Analysis of Two-Dimensional Mixing in Natural Streams Based on Transient Tracer Tests

To investigate the two-dimensional dispersion characteristics of the dissolved contaminant in natural rivers, tracer experiments were performed based on the instantaneous injection of Rhodamine WT solution into small- to medium-sized rivers in Korea. The relations between the dispersion coefficients and hydraulic and geometric variables of the river were analyzed in depth. The experimental results show that transverse dispersion coefficient tends to increase as the friction term, U/U*, and the channel aspect ratio, W/H, increase. The effect of the channel curvature on the rate of transverse mixing was found to be very distinct in that DT/HU* has a linear relation with UW/U*Rc, even though the slope of the fitted line in the plot of DT/HU* versus UW/U*Rc in a log-log scale was much smaller than the slope of the equation by Yotsukura and Sayre. The longitudinal dispersion coefficient also tends to increase as U/U* and W/H increase. However, DL is rather insensitive to the channel curvature. The values of the longitudinal dispersion coefficient from field studies are much higher than the theoretical value suggested by Elder. The observed longitudinal dispersion coefficient is one order of magnitude larger than Elder's coefficient, and DL/DT of this study ranges 26.6-332.