水庫浚渫導槽對排砂出口效率之影響

Impact of Dredged Guiding Channel on the Desilting Efficiency of Reservoir Outlets

艾斐拉(Nafeela Imtiyaz)

指導教授 ： 林國峰

共同指導教授 ： 賴進松(Jihn-Sung Lai)

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202102199

摘要

大壩和水庫為當今人類維持正常且穩定水資源供應的重要基礎設施，而水庫的維護與營運隨其扮演的功能特性而複雜程度不同，基本上，水庫可確保水、食物、能源及具備防洪功能，然而，水庫淤積問題對於水庫的水資源永續發展影響甚鉅，而水庫淤積的泥砂則主要來自於水庫集水區降下暴雨時，所夾帶的大量泥砂運移至水庫內所造成，若水庫進行排砂操作，則對下游河道產生生態問題，此外，若水庫缺水時，則可能造成農地無水可灌而休耕。為了處理水庫泥砂淤積的問題，可實施各種水庫泥砂管理策略，包含減少集水區的產砂量、減少入庫泥砂的沉積或是將淤積水庫的泥砂清除，其中，減少入庫泥砂的沉積為最有效益的防止泥砂淤積方式。因此，研究颱風豪雨時期，所引發的渾水流在水庫的運移型態，對於了解入庫泥砂淤積的行為非常重要，且可了解實施各種防淤策略組合或是實施前後的功效。本研究目的在於利用三維數值模 ANSYS-CFX，模擬颱風豪雨時期入庫渾水流之運移型態，並了解利用浚渫所形成之庫底導流槽，對於曾文水庫各出水工之排砂效率影響。由於曾文水庫為台灣蓄水庫容最大之水庫，且其受到莫拉克颱風影響後，水庫庫容已有約1/3受到泥砂淤積影響，因此本研究以曾文水庫為主要研究區域，且期望透過本研究之成果，能提供曾文水庫防淤策略之參考。根據本研究數值模擬分析水槽及現場案例之成果可知，所建立之三維數值模型，可準確模擬入庫渾水流之運移型態，因此其所模擬有無庫底導流槽之成果具備參考性，且庫底導流槽具備提升曾文水庫防淤隧道排砂之效益。

關鍵字

水庫淤積 ； 渾水流 ； 三維數值模式 ； 排砂效率 ； 防淤隧道

並列摘要

Dams and reservoirs are critical structures in the functioning of today’s world. Maintenance and the complexity of these structures is directly proportional to their size. One such associated challenge is the reservoir sedimentation. In some reservoirs this problem is caused by heavy rainfalls causing floods which bring huge amounts of turbidity currents into the reservoir. Reservoirs are vital to water infrastructures worldwide, ensuring water, food, and energy, and protection against floods. Sedimentation endangers the sustainable use of these reservoirs. Besides, the downstream impacts due to reservoir desilting operation have become an ecological issue, with the plough lands being the most at risk of becoming dormant when the reservoir volume decreases. To counteract reservoir sedimentation, different techniques, including sediment yield reduction, sediment routing, and sediment removal, may be implemented at dam sites. Of which, the sediment routing techniques have proven the most effective in reducing reservoir sedimentation and maintaining or re-establishing sediment continuity similar to pre-dam conditions. Studying the dynamics of approaching turbidity currents induced by heavy flooding during typhoon events is important for understanding the factors influencing sedimentation in the reservoir system and it plays a key role in the selection and implementation of management techniques in this system. These existing techniques can be modified and combined to build up a single efficient technique, which can be a potent approach in tackling the presented challenge. The aim of this study is to develop a better understanding of the turbidity current movement using a 3D numerical model namely ANSYS-CFX. And find the effectiveness of the dredging operation (guiding channel) on the venting efficiency. The Zengwen reservoir, which is one of the important water resources in Taiwan, has been affected by the problem of sedimentation, and thus it has been taken as a case study for this research. The research results can provide valuable operation information of reservoir desilting operation. According to numerical findings, the model is capable of predicting the turbidity current movement in the reservoir. The findings support the model's reliability in evaluating various desilting strategies. The results reveal that implementing the proposed technique to tackle the problem of sedimentation induced by typhoon events can be beneficial.

並列關鍵字

Reservoir sedimentation ； turbidity currents ； numerical modelling ； venting efficiency ； guiding channel

參考文獻

1. Wieland, M. Life-span of storage dams. 2010, 62, 32-35.

2. Wisser, D.; Frolking, S.; Hagen, S.; Bierkens, M.F.P. Beyond peak reservoir storage? A global estimate of declining water storage capacity in large reservoirs. Water Resources Research 2013, 49, 5732-5739.

3. Jodeau, M.; Chamoun, S.; Feng, J.; De Cesare, G.; Schleiss, A.J. Numerical Modeling of turbidity currents with Ansys CFX and Telemac 3D. E3S Web Conf. 2018, 40.

4. Morris, G.; Fan, J. Reservoir sedimentation handbook : design and management of dams, reservoirs, and watersheds for sustainable use. 1998.

5. Annandale, G.W.A.M., Gregory Karki, Pravin. Extending the Life of Reservoirs: Sustainable Sediment Management for Dams and Run-of-River Hydropower.