitivity: A case study in southeast Tibet
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摘要:
藏东南是泥石流发生的高频地区,也是G318国道铁路的途径之地,泥石流对当地社会发展和重大工程建设构成严重的威胁。文中针对藏东南区域的条件选取了距公路距离、距河流距离、距断层距离、高程、坡度、降雨、NDVI等11个致灾因子来研究该地区的泥石流发生规律。在ArcGIS中导出并分析泥石流点各因子数据,进行相关性检验和建立因子敏感度等级。利用层次分析法计算权重后,结合因子敏感图层制作2015年藏东南地区泥石流危险分布图来检验模型的正确性。针对不同降雨敏感度制作不同的危险分布图来预测未来的泥石流易发区。当全区降雨敏感度为3时,藏东南近一半地区都是泥石流的极高易发区,G318国道沿线都处于高危险地区中。降雨敏感度为2时,藏东南没有极高易发区,全区危险指数大大降低,G318国道沿线高危险部分占84.56%。结果表明降雨量对研究地区泥石流的危险性分布影响较大,该研究成果可为藏东南的社会发展及重大工程基础建设提供理论支撑。
Abstract:Southeast Tibet is an area with high frequency of debris flow, and also the place G318 pass through. Debris flow poses a serious threat to local social development and major engineering construction. In this paper, according to the conditions of southeast Tibet, 11 disaster-causing factors such as highway distance, watershed distance, fault distance, elevation, slope, rainfall and NDVI etc. are selected to study the occurrence regularity of debris flow in this area. Each factor data of debris flow point is derived and analyzed in ArcGIS, correlation test is carried out and factor sensitivity grade is established. After calculating the weights by AHP, the risk distribution map of debris flow in southeast Tibet in 2015 was made by combining factor sensitive layers to verify the correctness of the model. Different risk distribution maps are made according to different rainfall sensitivities to predict the future debris flow prone areas. When the rainfall sensitivity of the whole region is 3, nearly half of the southeast Tibet is highly prone to debris flow, and all along G318 are in high risk areas. When the rainfall sensitivity is 2, there is no extremely high risk area in southeast Tibet, the risk index of the whole region is greatly reduced, and the high risk part along G318 accounts for 84.56%. The results show that rainfall has a great influence on the risk distribution of debris flow in the study area. The research results can provide theoretical support for the social development and major project construction in southeast Tibet.
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Key words:
- southeast Tibet /
- debris flow /
- rainfall sensitivity /
- ArcGIS /
- analytic hierarchy process /
- risk level
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表 1 近8年地质灾害调查报告
Table 1. Geological disaster investigation report in recent 8 years
年份 2019 2018 2017 2016 2015 2013 2012 2011 发生地质灾害数量/次 56 67 59 185 82 138 59 139 泥石流数量/次 30 39 23 118 62 75 35 77 泥石流灾害占比/% 54 58 39 64 76 54 59 55 注:西藏历史年鉴中没有公开2014年数据。 表 2 泥石流致灾因子及数据来源
Table 2. Debris flow disaster factors and data sources
一级因子 二级因子 数据来源 固体物源 距公路距离 1∶100万全国基础地理信息数据 距河道距离 距断层距离 中国地震和火山 地形 高程 ASTGTM2 DEM30m 坡度 坡向 水源 降雨 中国科学院资源环境
科学与技术中心水文 诱发因子 植被覆盖率 土地利用率 地貌 地理空间数据云 表 3 泥石流7个致灾因子的相关性分析
Table 3. Correlation analysis of 7 disaster-causing factors of debris flow
指标 距公路距离 距河道距离 距断层距离 高程 坡度 植被覆盖率 土地利用率 距公路距离 1 距河道距离 0.520** 1 距断层距离 −0.076 −0.054 1 高程 0.259** 0.416** 0.263** 1 坡度 0.171** 0.175** −0.021 0.245** 1 植被覆盖率 0.185** 0.220** −0.160** −0.199** 0.174** 1 土地利用率 0.094 0.084 0.188** 0.298** 0.105 −0.341** 1 表 4 量化表
Table 4. Quantitative table
因素i比因素j 量化值 同等 1 稍微 3 较强 5 强烈 7 极端 9 两相邻判断中间值 2,4,6,8 倒数 aij=1/aij 表 5 第一准则层判断矩阵
Table 5. The judgment matrix of first criterion layer
固体因子B1 水源因子B2 地形因子B3 诱发因子B4 固体因子B1 1 1/6 1/4 3 水源因子B2 6 1 4 8 地形因子B3 4 1/4 1 5 诱发因子B4 1/3 1/8 1/5 1 表 6 第二准则层判断矩阵
Table 6. The judgment matrix of second criterion layer
距公路距离C1 距河道距离C2 距断层距离C3 固体物源
因子判断
矩阵距公路距离C1 1 4 7 距河道距离C2 1/4 1 4 距断层距离C3 1/7 1/4 1 高程C4 坡度C5 坡向C6 地形判断
因子矩阵高程C4 1 1/7 1/3 坡度C5 7 1 4 坡向C6 3 1/4 1 降雨C7 水文C8 水源判断
因子矩阵降雨C7 1 7 水文C8 1/7 1 植被覆盖率C9 土地利用率C10 地貌C11 诱发因子
判断矩阵植被覆盖率C9 1 2 4 土地利用率C10 1/2 1 3 地貌C11 1/4 1/3 1 表 7 致灾因子敏感度及权重
Table 7. Sensitivity and weight of disaster-inducing factors
第一准则层 第二准则层 分类 泥石流数量 总占比/% 敏感度 权重 固体
物源
因子距公路距离C1 [0, 700),[700, 1 400) 105,82 57.4 3 0.0688 [1 400, 2100),[2 100, 2 800), [2 800,3 500) 45,30,24 30.4 2 [3 500, 10 850) 40 12.3 1 距河道距离C2 [0, 1 400) 197 60.4 3 0.0234 [1 400, 2 800) 96 29.4 2 [2 800, 5 600) 34 10.4 1 距断层距离C3 [0, 5 000) 105 32.2 3 0.0078 [5 000, 10 000),[10 000, 20 000) 78,89 51.2 2 [20 000, 30 000),[30 000, 40 000) 43,11 16.6 1 地形
因子高程C4 [3 500, 4 500) 193 59.2 3 0.02125 [2 500, 3 500) 90 27.6 2 [1 500, 2 500),[4 500, 5 500) 16,27 13.2 1 坡度C5 [20, 30),[30, 40) 76,89 50.6 3 0.17525 [0, 10),[10, 20),[40, 50) 43,57,49 45.7 2 [50, 60) 12 03.7 1 坡向C6 西北,西南,西 52,53,50 47.5 3 0.05325 南,东,东南 47,40,37 38.0 2 北,东北 29,28 17.5 1 水源
因子年均降雨量
(2001—2009年)
C7[700, 800) 127 39.0 3 0.528 [600, 700),[800, 900) 82,72 47.2 2 [500, 600),[900, 1 300) 11/34 13.8 1 水文C8 森林生态系统 180 55.2 3 0.072 草地生态系统 105 32.2 2 湿地,农田,裸土地系统 17,8,15 12.3 1 诱发
因子植被
覆盖率
C9[0.6, 0.7),[0.7, 0.8) 117,118 72.1 3 0.02785 [0.4, 0.5),[0.5, 0.6) 28,39 20.6 2 [0.1, 0.4) 23 7.1 1 土地
利用率
C10[20, 30) 198 60.7 3 0.016 [30, 40) 102 31.3 2 [10, 20),[40, 50),[60, 70) 9,11,16 11.0 1 地貌
C11高海拔山地 240 73.6 3 0.00615 中高海拔平原 58 17.8 2 其余地貌 38 11.7 1 表 8 图层数值与易发性对应表
Table 8. Corresponding table of layer values and debris flow susceptibility
图层数值 易发性 [0, 1) 非易发区(几乎不会发生泥石流) [1, 1.5) 低易发区(极少发生泥石流) [1.5, 2) 中易发区(受体条件影响容易发生泥石流) [2, 3) 高易发区 [2, 2.3) 低高易发区 [2.3, 2.6) 中高易发区 [2.6, 3) 极高易发区 表 9 2015重大泥石流事件信息
Table 9. Information on major debris flow events in 2015
县市 位置 发生日期 来源 预测易发性 昌都边坝无名冰湖 G318国道附近 2015年7月3日 《西藏冰湖溃决灾害事件极端气候特征》 中易发区 昌都边坝金岭乡结玉村江卡自然村 边坝县讲卡村 2015年7月3日 中国天气网西藏站 中易发区 林芝扎木弄沟泥石流 波密县易贡藏布河域附近 2015年8月16日 《西藏林芝扎木弄沟泥石流规模变化趋势研究》 中易发区 林芝巴宜区 排龙乡河谷路段 2015年8月17日 中国新闻网 高易发区 昌都边坝 边坝镇普玉二村荣达自然村 2015年9月12日 人民网 中易发区 林芝 G318国道林芝境内 2015年8月—2015年9月 拉萨新华社 高易发区 -
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