Uncertainty analysis of ocean outfalls

Abstract

Variability and uncertainty are inherent in an ocean outfall system and will cause variation in estimated initial dilution and bacterial concentration at areas of interest near the discharge. Uncertainty analysis is therefore useful in evaluating the likely performance of the outfall and in determining if it will comply with relevant government regulations. This paper identifies the uncertainty in outfall design parameters for an outfall involving a single, horizontal, round buoyant jet discharging into an unstratified seawater environment. A case study based on data from the Spaniard's Bay outfall in Newfoundland, and using a Monte Carlo simulation, is presented and compared with some, limited, site data that are available. It is shown that the analysis adequately describes the probabilistic nature of the initial dilution and bacterial concentration and that it would be useful for practical design purposes.Key words: bacterial pollution, buoyant jet, initial dilution, Monte Carlo simulations, probabilistic design, sewage discharge, ocean outfalls, uncertainty analysis, water quality standard.