Probabilistic Analysis of Ocean Outfall Mixing Zones

Abstract

A methodology for ocean outfall mixing zone analysis is presented. It is based on a combination of four deterministic models for predicting hydrodynamic mixing behaviors of the discharged effluent, a continuous time domain simulation method, and an exceedance probability field concept. The approach provides a framework for evaluating mixing zones in compliance with receiving water criteria that are set in statistical terms. The approach was applied to the Hollywood outfall located off the east coast of South Florida. An exceedance probability field for effluent at a specified relative concentration of 0.021 was created. This field was applicable for determining the exceedance probability-based concentrations of any conservative pollutant at the regulatory mixing zone edge. A comparison of the probabilistic approach with the worst-case approach was made. The use of the worst-case approach was found to be too conservative for the subject outfall.