不同時期地形資訊探討草嶺地區地形變遷之研究

Abstract

草嶺地區為台灣有名之大崩塌地，歷史上曾發生過四次大規模之崩塌，尤其1999年9月21日發生集集大地震時中部山區有多處崩塌。其中尤以雲林縣古坑鄉草嶺村附近之堀畓沓山所發生崩山之規模最大，其大量崩落土石阻斷了清水溪之水流，並在崩落區之上游形成堰塞湖（草嶺潭）。由於此堰塞湖可能會因某種因素而潰壩，並造成下游地區嚴重之土石災害，故曾造成ㄧ陣恐慌。倘能對其早期至今之地形變化進行了解，必能有益於對其現況之處理及未來再發生崩塌時處理決策之訂定。 本研究蒐集了國內外相關之研究資料，並以1930年繪製(1904年開始測量)之台灣堡圖及於1998年與1999年拍攝之航空像片，分別製作成數值高程模型(DEM)。接著進行自1930年至1999年的地形變遷分析，期能增加早期地形變化特性之了解，必能有助於對崩塌區地形變遷較完整之認知。經過平面校正後發現台灣堡圖中未變區地形之走向大致與1998年經正射之影像相符，且1998年較1930年的崩塌區增加三處，應為1941年與1979年兩次崩塌所造成。另外，河道之左岸向右岸偏移約360m，亦即河道明顯向右岸順向坡之基腳侵蝕，使岩層下端受到掘鑿作用失去支撐而形成自由端，經雨水之浸潤與地震之搖震而失去平衡，以致造成堀畓山持續發生崩塌至倒交山。由於兩個時期產生誤差之原因不少，必須經過日據時代平面及高程測量之誤差檢定與校正等步驟，方可做更精確的量化分析。

Tsaoling Landslide Area is celebrated for avalanche in Taiwan. There have had four times of serious collapses in history. Above all, the Chi-Chi Earthquake that occurred at September the 21-th of 1999, caused an especially number of collapse. At the Chi-Chi Earthquakes, the scale was great in Kuh-lum Mountain, in Gukeng Village of Yun-lin County. There were very much slid down earth mass and stone blocked on Ching-Shui Stream and formed a Tsaoling Lake. Because the barrier levee of the lake may breach due to breaking down for some causes and occur calamity and panic at the lower stream area. If we can investigate the landform change clearly it will help us to make a good policy for treating the mass of collapse. This study has gathered international paper about collapse, and gathered the ancient map of 1930 year then to build the DEM for analyzing the change of landform of Tsaoling Landslide Area during 1930 to 1999 for expecting we can understand the landform characteristic of nowadays landform and original landform. After plane-proof reading, we discovered that the unchanged area of the former map is similar to the landform of 1998. The three sites of newly collapsed of 1988 after 1930 was inferred from the collapsed at 1941 and 1979. The location of river moved approximately by 360m from left bank to right bank, and the bottom of the consequent slope of the rock stratum in right bank was eroded. It has formed a free end of the rock stratum in Kuh-lum Mountain and after the water eroding the rock stratum was unbalanced and then caused landslide for raining and earthquake. Owing to some errors for the two different times, plane and elevation check and adjustment must be introduced to perform a precise analysis.