圖書典藏及影音數位平台

石門水庫自民國52年5月開始蓄水迄今，截至113年12月止，總庫容之淤積率已達約34%。石門水庫肩負北部地區重要的水資源供給重任，為維護防洪安全及達成水庫永續發展等目標，進行既有設施改善並建置阿姆坪防淤隧道等工程，期望加強水庫防淤及排洪能力，加上以抽泥泵浦將淤積於庫區之淤泥抽取後暫置於水庫後池堰下游，俟颱風期水庫洩洪時，淤泥藉由洪水自然回歸下游河道後入海，可維持河川天然輸砂作用並減緩水庫淤積量。針對石門水庫下游大漢溪及淡水河河道之影響及變遷狀況，經濟部水利署北區水資源分署已於100~113年間陸續執行相關計畫之研究。本計畫期望在颱洪期間水庫進行排洪排砂操作時，能持續研究下游河道水質、生態及沖淤之變遷情形，並分析其與水庫運轉操作之關聯性，以釐清各界疑慮，預期將有助於累積相關生態背景資料及河道底床變化等資料，提供未來排洪排砂操作之參據，俾利推動石門水庫永續經營管理目標。本計畫主要以歷年及汛期前資料為基礎分析依據，今(114)年度於汛期前及樺加沙颱風後進行河道沖淤、水質及生態調查分析，並針對樺加沙颱風與1020豪雨事件進行全洪程濁度即時分析。本計畫另以數值模擬分析下游河道與河口沖淤變化，探討排洪排砂操作對下游河道沖淤之影響。各工作項目說明如下：河道沖淤調查分析：在大漢溪與淡水河主流選取5處(包含鳶山堰)進行影像比對分析，選取6處(包含阿姆坪防淤隧道出口)進行河道斷面測量，選取10處(包含阿姆坪防淤隧道沖淤池與後池堰下游河道放淤位置)進行河道底床質粒徑分析，在淡水河主流選取3處溼地進行溼地底質與高程變遷分析，並在颱洪事件時依據5處自動濁度監測站數據及水庫運轉資訊，即時分析整體泥砂運移狀況，以瞭解水文事件與水庫操作前後下游河道之變化情形。數值模擬分析：(1)石門水庫排砂對下游河道沖淤之影響探討：以民國104年蘇迪勒颱風(約為石門水庫Q10流量)與93年艾利颱風(約為石門水庫Q100流量)為案例，模擬石門水庫排砂之現況操作與僅排放清水情境，藉此探討河道有無受到石門水庫排砂影響對下游河道及河口沖淤變化之差異。(2)阿姆坪防淤隧道開啟配合潮汐操作之可行性探討：以民國113年凱米颱風(約為石門水庫Q2流量)為案例，調整阿姆坪隧道開啟時機，以探討阿姆坪防淤隧道開啟配合潮汐操作對河口沖淤之影響。水質及生態調查分析：於大漢溪與淡水河主流之城林橋、新海大橋、臺北橋、關渡大橋、挖子尾等5處進行水質調查暨河床底棲動物(含魚類)、底棲及浮游藻類等生態調查。此外，因文蛤為淡水河下游的重要經濟物種，其數量變動受到漁民關注，而蟹類則推測其數量與物種組成應能反應底床質粒徑變動情形，且較不受人為捕撈與放養影響，亦選定進行指標物種分析。綜合今年度(114年)汛期前及汛期中的調查與數值模擬結果，以及歷年調查分析結果，今年度歷經樺加沙颱風與1020豪雨事件，兩場事件雖於水庫集水區降雨有限，但為排出堆淤土砂仍開啟阿姆坪防淤隧道。隧道開啟後，中庄攔河堰至鳶山堰區間皆觀測到濁度高峰(樺加沙颱風期間中庄攔河堰最大值達2,833 NTU)，然而更往下游的新海大橋與臺北橋則無明顯濁度高峰出現。針對阿姆坪防淤隧道操作分析(截至今年底共6次)，下游濁度主要受颱風規模及是否形成異重流影響，防淤隧道並非影響關鍵。今年汛期中的河道測量結果與汛期前相比，淡水河下游段(T002至T029)主深槽呈現0.5~3公尺之沖淤變化，上游T034至T086斷面則無明顯變化。溼地部分，挖子尾、紅樹林與華江橋三處溼地之高程變化量極微(平均變化分別為-0.018公尺、0.010公尺與0.036公尺)，顯示近期濕地底床相對穩定。根據數值模擬結果，石門水庫若進行排砂操作，將使下游河道土砂量增加，惟河道整體底床變化仍受天然地形變動影響較大。若阿姆坪防淤隧道能於洪峰前2小時或與排洪隧道同時開啟，將有助於泥砂運移至較遠處落淤，使河口整體沖淤變化較小。結合歷年水域生態調查結果，颱風事件過後生物的豐度與物種數並無明確變化趨勢，顯示石門水庫操作並未對水域生物造成影響。

From 1963 to the end of 2024, the percentage of deposits to the total installed capacity of Shihmen Reservoir has been accounted for nearly 34%. In order to increase the lifespan of Shihmen Reservoir, the government has completed the desilting tunnel project of the hydroelectricity power plant and constructed the Amuping Desilting Tunnel. This project monitored and assessed the potential influences of sediment flushing on water quality, ecology, and hydrological characteristics of the lower reach. The goal was to analyze the correlation between these operations and provide data to support the sustainable management of the Shihmen Reservoir.This project referred to historical data and data in the dry season as the baseline, and conducted riverbed topography, water quality and ecological investigations twice this year, and analyzed the variation of riverbed landform by numerical modeling to explore the influences of sediment flushing on the lower reach. The details are explained as follows:Riverbed topographic investigations: Analyzed images at five locations along the Dahan River and Tamsui River main channels, measured cross-sections at six locations, and analyzed sediment particle size at ten locations (including the sedimentation pool of the Amuping Desilting Tunnel and downstream of the reservoir weir). Conducted wetland sediment and elevation change analysis at three locations. During flooding events, real-time data from five automated turbidity monitoring stations were used to analyze the changes in downstream river channels before and after hydrological events and reservoir operations.Numerical modelings: (1) Investigated the impact of sediment‐flushing operations at Shimen Reservoir on downstream riverbed erosion and deposition. Using Typhoon Soudelor in 2015 and Typhoon Aere in 2004 as case studies, the simulations compare the current sediment-flushing operations with a clear-water release scenario to examine whether and how sediment flushing influences downstream river channel and estuarine morphological changes. (2) Assessed the feasibility on coordinating the opening of the Amuping Desilting Tunnel with tidal conditions. Using Typhoon Kemi in 2024 as a case study, the timing of tunnel opening is adjusted to assess how tide-synchronized operations of the Amuping Desilting Tunnel may affect erosion and deposition processes at the estuary.Water quality and ecological investigations: Conducted water quality investigations at five locations along the Dahan River and Tamsui River main channels. Performed ecological surveys of riverbed benthic organisms (including fish), benthic and planktonic algae, and other ecological factors. Additionally, due to the economic significance of the freshwater clam in the downstream Tamsui River, its fluctuation is of concern to fishermen. Moreover, crab species are expected to reflect changes in sediment particle size and are less affected by human fishing and stocking activities. Therefore, the clam and crab were selected for indicator species analysis.Based on the surveys conducted before and during the 2025 flood season, numerical modeling results, and analyses from previous years, two rainfall events occurred this year. Although rainfall over the reservoir catchment during both events was limited, the Amuping Desilting Tunnel was operated to release accumulated sediments. After the tunnel was opened, turbidity peaks were observed along the reach with a maximum turbidity of 2,833 NTU recorded at the Zhongzhuang Weir during Typhoon Ragasa. In contrast, no significant turbidity peaks were observed further downstream. Analysis of the Amuping Desilting Tunnel operations (six operations in total up to the end of this year) indicates that downstream turbidity is mainly influenced by the scale of typhoon events and whether hyperpycnal flow forms, rather than by the tunnel operation itself. Comparisons of channel survey results during the flood season with those before the flood season show that the main channel in the downstream Tamsui River reach (T002 to T029) experienced erosion and deposition changes of approximately 0.5 to 3 meters, while no significant changes were observed in the upstream cross-sections from T034 to T086. For wetlands, elevation changes at the three investigated wetlands were minimal, indicating that the wetland beds have remained relatively stable in recent periods. Numerical simulation results further indicate that sediment flushing operations at Shihmen Reservoir would increase sediment loads in downstream channels; however, overall bed changes are still more strongly governed by natural geomorphic processes. If the Amuping Desilting Tunnel is operated two hours before the flood peak or simultaneously with the Tunnel Spillway, sediment transport to more distant deposition areas would be enhanced. Finally, when combined with long-term aquatic ecological survey results, no clear trends in changes in biological abundance or species richness were observed following typhoon events, indicating that Shihmen Reservoir operations have not caused discernible impacts on aquatic biota.