Citation:

OConnor, T. Green Roof Research through EPA's Regional Applied Research Effort - slides. Presented at 2013 International Low Impact Development Symposium, St. Paul, MN, August 18 - 21, 2013.

Impact/Purpose:

Data will be presented that show green roofs are an effective low impact development tool. Two of the projects have resulted in reports that are available on the EPA website: National Service Center for Environmental Publications (NSCEP) (http://www.epa.gov/ncepi/). A final report for the third project is in the works.

Description:

The U.S. Environmental Protection Agency’s (EPA) Regional Applied Research Effort (RARE) allows the Regions of the EPA to choose research projects to be performed in partnership with EPA’s Office of Research and Development (ORD). Over the last decade, several green roof projects were initiated and performed in different EPA Regions, including Regions 2, 3 and 8. These projects provide results for different climatic conditions and a variety of green roof systems and sizes. The project in Region 3 was performed by the Pennsylvania State University (Berhage et al., 2009). Primarily this project was performed through the monitoring of replicate experimental setups using small-scale buildings exposed to the elements. Data were collected for 72 precipitation events from three green roofs and two flat asphalt roofs. A range of events were monitored including a high-intensity short-duration [1 in. (25 mm) in 30 min] event; and, a high-total precipitation steady-rate [2.65 in. (67.3 mm) over 8 hr] event. Data were also collected from winter snow events. Green roof performance was quite consistent during the warm summer months (limited runoff) but was more variable during winter months. Typically, runoff rates from green roofs were non-existent until the systems were saturated at which point runoff flow roughly equaled the rate of precipitation input. Even when rainfall led to saturated conditions, green roofs significantly increased the time to peak runoff as compared to the flat control roofs. Annual reductions in runoff were about 50% with nearly 100% in summer and approximately 20% over the non-growing season. Water quality parameters were evaluated in real time (e.g., flow, turbidity, electrical conductivity [EC], pH and nitrate) and by grab samples (e.g., color, nutrients and ions). Green roof runoff was colored yellow, had higher pH and EC, and generally had equal or higher concentrations of the nutrients and ions measured in solution. Loadings (in lb/acre) of various nutrients, with the exception of nitrate, and hardness from green roofs were greater than from flat asphalt roofs. However, other ion loadings in the green roof runoff were not statistically different from flat asphalt roofs. In summer, when green roofs retained nearly all precipitation, there was limited nitrate loading from the green roofs. The water quality impacts of the green roof are thus seasonal, and depend on loadings from the planted system, background precipitation concentrations, and runoff rates.

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