ADVECTION-DIFFUSION PROCESSES AND RESIDENCE TIMES IN SEMIENCLOSED MARINE BASINS

This paper addresses the problem of estimating the residence times in a marine basin of a passive constituent released in the sea The disper sion process is described by an advection-diffusion model and the hydr odynamics is assumed to be known. We have performed the analysis of tw o different scenarios: (i) basins with unidirectional flows, in three space dimensions and under the rigid lid approximation, and (ii) basin s with flows forced by the tide, under the shallow water approximation . Let the random variable tau be defined as the time spent in the basi n by a particle released at a given point. The probability distributio n of tau is obtained from the solution of the advection-diffusion prob lem and the residence time of a particle is defined as the mean value of tau. Two different numerical approximations have been used to solve the continuous problem: the finite volume and Monte Carlo methods. Fo r both continuous and discrete formulations it is proved that if all t he particles eventually leave the basin, then the residence time has a finite value. We present here the results obtained for two study case s: a two-dimensional basin with a steady flow and a one-dimensional ch annel with flow induced by the tide. The results obtained by the finit e volume and Monte Carlo methods are in very good agreement for both s cenarios.