W.E. Watt

THERMAL ENHANCEMENT OF STORMWATER RUNOFF BY PAVED SURFACES

Abstract A methodology for predicting the thermal enhancement of stormwater runoff from paved surfaces is documented for a test facility in Kingston, Ontario, Canada. Prediction of runoff temperature is based on TRMPAVE, a mathematical model that was developed using a thermal energy balance approach and the one-dimensional heat equation to predict the surface temperature and temperature gradient in asphalt during dry-weather and wet-weather periods. Runoff temperature is then estimated as a function of rainwater temperature and surface temperature of the asphalt. In order to supplement wet-weather data, a number of simulated rainfall events were generated over a test plot to help develop, calibrate and verify the wet-weather model. Computer simulations for both dry and wet-weather periods compared well with measurements of temperature from the test plot. In addition, the average temperature of runoff contributed by the entire parking lot area was cooler than the average temperature of runoff from the test plot, but both values were higher than runoff from the upstream catchment. In light of the results obtained, TRMPAVE can be used to predict thermal loading from impervious areas.

Application of the log-normal and normal distributions to stormwater quality parameters

Abstract Concentrations of water quality constituents in urban stormwater are often expressed in probabilistic terms—using statistics such as the mean and standard deviation and selected quantiles. In many studies, the log-normal distribution has been assumed to apply. In this 3-year study, the distributions of concentrations of 14 constituents in five sources of run-off were studied—parking-lot run-off discharging into an on-stream pond, baseflow and event flow in a small suburban creek feeding the same on-stream pond, and the pond outflow under both baseflow and event flow conditions. Two probability distributions, log-normal and normal, were fitted and the goodness-of-fit was assessed using probability plots and the Cramer-von Mises test. Of the two, the log-normal was the better distribution in most of the cases tested. It was more suitable for parking-lot run-off and creek baseflow, and somewhat less suitable for creek event flow and pond baseflow. With a few exceptions, the log-normal distribution did not apply for soluble constituents (total dissolved solids, chlorides, sulphate, COD) and/or event outflow from the pond. In these cases the normal distribution was preferred. The composition of outflow from the pond was controlled by intense mixing of the incoming event run-off with the water stored in the pond. The assumption of an inappropriate probability distribution can result in substantial errors when estimating the mean concentration for censored data. This in turn can affect calculation of pollutant loads and extrapolation to estimate quantiles.

Removal of Selected Urban Stormwater Constituents by an On-stream Pond

A methodologyis presented for assessing the pollution control performance of an on-stream stormwater pond, and the application of this methodology to a specific facility in Kingston, Ontario, Canada is documented. This assessment is based on constituent mass balances for both baseflow and event conditions. Results on removal rates are provided for selected dissolved constituents, nutrients, suspended solids, metals and organic contaminants. In summary, dissolved constituents exhibit zero removal for baseflow periods and positive removal for events; nutrients and suspended solids exhibit negative removal for baseflow periods and positive removal for events; and metals and organics exhibit positive removal for both baseflow periods and events. Constituent removal appears to be controlled mainly by physical processes (sedimentation), and the uncertainties associated with the estimates of constituent loads are quantified.