- 期刊
防淤隧道進水口高程影響排砂效率之研究
Study on the effect of desilting elevation for sediment desilting efficiency
摘要
霧社水庫截至2021年統計庫容淤積率約為75.22 %，壩前淤積高程已達977.52 m，因此興建防淤隧道作為水庫防淤策略之一實屬重要，然而防淤隧道進水口底檻高程的設計，除了需要考量排砂效益是否可達到預期規劃目標外，亦應符合施工可行性與考量長期營運操作。本研究根據模型相似定律，以不等比模型探討Q_2水文情境與防淤操作下，霧社水庫防淤隧道進水口底檻高程與排砂效率之影響關係。研究成果顯示入庫渾水抵達壩前時，渾水頭部依序抵達排洪隧道、發電進水口、防淤隧道及溢洪道平面位置，且根據Q_2（2年重現期距洪水）滯洪排砂（起始水位高程約為1,002 m）及洩降排砂（起始水位高程約為990 m）情境試驗結果顯示，入庫渾水從試驗上游邊界（約距離壩址5.4 km）運移至防淤隧道平均速度分別約為0.18 m/s及1.60 m/s，試驗結果亦顯示，防淤隧道排砂比在進水口底檻高程為960 m及975 m時，在Q_2滯洪排砂及Q_2洩降排砂情境下，差異分別為1.79 %及3.95 %；此外，防淤隧道進水口底檻高程越低受到阻塞風險越高，由試驗結果顯示，在設定水文條件Q_(10)（10年重現期距洪水）試驗情境下，防淤隧道進水口底檻高程969.6 m已完全被掩蓋，淤積面高程977.52 m約與現況相當，且約自距離壩址700 m至壩前有產生明顯沖刷渠道產生，寬約32 m左右，故建議興建防淤隧道進水口底檻高程以975 m較為適當。
並列摘要
The sedimentation rate of the Wushe Reservoir in 2020 is approximately 74.98%, and the sedimentation elevation in front of the dam has reached EL. 977 m. Therefore, constructing a desilting tunnel as one of the reservoir's desilting strategies is crucial. However, the desilting elevation of the desilting tunnel needs to consider the feasibility of construction and operation and whether the desilting sediment efficiency can meet the planned conditions and goals. Based on the model similarity law, this study uses a distorted model to explore the effectiveness of the elevation of the desilting tunnel on sediment desilting efficiency under different hydrological conditions and operations. The research results show that when the turbid water enters the reservoir, the head of the turbid water sequentially reaches the tunnel spillway, the power generation inlet, the desilting tunnel, and the spillway. According to the test results under the Q_2 (two-year return period) scenario of detention sluicing and drawdown flushing, the average transport speed of the turbid water is about 0.18 m/s and 1.60 m/s, respectively. The test results also show that under the Q_2 flood detention (initial water elevation is around EL. 1002m) and Q_2 drawdown flushing (initial water elevation is around EL. 990m) scenarios, the desilting efficiency difference of the desilting tunnel is 1.79% and 3.95% when the inlet bottom elevation is at EL. 960 m and EL. 975 m, respectively. However, the lower the elevation of the inlet bottom of the desilting tunnel, the higher the risk of blockage. Under the hydrological condition of the Q_(10) (ten-year return period) scenario, the top elevation of the desilting tunnel at EL. 969.6 m has been completely covered by sediment, and the deposition surface is about equivalent to the current elevation of EL. 977 m. Moreover, an eroded channel has been generated from about 700 m away from the dam site to the front of the dam, with a length of about 700 m and a width of about 32 m. Therefore, it is recommended to construct the desilting tunnel at an elevation of EL. 975m, which is more appropriate.