德基水庫從1974年建壩以來，缺乏有效的泥砂管理策略，長期下來，因泥砂淤積導致庫容逐漸損失，目前水庫淤積率約為25%，屬於中度淤積，加上氣候變遷日益嚴重，降水強度和泥砂量的增加會造成水庫淤積率上升，而關於水庫泥砂管理的文獻主要集中在工程方面，在經濟學方面則是寥寥無幾，故本研究將分析及探討不同泥砂策略的可行性並結合經濟面向，幫助決策者能在有限經費的限制之下，擬定最合宜的治理方案，創造出最大的效益。因此本研究使用RESCON2模式，設計不同泥砂管理策略的操作方案和在氣候變遷的影響下，瞭解其經濟效益及泥砂管理策略的效率對於水庫壽命的影響。另外為了確保在實施沖砂時是否能有效降低至指定水位，本研究建置德基水庫水文概念性模式模擬沖砂時的水位情況。
本研究使用自1976年到2016年的水庫幾何資訊、水砂條件、以及實際水庫日運轉紀錄等資料來建置德基水庫RESCON2模式，並進行沖砂、疏浚與繞庫排砂在不同方案下的模擬，包含調整沖砂時的水位、流量與持續時間、調整不同的年最大疏浚量、調整實施繞庫排砂的持續時間並搭配不同的排洪排砂比效率，模擬結果發現僅沖砂能使水庫水續且經濟結果最佳，在氣候變遷影響下亦是如此，且在水文概念模式的假設下得知需沖砂達90天以上才能將水位有效降低至指定水位；而疏浚效率看似高於繞庫排砂，實質上在疏浚的可行性仍有待討論，外加繞庫排砂的模擬結果為最保守值，其清淤量仍需靠操作時間及技術才能決定。另外越早實施排砂策略能使水庫壽命延長，經濟結果越高，但在繞庫排砂方面因折現率因素，造成越晚實施繞庫排砂的經濟結果較高。在模式中為使用隨著時間下降的折現率6%，折現率的選擇影響其經濟結果，需考慮經濟，工程，氣候變遷等問題，制定一個適當的折現率。

Since the Techi Reservoir was built in 1974, has no sediment management strategy. The reservoir has lost 25% of its storage capacity due to sedimentation. To find the most efficient sediment management strategy, it is important to incorporate economic analysis in order to compare the costs and benefits of different strategies. This study used the RESCON2 model to simulate reservoir life and economic benefits under different scenarios for three different strategies: flushing, dredging and bypass method, by calculating costs and simulating long-term effects in order to help decision-makers formulate the most appropriate management plans. The different scenarios included changing the implementation scheduling of each method, and parameters that affect the efficiency of the sediment management strategy. In addition, this study built a hydrological conceptual model to simulate how much time and what parameters are needed to bring the water level down to the level needed for flushing.
The RESCON2 simulation results show that only the flushing method will extend the reservoir’s life by more than 300 years. Flushing also resulted in the highest aggregate net present value, converted from the maximum water yield in the remaining storage capacity, which came out to a total value of about 3.2 billion US dollars. In addition, the hydrological conceptual model shows that a fixed water level of 1315m and a flow of 57cms, it will take at least 90 days to effectively reduce the water level to the specified level needed for flushing to occur. This means that flushing is feasible, but requires planning and preparation.The aggregate net present value of dredging and bypass are about 2.3 billion and 2 billion US dollars. Because the model results show that the amount of sediment able to be desilted by dredging is more than bypass, and the cost of dredging is significantly lower than bypass due to the high construction costs needed for bypass, the efficiency of dredging seems to be higher. However, this may not be the case in all scenarios. The simulation result for bypass is the more conservative than dredging as there are more factors which must be assumed. For instance, the amount of desilting possible by bypass is determined by the operation time and the technology used to discharge the sediment. Another aspect of this research that requires further discussion is the declining discount rate. This research used a declining discount rate of 6%, as recommended by the World Bank and Taiwan experts. But, it may be important to consider economics, hydraulic engineering, and climate change together to check that this is in fact an appropriate value.

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