ESTIMATION OF VISITATION FREQUENCY OF SEA OUTFALL PLUMES

A methodology is presented to estimate the visitation frequency of sea outfall plumes; it consists basically of, plume centreline simulation and contaminant concentration field simulation. Plume centreline simu lation is performed by numerically tracking marked particles released continuously from an outfall diffuser, provided that current fields ar e known either from current meter data or numerical modelling. The con taminant concentration field at any time is estimated from a determini stic diffusion model which applies to plume segments along the centrel ine at that time. The centreline and concentration field simulations a re continued over time (known as simulation time); visitation frequenc y at any point is obtained by accumulating the time interval during wh ich the concentration at this point exceeds a specified value and from the ratio of the accumulated time to the simulation time. The method presented was applied to a case study of the proposed Heishijiao Bay O utfall, Dalian, China. In this case study, total coliform was taken as a pollution indicator in the estimation of visitation frequency. A co mparison was also made of our method with Churchill's plume simulation method; good agreement between two methods was achieved.