以CE-QUAL-W2模式模擬分析新山水庫優養化之原因

Simulation and Analyses of the Controlling Factors for the Eutrophic Condition of Shin-Shan Reservoir with CE-QUAL-W2

莊鎮維(Chen-Wei Chuang)

指導教授 ： 吳先琪

國立臺灣大學/工學院/環境工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.01474

摘要

位於基隆市的新山水庫為一個離槽水庫，提供基隆與大台北地區之用水。近年來新山水庫於夏季時常處於優養化狀態。本研究利用CE-QUAL-W2模式來模擬新山水庫之水質，及在夏季底層缺氧時，進行底層曝氣(hypolimnetic aeration)之效果，探討其對水庫優養化之影響及不同曝氣量造成水庫水體水理、水質之變化情形。本研究以2010年之實測資料做為模式參數校正的依據，而以2009年之資料作驗證。
分析結果顯示，以CE-QUAL-W2模式模擬新山水庫之水位、水溫等水理現象，其結果大致良好。而本研究模擬的水質項目有總磷、硝酸鹽及葉綠素a，其中總磷之模擬結果在冬季時會有偏高之情形，葉綠素a則是在夏季(8、9月份)時，會出現模擬值偏低之情形。整體而言，模擬結果尚可。
由模擬結果可看出，新山水庫在夏季底層曝氣後，水體中總磷濃度有明顯下降的趨勢，並隨著曝氣量的增加而有更顯著的改善。經曝氣過後，水體中硝酸鹽的濃度有些微的上升，但繼續增加曝氣量後，因水中氨氮已被用光，所以硝酸鹽濃度並未有太大改變。在經過底層曝氣過後，水中葉綠素a濃度並沒有明顯變化，推測原因為底層曝氣並無法明顯改善表水層之水質，因此對處在表水層的藻類而言，影響較小。
新山水庫在改變進流水總磷濃度後，水體中總磷及葉綠素a的濃度都有明顯的下降，顯示若對進流水營養鹽濃度進行控管，將可有效改善水庫水質，並且防止優養化的發生。

關鍵字

CE-QUAL-W2 ； 底層曝氣 ； 水質模式 ； 水庫優養化

並列摘要

Shin-Shan Reservoir located in Keelung city is an off-channel reservoir, which supplies water to Keelung and Taipei metropolitan area. In recent years, eutrophication occurred during summer time in Shin-Shan Reservoir. In this study, CE-QUAL-W2 model was used to simulate the effects of hypolimnetic aeration in Shin-Shan reservoir during summer and investigate the effects on the change of water quality under different intensity of hypolimnetic aeration. Model simulation was performed by using the data in 2010 as the basis of calibration for the model’s parameters, and used the measurement in 2009 for the verification of the model’s prediction.
The results of simulation showed good description of the hydrodynamic phenomena such as water levels and temperatures. In addition, the simulated results of the total phosphorus indicated overestimation of the total phosphorus during winter, while the model underestimation chlorophyll a during the summer (August to September). Overall, CE-QUAL-W2 modeling method provides a satisfactory closeness between simulated results and actual data in this reservoir.
Moreover, model analysis indicated a significant phosphorus concentration during summer with increase in hypolimnetic aeration. On the other hand, the concentration of nitrate in the water body increased slightly after a short period of hypolimnetic aeration due to the oxidation of ammonia to become nitrate, but reached a steady state once most of ammonia had been transformed. The concentration of chlorophyll a did not change significantly with the hypolimnetic aeration, presumably due to less direct impact of hypolimnetic aeration on the surface water quality.
Lastly, the simulation analyses show that by controlling the concentration of total phosphorus in the inflow, the concentration of total phosphorus and chlorophyll a would be significantly decreased in Shin-Shan Reservoir. In conclusion, controlling the quantity of nutrients in the inflow would be an effective way to improve reservoir’s water quality and preventing eutrophication from occuring.

並列關鍵字

CE-QUAL-W2 ； hypolimnetic aeration ； water quality model ； eutrophication

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