A study of landslide potential along the road in the Chi-sun watershed

2009年莫拉克風災連續豪雨，創下台灣50年來最大之降雨量；其中以高雄市旗山溪集水區遭受災害最為嚴重，形成數百處崩塌，造成集水區地形地貌與景物劇烈變化，尤以道路沿線受災嚴重。道路為民生必需之重要運輸管道，當災害導致道路崩壞，除造成交通不便外，嚴重者將危及鄰近保全對象安全，故建置完善道路安全之風險評估系統來評估道路沿線崩塌潛勢，為刻不容緩之議題。 本研究分析旗山溪集水區道路沿線之崩塌潛勢，利用SPOT衛星影像萃取莫拉克風災後集水區新增崩塌區位；結合災前之土地利用及地形資料，運用源頭崩塌潛勢、地形濕度指數、凹岸崩塌潛勢、上邊坡崩塌潛勢及集水區崩塌率等環境脆弱度指標之組合，藉以評估於莫拉克風災尺度下，道路沿線之崩塌潛勢，並以不安定指數(DVM)進行崩塌潛勢權重分級，繪製旗山溪集水區道路沿線崩塌潛勢之空間分布。 研究結果顯示，凹岸崩塌潛勢為道路沿線崩塌之主要影響指標，其權重為0.22，其次為地形濕度指數，權重為0.21；各崩塌潛勢因子所得之權重經計算後，將高、低兩類以Kappa分析評估分類之精度，整體準確度達79.2%，顯示此評估模式之預測精度良好。以高潛勢區域之崩塌率最高，此與莫拉克風災實際崩塌案例吻合，本模式可有效標出危險路段，供相關單位監測管理之用。The maximum rainfall over the past 50 years was recorded in 2009 by the typhoon Morakot, which brought continuous torrential rains. The Chi-sun watershed located in Kaoshing City was damaged severely and caused hundreds of landslides. The topography and landscape of the watershed were changed abruptly, and the most serious disasters were located along the roads. Road is the most important transportation and plays an essential role for the necessity of human life. Natural disasters caused road failure could result in traffic interrupt, and the worse situation could endanger the safety of adjacent protected targets. Therefore, there is a must issue to establish a risk analysis system for evaluating the potential landslides along the road. This study analyzed the potential landslides along the roads in Chi-sun watershed. Post-disaster landslides extracted using SPOT satellite imagery coupled with pre-disaster data of land use and DEM, and using the combination of several environmental vulnerability index such as headwater landslide potential, topographic wetness index, concave landslide potential, upper slope landslide potential to evaluate the landslide potential along the roads under the hazard scale of typhoon Morakot. In addition, grading the weight of landslide potential was calculated using Dangerous Value Method to delineate the spatial distribution of potential landslides along the roads in the Chi-sun watershed. The results show that the concave landslide potential with the weight of 0.22 is the main affecting indicator, topographic wetness index with the weight of 0.21 placed the second. After weighting all the parameters, the whole accuracy of the model can reach up to 79.2% in Kappa analysis, which was calculated from random sampling with 250 samples of high landslide potential and 250 samples of low landslide potential. The model developed in this study shows good performance in high landslide potential and good fitness comparing with field landslides. The model can be as the references of monitoring and management for the use of related authorities.目錄 摘要...................I ABSTRACT..............II 目錄...................IV 圖目錄.................VI 表目錄.................VII 第一章 前言..............1 1.1 研究動機.............1 1.2 研究目的.............1 1.3 內容架構與研究流程.....1 第二章 文獻回顧...........4 2.1 全球道路災害..........4 2.2 崩塌潛勢研究..........6 2.3 崩塌地判釋...........10 2.4 不安定指數...........11 2.5 準確度評估...........11 第三章 研究材料與方法......13 3.1 研究樣區概述.........13 3.2 研究材料............14 3.2.1 數值高程模型.......14 3.2.2 GIS圖資..........15 3.2.3 道路與土地利用.....18 3.3 研究方法............18 3.3.1 崩塌地萃取........18 3.3.2 群集分析..........19 3.3.3 不安定指數法 ......21 3.3.4 移動平均法........23 3.3.5 準確度評估........24 第四章 崩塌機制探討.......28 4.1 源頭崩塌潛勢.........28 4.2 地形濕度指數.........29 4.3 凹岸崩塌潛勢.........31 4.4 上邊坡崩塌潛勢.......32 4.5 集水區崩塌率.........33 第五章 結果與討論.........34 5.1 集水區崩塌萃取資訊....34 5.2 道路沿線脆弱度分析....35 5.2.1脆弱度權重分析......35 5.2.2脆弱度類型分析......37 5.2.3道路沿線崩塌潛勢分級...43 5.3 崩塌潛勢驗證.........45 5.3.1潛勢權重與實際崩塌驗證...45 5.3.2實際崩塌案例驗證........45 第六章 結論..............50 參考文獻.................51 圖目錄 圖1 研究流程圖............3 圖2 研究樣區地理位置圖.....13 圖3 莫拉克風災前後衛星影像..17 圖4 源頭集水區之空間分佈....29 圖5 道路沿線莫拉克風災後航照圖...30 圖6 以TWI及NDVI劃分道路崩塌點位之群集分布...31 圖7 凹岸崩塌潛勢示意圖.....32 圖8 豐丘明隧道上邊坡崩塌...33 圖9 道路與水系交點集水區崩塌分布圖...33 圖10 旗山溪崩塌地集水區新增崩塌分布圖...34 圖11 源頭崩塌之空間分佈...37 圖12 源頭崩塌潛勢於道路沿線之空間分布...38 圖13 地形濕度指數較高之崩塌航照圖...39 圖14 地形濕度指數於道路沿線崩塌潛勢之空間分布...39 圖15 凹岸崩塌航照圖......40 圖16 凹岸崩塌潛勢於道路沿線之空間分布...41 圖17 上邊坡崩塌潛勢於道路沿線之空間分布...42 圖18 集水區崩塌率於道路沿線之空間分布...43 圖19 道路沿線崩塌潛勢.....44 圖20 旗山溪集水區上游林道重點區位崩塌潛勢分佈圖...46 圖21 旗山溪集水區上游林道30K~35K易致災潛勢圖...46 圖22 小林村林道重點區位崩塌潛勢分佈圖...47 圖23 小林村林道2K~7K易致災潛勢圖...48 圖24 台21線重點區位崩塌潛勢分佈圖...49 圖25 台21線132K~136.5K易致災潛勢圖...49 表目錄 表1 近年全球各地災害案例....4 表2 崩塌潛勢相關研究.......6 表3 邊坡穩定評估方法之比較..9 表4 台灣目前可取得衛星影像資料類型比較...10 表5 基本圖資蒐集資料.......14 表6 SPOT衛星影像各光譜波段與其反射特性...16 表7 群集分析法............20 表8 影像分類誤差矩陣.......27 表9 集水區與道路崩塌資訊....35 表10 脆弱度因子權重分析.....36 表11 源頭崩塌資訊.........38 表12 上邊坡開發崩塌資訊....42 表13 道路與野溪交點集水區崩塌資訊...43 表14 各級潛勢路段之崩塌率...44 表15 潛勢分析與實際崩塌準確度評估...4