Stormwater Retention of an In-Series System Composed of a Green Roof, Constructed Wetland, and Bioretention Cell for a Single-Family Home

The need to develop a sustainable approach to stormwater management is rapidly becoming a priority as urban development and climate change alters urban hydrologic cycles. Green infrastructure (GI) is widely viewed as a sustainable method to managing stormwater. However, rarely have in-series systems of GI been monitored, even though most stormwater regulations require these practices to be installed. Additionally, studies on the effectiveness of GI in residential settings is lacking. This paper examines how an extensive green roof, constructed wetland (CW), and bioretention cell integrated in-series on a home in Rockville, Maryland, affected site hydrology during 116 storm events that occurred from July 2014 to June 2016. The effects of season, antecedent substrate water content, storm characteristics (size, intensity, and frequency), and green roof vegetation development (leaf area index and percent cover) on retention were evaluated. Collectively, the green roof, CW and bioretention cell stored 6,930.7 mm of stormwater over the 2-year study period. Given a total input of 19,019.1 mm over all storm events, the three systems collectively reduced site runoff by approximately 36.4%. Event size was the single biggest predictor of retention for all systems. When evaluating each system independently, the CW retained the most runoff (37.6% or 337.3 mm/m2 of water). Findings provide insight on the benefits of implementing GI in-series on residential properties.