以現地分析及實驗解釋巴陵壩附近之地貌變化

Abstract

本論文以實驗配合現地資料探討巴陵壩潰壩後對河川地貌的影響，並且將實驗結果與現地資料做定性分析。從歷史現地資料可知，從潰壩前2003年至潰壩後2008年間，大漢溪水面線在巴陵壩上游段有下切的趨勢，而在下游段則有堆積的情況。潰壩前大漢溪與支流三光溪交會處在潰壩後的測量中著實有向下切且往下游移動的趨勢。而從實驗中可得，上游泥砂往下游結構物堆積的過程與主支流交界處往下游運移的經過。在現地資料與實驗的驗證後得知，淤滿的巴陵壩在壩體毀壞後，其沉積物隨著河水的流動被帶到下游堆積；相同地，攔砂壩上游的主支流交會位置也隨著潰壩、沉積物移動往下切並往下游方向變動。利用簡化的小尺度實驗，可以提供未來河川地貌變化的模擬預測。

River response to the construction and failure of a dam is examined in the present thesis using a combination of laboratory experiments and field data. The field case considered is the Balin check dam, constructed in 1977 across the upper TaHan River, which failed in 2007 during Typhoon Wipha. A special characteristic of Balin Dam is that it is located less then 2 km downstream of an important confluence, the junction of SanGuang River with TaHan River. To understand the river and confluence evolution from 1977 to 2008, we collected field data from various sources and carried out a new survey of the river and terrace profiles in December 2008. The comparison of historic and newly surveyed data before and after the dam breach documents a severe incision of accumulated deposits upstream of the dam, moderate aggradation downstream, and a dramatic incision and downstream migration of the confluence junction. It is found that these key features of the river and confluence response can be reproduced by simple small- scale laboratory experiments.