Reaeration Coefficient Estimate: New Parameter for Predictive Equations

Abstract

The reaeration coefficient (K _a) is an essential parameter to predict the dissolved-oxygen concentration in different aquatic ecosystems. The techniques applied to K _a estimates require considerable efforts, since measuring this coefficient is a laborious and expensive task. Thus, the use of predictive equations wherein K _a is found through hydraulic flow parameters is common. However, the available prediction equations lead to estimates often different from each other. A new predictive equation is addressed in the present study. The insertion of a dimensionless number resulting from the relation between the RMS (Root Mean Square) of the free-surface vertical velocity and the surface flow velocity is the great innovation of the study. The reaeration experiments and the surface vertical velocity mapping were performed in a circular hydraulic channel. The flow velocity varied from 0.25 to 0.64 m s⁻¹, and depth varied from 0.09 to 0.15 m. The new equation led to more accurate results than the equations based on traditional hydraulic parameters such as the Reynolds and Froude numbers, mainly when it comes to K _a values higher than 40 day⁻¹. The sensitivity analysis has shown that the new dimensionless number is the most sensitive parameter of the herein proposed predictive equation and that the influence from the Reynolds and Froude numbers on K _a weakens as turbulence gets more intense.

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