Green Roof Stormwater Management

Green roofs will intercept between 15 and 90 of rooftop runoff.

Green roof stormwater management.

Many of the vegetated roof policies and programs focus on stormwater management benefits. Variation in absorption rates can be as great as 50 based on differences in temperature wind evapotranspiration rates and plant uptake. Current green roof policies tend to be prescriptive based mandating a minimum depth and or composition of green roof growing medium. The plants and growing medium of a green roof absorb water that would otherwise become runoff and research indicates that peak flow rates are reduced by 50 percent to 90 percent compared to conventional roofs.

This course is about the different ways in which green roofs can be utilized as a stormwater best management practice and can supplement existing sewer infrastructure avoiding a number of weather related costs associated with climate change. Their major drawback is the initial cost. Absorption of runoff into a green roof system will vary between 50 60 and is related to the type of growing medium and plant cover variability. When it rains runoff flows directly into stormwater systems and nearby waterways.

Excessive rainfall can result in strains on these systems which can lead to flooding. A typical extensive green roof of 3 5 inches depth will reduce the volume of runoff by about 55 in central pennsylvania and attenuate the peak runoff rates to the level of the pre development land use.