Anomalous Diiusion in Bounded Temporally Irregular Ows

We investigate the longitudinal dispersion of passive tracers in a transversely bounded shear ow. The ow is assumed to be temporally irregular, but to possess smooth large scale spatial structure without signiicant small spatial scale motions. We show that, the existence of a region where the longitudinal velocity goes to zero linearly with 1 distance from the wall causes the tracers to \stick" to the walls. This results in a superdiiusive dispersion of the tracer. We analyze the growth of the variance and show that 2 (t) t with = 3=2. We verify this result by numerical simulation and compare the results from this model with experimental observations.