Longitudinal Dispersion in Sinuous Channels

The longitudinal spreading of tracer solution and the distribution of velocity are investigated experimentally in a laboratory flume having a series of 13 uniform bends in alternating directions. Viewing the tracer cloud as a whole, the dispersion process behaves like a one-dimensional diffusion process, as in a straight channel. The dispersion coefficient is larger, and the initial convective period is shorter than in an equivalent straight channel. From the perspective of a single cross section, however, the process is periodic. The convective dispersion coefficient attains a maximum at about the middle of each bend, a minimum between bends, and lags the mean square velocity deviation by about a quarter of a bend. Analysis of the flume data together with available river data indicates that the dispersion coefficient tends to increase with increasing radius of curvature, and decrease with increasing bend length and depth.