動床模擬廢除直潭壩以改善屈尺及廣興地區淹水問題之研究

Morphodynamics Simulation on Zhitan Dam Removal to Improve Flooding Issue in Quchi and Guangsing Area

王柏崴(Bo-Wei Wang)

指導教授 ： 陳發林

國立臺灣大學/工學院/應用力學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201601678

摘要

台灣地區地勢變化劇烈加上豐枯季節明顯，為了蓄水之故，新店溪上共建了五座水壩，但水壩的存在阻斷水流自然流動迫使泥砂淤積於水庫中，上游底床受淤以及壩體回水作用導致河岸兩處居民在洪水時期容易受淹水影響。
翡翠水庫為因應民國101年蘇拉颱風而採取放流操作，造成下游河段直潭壩至粗坑壩之間的屈尺及廣興地區發生嚴重洪災，許多廣興地區居民對於直潭壩在颱洪時期的操作存有疑慮，懷疑是因直潭壩開啟閘門時間過慢或者閘門並無全開起，才導致廣興地區嚴重淹水，又在築高堤會破壞當地自然景觀的考量之下，建議直接廢除直潭壩，期許能解決颱洪時期的淹水問題，因此本研究主旨在藉由模擬探討廢除直潭壩後的水砂分布行為，並以模擬結果作為參考，討論拆壩後是否能解決廣興及屈尺地區的淹水問題，或是否能夠有效提升兩地區的洪水保護標準。
本研究主要分為兩部分：第一部分為參考國內外相關的拆壩文獻，了解拆壩後實際河川的水砂分布現象；第二部分則為運用數值模擬軟體分別進行定床模擬及動床模擬，模擬範圍在粗坑壩至思源橋之間，藉由兩模擬結果比較屈尺及廣興地區在拆壩前後的水位差異。
在各重現期下定量流模擬60小時的結果顯示2年及5年重現期下，廣興及屈尺地區的水位僅能降低數十公分，在10年以上重現期水位降低幅度始大於1公尺，但仍無法解決兩地區的淹水問題，而在以5年重現期下定量流模擬300小時的結果中，上游底床受更顯著的沖刷狀況下，廣興地區的淹水問題能完全被改善，屈尺地區的淹水深度亦大幅下降2公尺，最後在民國104年蘇迪勒颱風之歷線作為模擬的邊界條件下則發現，歷經單場蘇迪勒規模的颱風後，兩地區的水位高程沒有降低，而歷經六場的結果與以5年重現期定量流模擬60小時的結果相似。
由模擬結果知曉，拆壩後廣興及屈尺地區的底床在短期內並不會受到顯著改變，必須在不斷歷經大規模的颱洪事件之後，主深槽底床才能明顯受沖刷進而改善此二地區的洪災問題，而定量流與變量流在上游河段的沖淤位置一致，僅量級的不同，因此可以確定拆壩後的泥砂分布位置，以利政府單位疏浚。

關鍵字

廣興 ； 屈尺 ； 拆壩 ； 直潭壩 ； 動床模擬

並列摘要

In Taiwan, due to the special terrain with high gradient slope and large flow velocity, 5 dams were built on Xindian River for water conservation. However, the existence of dams would cause sediment accumulation in the reservoir. Sediment deposition occurs the area of cross-section of river channel in upstream decreases, which leads to the residents beside the river banks would be easily impacted by the flood.
In response to the Saola Typhoon in 2012, Jade Reservoir took releasing operation, which caused the Guangsing and Quchi area between Zhitan and Tskeng Dam were seriously impacted by flood disaster. Many residents in Guangsing area doubted that the gates of Zhitan dam had not be operated correctly during this typhoon event, so they proposed to remove the Zhitan Dam to resolve the flooding issues. Therefore, the main purpose of this research is to discuss the sediment distribution after removing the Zhitan Dam by using numerical simulation.
This research was conducted in two phases. The first phase was referring to scientific and technical literatures relevant to dam removal. The second phase was using numerical simulation software SRH-2D to simulate fixed-bed and mobile-bed conditions. The range of numerical simulation was between Tsukeng Dam and Si-Yuan Bridge.
In the conclusion, 60 hours simulation under 2 and 5-year return period with steady inflow cases show that the water elevation in Guangsing and Quchi area could only descend tens of centimeter, but the descent value would be higher than 1 meter under the steady inflow case of 10-year return period. However, the flooding issues still exist in those two areas. The result indicated that the flooding issue in Guangsing area could be completely improved and the water elevation in Quchi area would be lowers for two meters under 300 hours of 5-year return period steady flow simulation. Finally, we used Soudelor Typhoon inflow hydrograph as boundary condition to simulate the situation under unsteady inflow. We found that the water elevation of those two areas did not change after experience single Soudelor Typhoon, and after 7 soudelor Typhoon, the result was similar to 60 hours simulation under 5-year return period steady inflow case.

並列關鍵字

Zhitan Dam ； dam removal ； Guangsing ； Quchi ； mobile-bed simulation

參考文獻

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