圖書典藏及影音數位平台

曾文水庫為台灣容量最大之水庫，亦為嘉南地區最主要之水源，兼具灌溉、給水、發電及防洪功能。該水庫位於嘉南平原之曾文溪主流上游，壩址位處台南縣與嘉義縣交界之柳籐潭，集水面積約481平方公里，滿水位面積約17.14平方公里，設計總容量7.127億立方公尺，以最低發電水位EL.171.0公尺為呆水位，水庫呆容量為1.172億立方公尺，有效容量則為5.955億立方公尺。 近年來，在納莉、海棠、泰利及莫拉克颱風等降下超大豪雨侵襲下，曾文水庫防洪能力已面臨氣候變遷的考驗。此外，曾文水庫興建時並未考慮庫底排砂設施，經統計，自民國62年4月蓄水以來至民國97年底，水庫的年平均淤積量約為465萬立方公尺，低於設計年平均入庫砂量561萬立方公尺。惟單就莫拉克颱風的侵襲，就為水庫帶來約九千萬立方公尺之淤積量，約為上述年平均淤積量之19.7倍，造成曾文水庫壩前庫床淤積達EL.179公尺，已無呆容量，目前累計淤積量(103年10月實測)則高達27,616萬立方公尺，年平均淤積量暴增為約665萬立方公尺，為設計年平均入庫砂量之118%。由於壩前庫床淤積已達EL.179公尺，遠高於永久河道放水道（以下簡稱PRO）進水口底部EL.153.37公尺及發電進水口中心高程EL.165公尺，已嚴重威脅PRO、電廠之正常運轉且水庫的有效容量，故曾文水庫永續經營及穩定供水因而受到嚴厲的考驗。 為減少曾文水庫淤積問題，經濟部水利署南區水資源局（以下簡稱本局）於102年3月發包「曾文水庫防淤隧道工程」（以下簡稱本工程），冀由本工程興建後進行汛期水力排砂，排除汛期時水庫的部分來砂量，以舒緩水庫取水營運之危機並延長水庫壽命。 本工程為「曾文南化烏山頭水庫治理及穩定南部地區供水計畫」項下之重要水庫更新改善工程，其結構安全性與操作功能正常與否，攸關其排砂效益之發揮，為妥慎複核本工程之執行期間之相關設計、施工及監測等紀錄資料與執行後續現地檢查等工作，本局擬依「水利建造物檢查及安全評估辦法」第十七條第一項規定，成立「曾文水庫防淤隧道工程計畫－使用前安全複核」委託技術服務計畫(以下稱本計畫)，冀由本計畫辦理之安全複核工作，確保本工程使用前之安全性與效能。

“Desilting tunnel of Zengwen Reservoir” is designed and built on the left shoulder of Zengwen Reservoir dam to supply the hydraulic desilting channel during rainy season. The major purpose is to reduce the operational crisis and extend the life of the Zengwen Reservoir. The main structures include elephant trunk steel pipe, inlet tunnel, gate and shaft, tunnel, plunge pool and outlet tunnel. The tunnel project was completed at November 28, 2017. According to the regulation of Hydraulic construction inspection and safety assessment rules, the first item of article 17, “The founder should make a comprehensive review of the detail design, test, construction, inspection and monitoring records during construction before use”, this report is submitted to ensure the safety and effectiveness of the tunnel before use. The item of safety review before use includes geology, earthquake, analysis of monitoring data and safety assessment of tunnel structures, operation and alarm systems, stability of slopes around desilting tunnel, other important facilities, etc. According to the results of comprehensive review, the desilting tunnel of Zengwen Reservoir is built in compliance with the original design requirements, the regulations of turnkey package requirements and contract specifications. It can provide predetermined functions and its facilities are safe. When the desilting tunnel put into operation, it will have the efficacy to reduce the operational crisis and extend the life of the Zengwen Reservoir.