防砂壩移除對河床變遷影響之研究－以巴陵壩為例

The Influence to Channel Transition of Dam Removal：A Case Study of Baling Dam

10.6342/NTU.2009.01148

林欣怡

巴陵壩 ； 壩體移除 ； 河床穩定性指標 ； 棲地適合度指數 ； Baling dam ； dam removal ； riverbed stability index ； habitat suitability index (HSI)

國立臺灣大學土木工程學系學位論文

2009年

碩士

李鴻源

繁體中文

近年來基於結構安全與環境生態等考量，壩體移除開始成為熱門的議題，在國外已有許多利用拆壩而成功復育河川生態的經驗，在台灣，則仍屬於新興先導型研究。而在民國96年9月18日大漢溪巴陵壩發生潰壩事件，提供了一個極為難得之研究素材，因此，本研究擬定巴陵壩上、下游各5公里之研究範圍進行動床輸砂演算模擬，採用擬似二維水理輸砂演算模式NETSTARS模式，並根據模擬結果探討壩體移除後對河床變遷以及魚類棲地之影響。 另以動床模擬結果計算河床穩定性指標（K），發現巴陵壩潰壩（可視為壩體一次拆除）2年後河床可達到穩定平衡，若將壩體分兩次拆除，則河床約4年可達到穩定平衡狀態，且後者達到平衡之K值較大，表示其河床較前者更為穩定。不論採用何種拆壩方案，河床最終達到平衡狀態的K值約介於(1.4∼2)x104。 另外，二次拆除的間隔時間長短並非是造成日後河床演變差異的主要原因，而是拆除間隔期間是否有發生颱洪事件，故建議在工程實務上，儘量選擇在枯水期時進行壩體分次拆除作業。 本研究透過統計檢定分析探討拆壩對於魚類棲地造成之變化，不論潰壩前亦或是潰壩後以及假設壩體分兩次拆除的情形下，鯉科、鰕虎科、平鰭鰍科之魚類棲地適合度指數（HSI）皆無明顯的變化。但可以確定的是，在壩體拆除後，魚群便能順利洄游以及擴大其生存棲息的環境，避免近親交配帶來之危險，故在壩體移除之後，要如何進行棲地改善或是棲地重建，以營造出適合魚類生存的棲地環境，係未來研究的重要方向。

Based on structure safety and environmental & ecological consideration, dam removal becomes a hot public topic in recent years. And there are many practical experiences of dam removal in the world. In Taiwan, this is still a new issue to hydraulic research. However, in 18 September 2007, Baling dam in Tahen River was broken suddenly in the afternoon. This event provides a great chance to understand dam removal. So, this study will execute mobile-bed sediment transport numerical calculation and simulation to the upper and below 5 km of Baling dam and use NETSTARS which is a quasi-two-dimensional model to study the effect to riverbed and fish habitat after dam removal. After finishing upper numerical calculation and simulation, this study can get a riverbed stability index (K). Also it found that if Baling dam broke (it seems like removing it once for all), the riverbed takes 2 years to reach stable and balance status; but under the assumption of removing the dam for two steps, it takes 4 years. And when we remove the dam for two steps, its K-value is larger than we remove it one for all. In the end, this study finds that no matter how we remove the dam, K-value is always between (1.4∼2)x104. Besides, this study can know that different time-interval of removing the dam is not the major reason to cause the different riverbed variation. Actually, the most important factor is that if there’s a flood in the middle of 2 dam-removing steps. Therefore, to engineering practice, it’s better to choose drought period to remove the dam. In this research, this study also uses statistic test analysis to find the effect to fish habitat after removing dam. No matter it’s before dam-breaking, after dam-breaking, or we remove it for two steps, there is no obvious effect to Habitat Suitability Index (HSI) of Cyprinidae, Gobiidae, and Homalopteridae. But one thing is sure that after dam removal, the habitat and migration area of fish will increase. Also they can avoid the crisis of incest breeding. So, how to amend the habitat and create an environment that is suitable to fish is the first priority work in the future.

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