Influence of Environmental Factors in Hydrodynamic Modelling of Bacterial Distribution in Stormwater Ponds

Abstract

Due to the typically large sizes of many stormwater ponds, numerically modeling the bacteria fate and transport within these ponds is more practical than in situ monitoring. However, bacteria fate and transport models lack proper verification and rely on numerous assumptions without proper validation of these assumptions. In this paper, a sophisticated hydrodynamic model is developed for estimating bacteria levels in the Inverness stormwater pond, in Calgary, Alberta, Canada, and is verified in two ways. First, the bacteria concentrations predicted by the developed model for several locations within the pond were compared to data collected during two separate field campaigns at the pond. Good agreement was observed and while it was found that contamination increased over time between the two field campaigns, the most contaminated location was consistently in the west wing. Second, fluid flow velocity vectors in numerous locations were measured and compared with the modeled results. The impacts of model assumptions and inputs on the bacteria distribution in the pond were also assessed. The model was run for various particle-attachment rate and sizes, various rain hyetographs and various wind conditions. It was found that synthetic hyetographs can be used for design purposes to find the optimal location for withdrawal. The effect of wind direction was found to be event specific and location specific. In general, wind was found to play a crucial role in the bacteria distribution in the pond.

Keywords: stormwater ponds, water quality, hydrodynamic modeling, environmental hydraulics, computational fluid dynamics, hydrological model HEC-RAS, E. coli