Verification of a numerical beach water quality model

Abstract

A dynamic two-dimensional finite difference water quality model was developed to predict the fecal coliform densities at the Toronto, Ontario, Eastern Beaches resulting from storm-water discharges. There are 10 storm-water and 2 combined sewer overflows discharging to the beach. Site-specific data were collected for use in the model. This data included local bathymetry, currents, dispersion, fecal coliform mortality rates, winds, receiving water fecal coliform densities, and discharge pollutographs. Specially designed field fecal coliform surveys were required to calibrate and verify the model since the storm effects are very dynamic in both time and space. The verified model was then used to estimate the reduction in fecal coliform densities at the beaches for different intensity storms for different remedial works. The improvements resulting from the different remedial works were quantified as the number of hours when the fecal coliform densities exceeded 100 counts/dL. Key words: beach fecal coliform predictions, storm runoff, water quality, numerical modelling, verification.