Measurement of Effective Saturation Concentration for Gas Transfer

Abstract

Bubbles entrained in the plunge pools of hydraulic structures are subjected to the hydrostatic pressure of the water column. The hydrostatic pressure increases the saturation concentration of gases within the bubbles and correspondingly alters the rates of gas transfer. An “effective saturation concentration” is introduced to account for the elevated pressure within the bubbles. The effective saturation concentration must be incorporated into gas-transfer calculations to accurately predict downstream concentrations of dissolved gases. A method of measuring the effective saturation concentration from simultaneous measurements of dissolved oxygen and methane is presented. The method is verified through similar measurements of dissolved nitrogen and methane. Applications demonstrate the use of the effective saturation concentration in the prediction of dissolved-gas levels downstream of hydraulic structures and the use of dissolved-gas measurements in the determination of the effective saturation concentration.