Watch an animation from ASLA’s Designing Our Future: Sustainable Landscapes online exhibition that explains how green infrastructure systems effectively manage stormwater. See how green roofs, bioretention systems, and permeable pavements actually work:
According to a report from the Sustainable Business Network of Greater Philadelphia, one inch of rainwater hitting one acre of asphalt over an hour yields 27,000 gallons of water. In many communities, this water flows into combined stormwater / sewer systems, which channel both sewage and rainwater together through underground pipes to central treatment facilities. Storms can quickly overrun these combined systems, leading to flooding with pollutant-laden water and even backed up sewage. In fact, in many older cities like Philadelphia, basements can flood with excrement during major storms, creating major public health issues in the process.
The term “Green infrastructure” is used to describe how networks of natural ecosystems also function as crucial community infrastructure, providing ecosystem services and improving environmental sustainability. In the context of managing stormwater, green infrastructure can be defined as man-made systems that mimic natural approaches. Green roofs, bioswales, bioretention ponds, and permeable pavements are a few key examples of local green infrastructure, and all work by turning hard asphalt surfaces into green, absorbent ones. For example, Green roofs can retain 40-60 percent of stormwater hitting rooftops. Bioswales and retention ponds can absorb water and channel or hold excess run-off, cleansing pollutants in the process. However, even just adding extra trees, which consume lots of water, can help. Evergreens and conifers were found to intercept 35 percent of water hitting them.
Adding in green infrastructure systems is not only good for managing water, but also good for communities. Green infrastructure can lower air temperatures, which is crucial in cities facing the Urban Heat Island effect. Green roofs can double-up as roof-top parks, farms, and natural habitats for wildlife, providing a range of benefits. Chicago alone has seven million square feet of green roofs, which are often filled with native plants. For communities facing tight budgets, green infrastructure systems are also the most cost-effective way to manage stormwater when compared with rebuilding crumbling underground pipes. Philadelphia, which charges homeowners and local companies for their runoff, is now considering $1.6 billion plan to use natural systems to alleviate its major stormwater management problems.
Sources: Grey to Green: Jumpstarting Private Investment in Green Stormwater Infrastructure, U.S. Environmental Protection Agency, and The Vancouver Sun.