Runoff Quality Analysis of Urban Catchments with Analytical Probabilistic Models

The assessment of stormwater runoff pollution from urban catchments is addressed within a probabilistic framework. The methodology utilizes probability density functions of rainfall event characteristics, a runoff coefficient based rainfall-runoff transformation, and commonly used pollutant buildup and washoff processes representations. Employing derived probability distribution theory, analytical probabilistic runoff quality models are derived using exponential buildup and washoff functions. The derived analytical models yield expressions for expected event pollutant washoff load, annual average washoff load, the probability distribution of event washoff load, and the long-term average pollutant event mean concentration (EMC). These derived models are verified with available field data from an urban catchment located in the Greater Toronto Area. The verification results suggest that these analytical probabilistic models can be used for the assessment of runoff pollutant loads from urban catchments during planning-level analyses. These are computationally efficient closed-form mathematical expressions that can be easily incorporated into the spreadsheets and are thus a useful tool as an alternative or complement to more resource-intensive simulation models.