根據文獻資料，堰塞湖潰決時間通常很短，相對於地震引致之堰塞湖，豪雨引致之堰塞湖事件，通常文獻報導較少，且相關描述相當不完整。為增添豪雨引致堰塞湖完整案例，有必要發展壩體幾何形狀建立或重建技術，以有效獲得快速潰決之壩體地形基本參數。本研究目標為建立快速評估堰塞湖天然壩幾何形狀之方法，並先以未潰決之那瑪夏鄉堰塞湖為驗證案例，再應用於已潰決之小林村堰塞湖案例。首先利用災前DTM資料、災後航照圖，配合野外調查，以重建那瑪夏鄉堰塞湖天然壩幾何形狀，並與實測地形比較，以驗證本研究建議之壩體重建方法。其次再以同樣方法，額外考量崩塌與壩體積平衡以及堰塞湖的溢流時間，以重建小林村堰塞湖天然壩幾何形狀，並進行壩體穩定性分析。根據本研究建議之壩體幾何形狀快速重建技術，那瑪夏鄉堰塞湖之壩體積為8.91 million m3，溢流點之壩高為與最大壩高分別為60 m及68 m，壩頂寬(沿河道)為2202 m，最大壩頂長(跨河道)及通過溢流點之壩頂長分別為213 m及179 m，與實測地形資料比較，本研究建立之天然壩幾何形狀重建技術可合理地評估天然壩幾何特徵；小林村堰塞湖天然壩壩體積則為15.34 million m3，溢流點之壩高及最大壩高分別為44 m及60 m，壩頂寬(沿河道)為1554 m，最大壩頂長(跨河道)及通過溢流點之壩頂長分別為500 m及370 m，根據壩體材料組成、推論之壩體幾何形狀與水文參數研判，小林村堰塞湖天然壩潰壩為溢流造成，與邊坡破壞或管湧關聯性較低。 According to literature, landslide dams usually collapse within a short time. Landslide dams are largely triggered by heavy rainfall more so than by earthquakes. Therefore, it is critical to develop a technique for reconstructimg the dam geometry, and to aollect some topography and hydrologic parameters, and to collect some topography and hydrologic parameters, then proceed with the statistical analysis. Typhoon Morakot brought a huge amount of rainfall, which caused many landslide dams in Southern Taiwan in 2009. We have used the Namasiam landslide dam as a basis for this study. DTM and aerial photography is used to reconstruct the dam geometry. The same is conducted for the Xiaolin landslide dam. Particular attention has been paid to stay within the budget and timeframe set. In summary, the total volume of the Namasia landslide dam is estimated to be 8.91 million m3, the dam breach hight is 60 m, the maximum dam height are 68 m, the dam width (along valley) is 2202 m, the maximum of dam length (across valley) is 213 m, and the outflow through the breach to the dam is 179 m. The total volume of the Xiaolin landslide dam is estimated to be 15.34 million m3, the dam breach hight is 44 m, the maximum dam height is 60 m, the dam width (along valley) is 1554 m, the maximum of dam length (across valley) is 500 m and flow through the breaching point of dam length is 370 m. The Xiaolin landslide dams and the Namasia landslide dams were classified as unstable based on DBI and discriminant analysis. The results can enable natural dams to be formed and the assessment of landslide dam stability.
