HYDRAULIC ESTIMATION OF DISPERSION COEFFICIENT FOR STREAMS

Inclusion of longitudinal dispersion enhances realism in the assessmen t of transport in streams by accounting for contaminant mixing. Here w e revisit the problem of estimating the longitudinal dispersion coeffi cient D from readily measurable bulk hydraulic variables, which is use ful in applications. We develop and calibrate, through field testing, a predictor for the longitudinal dispersion coefficient for streams th at is structured after the fundamental formula of G. I. Taylor. Compar ison of predicted with observed values of D shows the new optimized fo rmula providing closer estimates than the established formula of Fisch er, with respect to both mean accuracy and deviations from the mean, a chieving in 14 of the 24 cases studied predictive accuracy of 0.5 less than or equal to D-observed/D-predicted less than or equal to 2.