Green Roof Runoff Impact

Stormwater response of a green roof is indeed highly impacted by the climate conditions and by the green roof structure itself and this conditions make generalization a very difficult task.

Green roof runoff impact.

A green roof will typically intercept the first 5mm and more of rainfall providing interception storage. Due to the volume reduction actual nutrient loadings from green roofs are less than asphalt roofing runoff or otherwise manageable at the downspout. In germany between 40 100 of rainfall can be retained dependent. Green roofs are unique in that they have the ability to capture and retain a volume depth of rain from each rainstorm.

In this paper an empirical formulation is compared to a conceptual framework to investigate the stormwater runoff coefficients. Environmental and human health benefits of green roofs include air purification urban heat island amelioration lower building energy costs increased urban biodiversity reduced stormwater runoff and improved stream water quality. The amount will be dependent on the depth and type of substrate in the green roof system. Green roof runoff does contain concentrations of some nutrients and other parameters but values are in line with other planted systems.

In the summer a green roof can typically retain between 70 80 of the run off.