Water Resources Research Act Program

Details for Project ID 2017DC187B

In-Situ Comparison of Extensive and Intensive Greenroof Infiltration

Institute: District of Columbia
Year Established: 2017 Start Date: 2017-03-01 End Date: 2018-02-28
Total Federal Funds: $10,000 Total Non-Federal Funds: $4,800

Principal Investigators: Kamran Zendehdel, Thomas Harris

Abstract: Greenroofs are effective technique in dense cities such as the District of Columbia (DC), where so much surface area is taken up by roofs. Greenroofs provides an opportunity to mitigate stormwater runoff at its source. Two main greenroof categories are defined based on substrate depth: intensive (deep) and extensive (shallow). Compared to extensive greenroofs, intensive greenroofs are heavier and require a higher initial investment and more maintenance over the long term than extensive greenroofs. In addition, intensive greenroofs generally require more structural support to accommodate the weight of the additional growing medium and public use. Despite the large difference in soil volumes for intensive system and extensive system they are generally treated the same for stormwater credits. There has not been a side by side research comparison of the two systems to compare runoff. The nature of this research is to investigate the impact of growing media depth (intensive vs. extensive) in stormwater retention and detention while taking into various stormwater events. The findings of this research will enable policy makers how to assign credit to extensive and intensive greenroof based on their stormwater control benefits. In the DC area intensive greenroofs are provided the same stormwater credits as extensive greenroofs. In this study, we will use the UDC greenroof and its three existing media depth to study stormwater retention, detention and associated water quality. This is important to understanding what role intensive greenroofs actually plays in a resilient urban stormwater system. Currently, the stormwater credits are based on the 95th percentile storm approximately 1.7”. Greenroofs have large variables and need to be better tested to understand its effects. This research will compare 1 year of storms to see how deep storms infiltrate into the greenroofs substrates. Does an extensive roof manage just as much stormwater as an intensive roof? How does soil saturation impact this? And does intensive roofs potentially play a role in reducing flooding?