Stormwater Temperature Mitigation Beneath Porous Pavements: Fid-Bau Portal

Stormwater Temperature Mitigation Beneath Porous Pavements

Barbis, James / Welker, Andrea L.

This study investigates the effect of infiltration beds beneath porous pavements on stormwater temperature. With the use of traditional parking lot stormwater management techniques, stormwater flows via sheet flow across an impervious surface to a collection point. As the stormwater travels across, there is a transfer of heat energy between the pavement and the rainwater. In the summer months, when the pavement's surface can become very hot, this heat transfer can result in high runoff temperatures. If this hot water enters an aquatic ecosystem it can have detrimental effects on the behavior, metabolism and health of the aquatic organisms. This study investigates the use of porous pavement infiltration practices as a form of temperature mitigation through conduction between the warm stormwater and the stone infiltration bed. A parking lot on the campus of Villanova University was the focus of this study. In 2007, the parking lot was retrofitted with a 30 m (100 ft) by 9 m (30 ft) section of porous pavement parking spaces. The porous pavement section was designed so that half of the pavement (15 m by 9 m) was pervious concrete, and the other half was porous asphalt. The 270 m² porous pavement area has a drainage area of 730 m², which is 100% traditional asphalt. Underneath the porous pavement surface is an infiltration bed consisting of a limestone aggregate capable of storing up to 0.6 m (2 ft) of stormwater. For this study the air, incoming stormwater runoff, and porous pavement surface temperatures were recorded in 10-minute intervals, while the temperature of the infiltrating water was recorded at the bottom of the infiltration bed in 5-minute intervals. The average, maximum, and minimum temperatures for all of the temperature locations were calculated. For the air and porous pavement surface temperatures these calculations were based on the data from the beginning of the storm event until the last rainfall was recorded. The stormwater runoff temperature data was analyzed from the beginning of the storm until 20 minutes after the storm had ended. This end point was selected to allow for all of the runoff to enter the bed, but to prevent post-storm heating from effecting the calculations. Finally, the infiltration bed average, maximum, and minimum was calculated using the data from the beginning of the storm until the bed completely emptied. Twelve storms were analyzed from March 2009 through August 2009, and the results show that the porous pavements and infiltration bed were effective in reducing the temperature of high temperature runoff. This reduction in average temperature and temperature range supports the hypothesis that the thermally enhanced stormwater transfers its heat energy to the stone bed.