興建水庫得以蓄存水資源，卻也阻斷了河流的泥砂傳輸，導致庫區淤積量逐年提升，亦縮短水庫使用年限。為求現有水庫的永續運轉，水庫排砂已成為全球水庫正共同面對的議題。
在眾多水庫排砂方式中，空庫排砂為排砂效率最高的方式之一(Chaudry, 2014)，而峽谷型水庫又因地形條件較佳，可進一步提升排砂效率(Wang et al., 2020)，湖泊型水庫則因地勢較緩且庫區寬廣，須仰賴更好的操作以減少沖刷渠道外之庫區淤積問題，以維持排砂效率。
阿公店水庫為台灣目前唯一持續進行空庫排砂之水庫，亦為國際上少數採用空庫排砂之湖泊型水庫。為了解阿公店水庫排砂過程中，沖刷渠道形貌演變及庫區泥砂運移情形，本研究使用SRH-2D水理及動床模式進行模擬，並探討短期、長期沖刷渠道工程情境下之排砂效率。
研究成果顯示沖刷渠道可加速排除來自濁水溪之高濃度入流，降低泥砂落淤之可能，且事件過後濁水溪及沖刷渠道沿程普遍為侵蝕，顯示在沖刷渠道之協助下，仍可達通砂、清除庫區既有淤積之排砂目標。
本研究模擬成果顯示，事件期間庫區水位及事件起始水位越低，出流含砂濃度、排砂效率皆越高。但，若事件期間水位過高，無論是高入、出庫流量下，或短期、長期沖刷渠道工程情境，皆無法有效維持含砂濃度；若溢洪管閘門開啟時庫區水位過高，將降低事件初期空庫之影響，顯示事件起始水位、事件期間水位、溢洪管閘門開啟時之庫區水位等皆與排砂效率相關。
根據本研究模擬成果，若可將現行沖刷渠道斷面拓寬至40公尺、挖深至2公尺，即可於短期內有效提升排砂效率。長期而言，由於水庫分區排砂效率顯著高於沖刷渠道之幾何調整，仍建議規劃水庫分區，避免來自濁水溪之高濃度入流溢淹至旺萊溪側庫區。

Constructing reservoirs serves to store water resources, but it also interrupts the sediment transport in rivers, causing sedimentation and reduce of lifespan of reservoirs. For sustainable operation, sediment flushing has become an important issue.
Among various sediment flushing methods, empty flushing is one of the most efficient methods (Chaudry, 2014). In Taiwan, Agongdian Reservoir is currently the only reservoir implementing annual empty flushing, also one of the few lake-type reservoirs adopt it worldwide. Lake-type reservoirs, however, with their gentle slope and wide reservoir storage range, require careful operation to maintain effective sediment flushing.
The simulation result shows that the flushing channel can accelerate to remove high suspend sediment concentration (hereinafter referred to as SSC) inflow from Zhoushui River, reducing the likelihood of sediment deposition. Furthermore, erosion happens along the Zhoushui River and flushing channel, demonstrating that with the assistance of flushing channel, sedimentation can be removed successfully.
Simulation also shows that lower initial water level and the water level during flushing result in higher SSC and sediment release efficiency. Conversely, higher water level will weakness the benefits of high inflow, high outflow and flushing channel scenarios, making it difficult to maintain SSC of outflow. Opening spillway gates at high water level will also reduce the effect of empty in the beginning. It shows that sediment release efficiency is related to initial water level, water level during rainfall events and water level when the spill shaft opened.
According to our study, widening and deepening the flushing channel will effectively enhance sediment release efficiency in the short term. But in the long run, partition desilting is more effective than adjusting the geometry of flushing channel. We recommended to plan partition desilting and operations at low water levels to prevent the high SSC inflow flows into Wanglai River side of the reservoir.

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