堰塞湖形成潛感及潛勢圖-以旗山溪流域為例

Abstract

近年來由於國內發生地震或颱風豪雨於山區河流導致許多堰塞湖形成，若是堰塞湖的天然壩壩體潰決，壩體土石與堰塞湖湖水一起往下游流動則會對下游造成嚴重的災害。以防災角度而言，若能了解堰塞湖形成之潛感(機率)與形成之位置將有助於未來可能形成堰塞湖地區加強相關的防災工作。 本研究目的為引用鄭伊婷(2013)建立的”山崩後堰塞湖形成潛感模式”，修正其採用的山崩形態及崩塌類形成堰塞湖的路徑，以旗山溪為例採用較高精度的數值地形計算河道形成堰塞湖的潛勢，並繪製形成潛勢圖。數值地形由原先的30m精度提升為5m精度；山崩型態將土石流、岩屑崩滑、岩體滑動三種調整為土石流、落石、岩屑崩落、岩屑滑動及岩體滑動共五種，而在分析山崩潛感時簡化合併為土石流、崩落及滑動共三種型態；此外本研究亦改善岩屑崩落堰塞湖形成潛勢圖；透過崩塌後之運移路徑計算，挑選斜坡單元發生崩塌後會直接運移至河道者作為崩落潛感的分析單元；將其餘未直接運移至河道的斜坡單元合併成為聚積型土石流的分析單元，而其聚積型土石流分析單元結果與原先直接型土石流(集水區單元)不同。 本研究以旗山溪流域上游為例進行堰塞湖形成潛感運算及堰塞湖形成潛勢圖繪製，提出適當的三種山崩型態之堰塞湖形成潛感模式並且繪製出合理的堰塞湖形成潛勢圖，其成果與鄭伊婷(2013)之潛勢圖進行比較，比較結果顯示本研究之改善方法能有效提升堰塞湖形成潛勢圖精度，以決定可能的堰塞湖形成位置。

In Taiwan, earthquakes or rainfalls caused many natural dam lakes. If these dams break, the debris will flow to downstream and become terrible disasters. Susceptibility analysis for landslide dam formation may be helpful for the disaster prevention. This study aims to improve the susceptibility model of landslide dam formation proposed by Cheng(2013). The improvements include the increase of the DTM resolution from 30×30m to 5×5m, the change of landslide types based on the real environment, and the modification of the location of landslide dam caused by rock/debris falls. Based on the proposed modified susceptibility model, the susceptibility of landslide dam development and its map along the Chi-Shan river were presented. Compared with the Cheng’s(2013) results, the proposed modified model Effectively enhance the susceptibility analysis and mapping.