Comparison between Dispersion Coefficients Estimated from a Tracer Study and ADCP Measurements

We evaluate the use of river velocity and bathymetry data measured with an acoustic Doppler current profiler (ADCP) to estimate the longitudinal dispersion coefficient K. Whenever mixing is controlled by shear dispersion, the dispersion coefficient can be estimated from a theoretical formula that relies on velocity measurements in a cross section. The relative ease and detail with which ADCPs measure velocities allows the dispersion coefficient to be estimated with greater frequency and spatial coverage in U.S. rivers. We conducted simultaneous ADCP and tracer measurements in the Kissimmee River in South Florida under bankfull threshold conditions. The ADCP method underestimates the dispersion coefficient obtained from the tracer study by about 40%. Flow in side channels and over part of the river floodplains likely led to dispersion of the dye cloud that the shear dispersion mechanism does not take into account.