Predictions of effluent fields discharged into Royal Roads
A method is devised to predict the "worst case" shoreline concentrations in the effluent field discharged from a submerged ocean outfall. Three phases in the dilution process are recognized and are combined into an empirical equation: initial dilution, turbulent diffusion, and decay. Readily obtainable environmental parameters such as wind speed and direction frequency distributions, water current speed and direction frequency distributions, and the density stratification frequency distribution are employed to predict the "worst case" concentrations and their probabilities at selected shoreline locations. The technique is applied to the Royal Roads area, a coastal embayment in the Greater Victoria area in which a sewer outfall already exists and a second outfall is proposed. In order to predict the median shoreline coliform counts for critical locations, the "worst case" values are fitted to a lognormal distribution with a standard deviation which is determined from a limited monitoring program of the existing outfall. Although the errors involved in the calculations are quite large, the technique yields an order of magnitude prediction. The method finds that the existing Royal Roads outfall meets the environmental standard of a shoreline median coliform count not greater than 1000 MPN per 100 ml. The method also predicts that the proposed Portsmouth outfall will be well within the environmental standard.