早期台灣為了減少水庫淤積，於水庫上游集水區建立多座防砂壩，隨著時間推移，防砂壩漸漸淤滿並影響其原本設計功能，同時因為壩體造成的河道不連續性產生生態衝擊的顧慮。本研究以七家灣溪為例，其中一號壩已於2011年改善完成，二號壩已於2004年自然潰壩，三、四號壩面臨淤滿以及壩體破損的情況。本研究為改善河道的連通性以及壩體淤滿而有潰壩之疑慮，以三號壩以及四號壩作為改善目標。
針對七家灣溪一號壩前人研究包括物理模型、後續監測以及數值模式的適用性等研究，此案例為台灣壩體改善之研究提供一個難得的經驗。故本研究透過現地調查蒐集三、四號壩資料，並參考前人研究成果，以SRH-2D模擬進行壩體改善後的影響，以不同改善方案、方式搭配颱風事件作為模擬情境，其中改善方案共分為(1)僅改善三號壩、(2)僅改善四號壩、(3)同時改善三、四號壩。並以對下游之衝擊、河防安全、生態棲地三項指標進行初步評估，後續再探討對河道之影響、串壩之間的交互影響。
由於本研究是以數值模式預測壩體改善後的變化，過往相關研究雖指出泥砂運移量推估之不確定性較高，但透過與一號壩案例的實際觀測值比較，兩者呈現相同趨勢，顯示模擬結果有其一定的參考性。
壩體改善須考慮各面向的影響，根據不同需求、目的會有不同之決策。本研究針對各情境的模擬結果有助於日後主管機關依其目的與需求去選擇三、四號壩壩體最合適之改善方案與方式。例如:基於對河道環境的衝擊與串壩間的影響，本研究建議改善四號壩1/2壩高為最佳改善方式。

In order to reduce the reservoir sedimentation in Taiwan, a number of check dams have been built in the upstream catchment. As time goes by, the check dams have gradually filled with sediment that affects the original design functions and because of the discontinuity of the channel caused by the check dam, there are concerns about ecological impact. The study takes Qijiawan Creek as an example, where, Dam NO.1 was removed in 2011, and Dam NO.2 was naturally broken in 2004. In order to improve the connectivity of the river, NO.3 and NO.4 dams are the focus of this study.
Previous studies of Qijiawan dam NO.1, including physical models, field survey, and the applicability of numerical models, provide a rare experience for the study of dam removal in Taiwan. Therefore, this research collected the relevant data of NO.3 and NO.4 dams by field survey and refered to previous research.By using SRH-2D to simulate the impact of dam removal, different improvement plans and methods combined with typhoon events were simulated. In addition, imulation results were further assessed by three indicators, i.e. downstream impact,river protection safety, ecological habitat. The impact on the river and the interactions between two dams were then discussed.
Although previous related studies have pointed out that the uncertainty of the estimating the sediment transport amount is high, the results obtained in this study showed the similar trend with the previous studies on NO.1 dam, indicating the applicability of the simulation results.
Dam removal must consider the impact of various aspects and then decisions can be made according to different needs and purposes. The simulation results of this study will help the authority as a decision support. For example, if the impact on the river environment and the impact between two dams were focused, this study suggests that the potential best improvement method is to removal the 1/2 height of the NO.4 dam.

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