水質處理型滯洪溼地之最佳化設計研究

Abstract

水質處理型滯洪溼地（Treatment Detention Wetland）為於滯洪池內加入表面流人工溼地配置，而成為複合式設施；其目的為於汛期具有滯洪功能，而於非汛期保有水質處理功能。而根據國內滯洪案例可以發現，台灣的滯洪池中水深幾乎都大於1.5m；然而，表面流人工溼地設計的水深範圍通常介於0.15-0.6m間，由此可知，當一個人工溼地擁有了滯洪池所設計之較高水深後，其水質處理功能必定存在著矛盾及妥協之處，因此水深將會是尋求同時滿足滯洪與水質處理兩種不同功能需求的最重要參數。 本研究利用TABS-2數值模式中之水理（RMA2）及水質（RMA4）模組進行模擬示蹤劑實驗，用以推估水力效率λ與汙染物移除效率，且於本研究中定義一個汙染物移除的量化指標–汙染物移除有效時間比et，使得水力效率對於汙染物移除的影響能夠加以量化。由模擬結果發現：水深由0.1增加至2.5m時，隨著水深的增加，水力效率從0.86下降至0.15；而BOD、ammonia、nitrate之移除有效時間比et也隨著水力效率下降而下降，亦即當水力效率減低時，汙染物之移除與理論移除效率差異也越多，故溼地中若有較高之水力效率，則對於汙染物移除而言，將會更符合預期之移除率。此外，本研究也利用迴歸分析，提出水力效率λ與汙染物移除有效時間比et關係式，其可作為實際設計參考。 最後，本研究綜合模擬結果，提出一個水質處理型滯洪溼地最佳化設計評估流程，以供後續設計者，能夠利用此設計流程，在滯洪池與表面流人工溼地兩者的衝突點上，找到一個平衡，進而設計一個最佳化之水質處理型人工溼地；同時本研究也以「嘉義沿海地區國土復育及永續發展規劃」所擬定的東石示範區，作為案例分析，以示範如何將這套最佳化設計流程實際運用於現地規劃中。

Treatment Detention Wetland means adding the FWS (free water surface) wetland into the detention pond. The function of Treatment Detention Wetland is to provide detention volume in the flood period and waste water treatment in ordinary days. Nevertheless, the designs of the detention pond and the FWS wetland are different. Take Taiwan for an example, the design of water depth is always over 1.5 - meters in Taiwan. According to EPA manual (2000), however, the range of water depth in the FWS wetland is 0.15-0.6 meters. As a result, the water depth lays a crucial role in Treatment Detention Wetland for seeking of satisfying both detention function and waste water treatment function. When the depth of the FWS wetland is as higher as the designing of the detention pond, there must exist some contradictions in Hydraulic efficiency, λ , and the pollution removal rates. A horizontal two dimensional model, TABS-2, was employed in this study to simulate the tracer tests for evaluating hydraulic efficiency, λ and the pollution–BOD, ammonia, and nitrate–removal rates based on Reed et al. (1995) with the simulated RTD (residence time distribution). Besides, this study defines a index, Effective Treatment Time Ratio–et ,to quantify the effective treatment time for pollution removing. The results demonstrate that when the water depth rises from 0.1 to 2.5 meters, the RTD are divergent, the effective volume rate, ev, is only half remain in 2.5-meter-depth and the hydraulic efficiency, λ, decrease from 0.86 to 0.15. Beside, the Effective Treatment Time Ratio–et decreases as the water depth elevated. Therefore, the difference of the pollution removal rates between the actual-situations and the theory-situations is higher due to the declined hydraulic efficiency, λ. This study integrates the result of modeling to bring up an optimal designing procedure for Treatment – Detention – Wetland – designing. Therefore, the follow-up designers could refer to this procedure to strike the optimal designing. By the way, this study also analyzes a case drew up by the project, Master Planning for Environmental Restoration and Sustainable Revitalization in Chiayi Coast Region, to demonstrate how to apply the procedure.