以地景指數探討高屏溪流域崩塌地之時序變遷

Time series change of landslide based on landscape metrics in Kaoping river basin

旗山、荖濃溪事業區屬高屏溪上游集水區之國有林班地，其為2009年莫拉克颱風重創之地區，林地崩塌災害嚴重，而崩塌災害前後之植生覆蓋變遷為集水區治理的重要工作。遙測衛星影像具有固定時間、大範圍取得地面資料之能力，可監測崩塌地分布情況及植生復育狀態。本研究以 2000年～2015年Landsat 7衛星影像作為研究材料，利用地理資訊系統（Geographic Information Systems, GIS），以人工數化取得各年度崩塌地圖層，並將崩塌地分類成維持不變型、植生恢復型、新增型及擴崩型，分析歷年各類型崩塌地之分布與植生自然恢復狀況，並藉地景指標探討高屏溪流域上游集水區崩塌地景結構之變異。由崩塌地之地景變遷分析可知，維持不變型崩塌地屬於破碎化地景，且地質結構不穩定，造成風災害後發生更多的擴崩地；新增型崩塌地主要受莫拉克颱風侵襲而生成，原因在於集中且強度降雨，使得地表土壤無法承受外來的重力，產生崩塌；植生恢復型在各年度恢復情形雖然良好，但恢復面積遠不及新崩塌面積。整體而言，高屏溪流域之崩塌地，隨時間的演變更趨分散與破碎，致使高屏溪流域之森林地景結構受到嚴重破壞。 Chishan and Lennon river working circle located on the national forest land in the Kaoping river basin was landslide greatly damaged by 2009 Morakot typhoon and to understand the land cover change of landslide before and after typhoon were important tasks of watershed management. However, satellite images enable the monitoring of wide range distribution of landslides. This study acquires the remote sensing images of Landsat 7 from the year 2000-2015 as materials. By digitizing spatial distribution and evolution of landslide via Geographic Information Systems (GIS) that could be divided into four types, namely are unchanged, recovery, appending and expanding. By utilization of landscape metrics to analyze the distribution of landslide vegetation recovery over the years, the results of landscape metrics showed that the unchanged-type tend to be fragmented and geologically unstable, which leads to frequent natural disasters and caused the existing landslide area to expand. The appending-type was mostly triggered by the Morakot typhoon, because heavy rainfalls falling on the ground surface, makes surface objects unable to stand fi rmly. The recovery-type recovers gradually; however, the area of landslide formation is signifi cantly faster than the area of recovery. Overall, the landslides of Kaoping basin are scattered and fragmented over time, which leads to heavily damaged forest landscape structure in Kaoping basin.