Estimating transverse mixing coefficients

The inaccuracy, and prohibitive field costs, involved in the evaluation of mixing coefficients severely limit the predictive capabilities of water quality models. This paper examines the traditional method of evaluating transverse mixing coefficients from field measurements and suggests a new simplified method of evaluation with significantly reduced data requirements. Results are presented from a series of laboratory experiments conducted on a large-scale test facility. Two planform configurations were tested—a straight and a meander channel. Both channels were of trapezoidal cross-section. Velocity measurements are presented together with the results of tracer studies conducted from continuous point source releases.Transverse mixing coefficients have been evaluated using both the traditional method of moments and the new method. The new method is shown to be a viable technique to obtain estimates of transverse mixing coefficients. The results highlight the impact of planform curvature on the rate of transverse mixing. The longitudinal location of a release with respect to a curvature is shown to be critical to the rate of transverse mixing.