以地景指標與地形特性探討南化水庫崩塌地變遷分析

Analysis of Landslide Changes by Landscape Metric and Topographic Properties in Nanhua Reservoir Watershed.

張司璇(SSU-HSUAN 張司璇 CHANG)

指導教授 ： 江介倫

國立屏東科技大學/工學院/水土保持系所/碩士(2015年)

https://doi.org/10.6346/NPUST.2015.00028

摘要

臺灣因地理位置特性導致身具地質條件脆弱、風災頻繁的命運，近年來大型颱風事件侵襲次數增加，2009年更有莫拉克颱風極端降雨，使山區土砂災害頻傳，除造成生命財產威脅外，對水資源運用緊迫的南臺灣水庫，更是產生嚴重淤積，縮減庫容，影響未來水庫壽命及水資源調度的能力。有鑑於此，從防災觀點出發，深入了解崩塌特性並作合適崩塌治理策略評估則成水庫經營重要課題；故本研究以南化水庫為研究樣區，透過遙測影像技術搭配地理資訊系統，判釋2008年至2013年集水區崩塌分布，並採用數值地形模型與地景指標分析，探討崩塌特性與崩塌地景結構變化過程。研究結果顯示，崩塌地面積及數量與侵臺颱風降雨量有高度相關性，各年平均颱風降雨規模則對大型崩塌影響較為顯著，若該年颱風擾動頻繁，且遭遇大型降雨事件，則會使崩塌比增加，進而影響崩塌地恢復速率。而南化水庫集水區崩塌的地形特性多發生於於200-600m高程範圍的下邊坡，坡度多在50%~80%間(六級坡為主)，當極端事件發生時，崩塌發生的坡度範圍會更顯集中；受到山脈走向與降雨迎風位置影響，東向、東南向及南向坡是崩塌作用旺盛區域，應是整治關注之重點。另外，將各年崩塌依位置變遷的空間差異，區分為擴崩區、復育區及維持不變區三類，進而探討崩塌的地景特性。從面積指標變遷交叉分析，可知多數擴崩區復育僅需1年，從先復育後擴崩的轉變比顯示，2008年至2010年約25.27%，2009年至2011年約34.46%，2010年至2012年則驟降至7.39%，顯示莫拉克極端事件造成的崩塌破壞，需2到3年才漸趨穩定。形狀指標與聚集連接度指標顯示颱風強降雨會使各崩塌類型嵌塊體形狀趨於複雜且空間分布較為緊密，擴崩區崩塌嵌塊體會使旋轉半徑增加趨向帶狀發展。復育區崩塌地的常態化差異植生指標(NDVI)充分反映逐年前後期崩塌位置的植生恢復狀況，發現在連續強降雨颱風侵擾年及颱風影響小的穩定年，NDVI值變化最為劇烈，表示不僅在穩定年植生自然復育狀況良好，既使在高頻率的颱風侵擾下，環境仍然表現高度彈性的恢復力，故未來在水庫集水區管理經營的考量上，應加強對極端降雨事件後大型坡地崩塌的清查與整治，才得以盡可能減少土砂沖蝕量，降低水庫淤積的風險。

關鍵字

南化水庫 ； 崩塌 ； 地景指標 ； 植生復育

並列摘要

Because of the peculiar geographical location, Taiwan is frequently suffering from natural disasters. Recently, it was struck by more and more severe typhoons. For example, Morakot, a typhoon which struck Taiwan in 2009, brought extreme rainfall that resulted in landslide. The catastrophe led to the threats of life and people’s property, and caused limited water resources as a consequence of sediment. For these reasons, from the point of view of disaster management, people should realize landslide properties and tackle them properly to manage reservoir. Therefore, this study used the satellite image and geographic information system (GIS) to classify as the landslide in Nanhua Reservoir from 2008 to 2013. Moreover, the analysis of the changes in landslide properties and landscape structures was discussed with digital elevation model (DEM) and landscape metrics. The research shows the areas and numbers of landslide are closely related to rainfall. Extreme rainfall will contribute to the increase of landslide, making a slow vegetation recovery. Landslide in Nanhua Reservoir usually occur at an altitude of 200-600 meters, with a slope of 50% to 80%. Due to the direction of hillsides and rainfall, erosion mostly centered in east, south-east, and south. Furthermore, the landslide classification was determined by the spatial differentiation to three types: increase, reduce, and maintain. From analysis of class area index (CA), vegetation needs one year to recover; however, the landslide which caused by Morkot Typhoon recover vegetation between two and three years. Shape index and aggregation index indicated that the rainstorm will cause complicated shapes and tightened distribution. The type of landslide increase became long shapes by Area-weighted Mean Radius of Gyration(GYRATE_AM). The type of landslide reduce used the normalized difference vegetation index (NDVI) to reflect the vegetation recovery. Vegetation still could grow up during the typhoon season, but the severe typhoons made NDVI intense change that implied high resilience. In conclusion, people should deal with the large landslide caused by extreme rainfall that can decrease the risks of sediment.

並列關鍵字

Nanhua Reservoir ； landslide ； landscape metrics ； vegetation recovery

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