巴陵壩潰壩後河床形貌變遷行為之研究

A Study of Riverbed Morphology due to Barlin Dam Break

李聖文(Sheng-Wen Lee)

指導教授 ： 李鴻源

國立臺灣大學/工學院/土木工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01581

摘要

台灣位處於雨量豐沛及地震頻繁的地區，且山多坡陡又地質脆弱，每當颱風過境或豪雨來襲，常促使河水挾帶大量泥砂進入水庫，減少水庫壽命，淡水河上游的石門水庫為了攔阻來自上游之泥砂，於集水區內興建120餘座攔砂壩，其中巴陵壩位於石門水庫上游35公里之大漢溪主流上，壩高38公尺，攔砂總容量為1047萬立方公尺。壩體因長期侵蝕，於民國96年9月18~19日韋帕颱風來襲期間，壩體不堪負荷而發生潰壩，成為國內首座大型攔砂壩之崩壞案例，原先積蓄於壩體上方之土砂隨著潰壩的衝擊而被帶向下游，上游河床因此產生向源侵蝕，下游則隨泥砂增多而淤高，顯著影響壩上、下游各5公里之河段範圍。
巴陵攔砂壩潰壩後首次地形測量施作時間為96年12月，對於潰壩後四個月這段期間地形的變化探討，本研究利用數值模式(NETSTARS)進行輸砂模擬，並搭配穩定指標判斷模式輸出是否已達到穩定，結果發現潰壩後河床變化最劇烈的時期為潰後400小時，約13天的時間。此外，亦根據地貌學沖淤理論推導出對流擴散方程式，選用有限差分法求解以模擬和探討河床縱剖面之變化，因床形變化受流量與時間影響，所以利用假設時間τ將兩因素整合以便分析。由模擬結果可推論潰壩後上游向源侵蝕行為與假設時間τ呈冪次關係，下游淤積行為的擴展範圍與假設時間τ之關係亦是。此外，在下游河段亦發現到泥沙在潰壩後會短暫淤積於壩體下游附近，隨後再經由水流帶往下游的現象。經由設計案例之結果可推論不管是否有洪水影響，河床的變化趨勢與行為皆相同，僅有河床變化速度快慢之差異。

關鍵字

潰壩 ； NETSTARS ； 對流擴散方程式 ； 有限差分法 ； 向源侵蝕 ； 穩定指標

並列摘要

On September 18, 2007, Barlin Dam, a 38-meter-high dam built in 1977 in Shihmen reservoir collapsed, due to foundation damage and flood impact. After Barlin dam broke, sediment stored in the reservoir was flushed down to the river channel, and the downstream channel was expected to undergo major change in morphology. This event provided a rare chance to investigate and to understand riverbed adjustment after the dam collapsed. In this paper, we will focus on simulating stream profile evolution, discussing the head-cutting and deposition behavior. The quasi-two-dimensional model (NETSTARS) was employed to simulate reservoir and river channel responses after Barlin dam collapsed. Due to the fact that the variation of flow situation and landform was very severe, the output of the model would be shaken. In order to make the output more meaningful, we chose a stability index to evaluate the output and observe riverbed stability. In addition, numerical solution from advection diffusion equation was developed to model the river profile evolution hourly after Barlin dam broke. For the purpose of evaluating the head-cutting behavior and downstream deposition transportation behavior, it is an adopted way to observe the motion of knickpoint (or erosion threshold position) and deposition threshold position. Simulated longitudinal profiles of the thalweg after Barlin dam collapsed finally suggested that head-cutting and deposition behavior is a power law distribution.

並列關鍵字

Dam break ； NETSTARS ； Advection diffusion equation ； Finite difference method ； head-cutting ； stability index

參考文獻

18. 王瀅婷(2010)，「巴陵壩潰壩後對上游河床變遷影響之研究」，國立台灣大學土木工程學研究所碩士論文。

19. 台灣大學(2009)，「石門水庫集水區泥砂推估與處置綜合評析計畫」，北區水資源局。

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