Diffusion and Dispersion in Coastal Waters

Abstract

This paper presents the results of oceanographic drogue and current meter studies performed in the coastal waters of southern California. The purpose of the study was to evaluate, over diurnal periods, the transport and dispersing properties of the oceanographic currents at this location and relate them to extant theories of diffusion and dispersion in coastal waters. The measurements provide useful results concerning Lagrangian and Eulerian estimates of turbulent diffusivity. In particular, they show the importance of regarding diffusivity as an ensemble average property of the turbulent flow field, and that great care is necessary in applying the concept to single realization studies. The studies show that under some tide conditions significant negative diffusivities are possible. Furthermore, it is found that at this location coastal motions tend to be very coherent up to scales of 4–5 km, at which point they become rapidly dispersive. The results provide information of value to engineers concerned with the design of ocean disposal systems.