From 2008 to 2011 Herrera assessed the hydrologic and water quality performance of a vegetated roof versus a metals roof and a pervious asphalt versus conventional asphalt basketball court in Redmond Washington’s Grass Lawn Park. The results from this monitoring indicated that the vegetated roof was effective at reducing peak flow rates and flow volumes; however, the vegetated roof was also a source of nutrients and copper relative to the adjacent metal roof. The results of the hydrologic monitoring of the basketball courts were confounded by the fact that the underdrain system beneath the pervious pavement basketball court was conveying shallow groundwater in addition to stormwater runoff. This resulted in an increased export of stormwater volume during the wet season relative to the conventional basketball court. Despite the groundwater exfiltration issue, the pervious pavement court reduced peak discharge rates by approximately 68.2 percent in the 2009, 2010, and 2011 wet seasons, and 93.4 percent in the 2009, 2010, and 2011 dry seasons.
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Final Data Report: Grass Lawn Park LID Monitoring (October 2008 to September 2011)
Reference: Herrera. 2011. Final Data Report: Grass Lawn Park LID Monitoring (October 2008 to September 2011). Prepared for The City of Redmond, by Herrera Environmental Consultants, Inc., Seattle, Washington.