河川彎道污染傳輸之模擬分析

Abstract

本研究以二維深度平均水理及污染傳輸模式為基礎，植入二次流速度剖面函數，藉以模擬探討彎道效應對污染質傳輸的影響。首先針對彎道水理及污染質傳輸重要參數做因次分析，得到七個無因次參數，接著以此七個無因次參數做為案例設計之依據，並進行數值演算，演算結果對無因次參數作迴歸分析，得到二次流強度因子（SI）與長度因子（θ）為影響彎道污染傳輸之重要參數。分別在彎道區域與彎道後直線段區域，針對此二參數進行分析研究，得到此二區域最大濃度相對誤差與二次流強度因子及長度因子之關係圖，該關係圖可作為判斷彎道效應對污染傳輸影響程度之準則。最後，並藉由兩個天然河道案例之模擬，驗證該圖之正確性。

In this paper, the 2-D depth-averaged contaminant transport model incorporating with the secondary-current formulation was used to study the influence of the bend effect on the contaminant transport behavior in river bends. From the dimensional analysis, one obtained that the bend effect on the contaminant transport associates with seven independent dimensionless parameters. The regression analysis showed that the bend effect on the contaminant transport is mainly related to the relative strength of the secondary current and the relative length of the channel. The maximum relative difference on the contaminant concentration, obtained from the comparison of models with and without secondary-current formulations, is used to analyze the bend effect on the contaminant transport mechanism. Empirical relations between the maximum relative difference on the contaminant concentration, the relative strength of the secondary-current and the relative length of the channel for both channel-bend region and the straight region following the bend have been established. The field data reported by Lau and Krishnappan (1981) and Holley and Abraham (1973) are adopted herein to demonstrate the applicability and to verify the accuracy of the proposed relation.