石門水庫繞庫排砂策略之研究

Abstract

石門水庫為北台灣供水的要角，如今，石門水庫淤積情況日益嚴重，水庫有效地執行防洪防淤策略成為當前最重要的課題。近年來，石門水庫針對繞庫排砂策略進行多項研究，目前已有三項規劃案：C1(延伸管)案(大灣坪)、D2修改案(阿姆坪)與C1(延伸管)+D2修改案最有可能執行，三項規劃案之功能分別為排水排砂、清水沖淤及兩案聯合操作。本研究利用一維動床模式模擬石門水庫進行繞庫排砂策略，以了解考慮繞庫排砂策略前後，對於石門水庫之底床變化及既有各防淤設施之影響。 由本研究模擬結果可知，防洪防淤隧道之下游斷面，底床沖淤量才會改變；當防洪防淤隧道排出流量越高，對下游各防淤設施之排砂情況越顯著，考慮C1(延伸管)案、D2修改案與C1(延伸管)+D2修改案後，下游各防淤設施之排砂比分別減少12.54%、6.26%、11.61%，C1(延伸管)案改善效果最為明顯，其次為C1(延伸管)+D2修改案，最小為D2修改案。

Shimen Reservoir with the function of water supply contributes to the north of Taiwan enormously. Nowadays, the problem of sediment deposition in Shimen Reservoir is more and more seriously. It becomes more important to deal with the deposition efficiently. Recently, there have been many research about sediment bypassing in Shimen Reservoir. There are three alternative cases about sediment bypassing, which are C1 case(with extension tube in Dawanping), D2 modified case(in Amouping) and C1(with extension tube)+D2 modified case. The functions of these cases which are drainage and desilting on C1 case, only drainage on D2 case, and joint operation of C1and D2 case. This study simulates sedimentation of Shimen Reservoir before and after with sediment bypassing operation with one-dimensional mobile mode tool in order to comprehend that the erosion and deposition of bed changes and the desilting efficiency of outlets. From the simulation results in this study, we can know that the erosion and deposition in the reservoir occur downstream of the bypassing tunnel. The more water discharge from sediment bypassing tunnel, the less desilting efficiency of outlets will be improve. After considering the three cases, the reductions of sediment release efficiency of existing outlets are 12.54%, 6.26%, and 11.61%, respectively. The improvement of C1case (with extension tube) is most obvious, followed by C1(with extension tube)+D2 modified case and D2 modified case.