大安溪峽谷河床高程變異情況之研究

大安溪峽谷是由於1999年的集集大地震（ML 7.3）造成東勢背斜構造抬升，河流產生回春作用，陸續的降雨及颱風增加河流下切作用，使此處逐漸於2008年形成完整的峽谷地形。本研究主要利用八個時期的地面光達資料製作的1 m解析度DEM配合降雨及河川水位等水文資訊，探討大安溪峽谷於2009年至2013年間的河床高程變異情況。研究顯示在大量降雨之後河床高程會有顯著提升，應為土石堆積物造成，而在河川水位上升之後，由於河流沖刷搬運土石使得河床高程又會有些許下降。整體而言，在2010年7月後峽谷內的河床高程測量結果皆較2009年10月來的提升，顯示大安溪於峽谷段的沖刷及堆積情況強烈，且河川下切作用已趨緩。

關鍵字

大安溪峽谷；光達；高程；降雨

並列摘要

The Daan Gorge was formed by the Chi-Chi earthquake (ML 7.3) in 1999. The riverbed has since uplifted where it crosses the Dongshi Anticline, producing a rejuvenation effect. Both rainfall and typhoons have increased the erosion rate, establishing the gorge terrain by 2008. This study used eight periods of 1 m resolution digital elevation model produced by terrestrial LiDAR data, and combined these with hydraulic information, such as rainfall and river levels. These data were used to analyze the change in elevation of the gorge section of the riverbed between 2009 and 2013. It was shown that the riverbed elevation increased significantly over this period, probably due to large amounts of sediment being deposited following heavy rainfall. However, the elevation relatively went down when the river level rose due to increased riverbed erosion. Overall, the riverbed elevation at the gorge section was higher after July 2010 than it was in October 2009. This suggests that a lot of eroded material had been deposited in the gorge section. It further indicates a possibility that the river down-cut process was slowing.