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Greening the streets of Philadelphia

Like many older US cities, more than half of Philadelphia is served by combined sewers that carry both sewage and stormwater. Heavy rain or snow can cause overflows that discharge into local rivers through the city’s outfalls.

Project ‘Green City, Clean Waters’ stormwater management plan, Philadelphia, USA

Client City of Philadelphia Water Department

Expertise Conceptual planning, field location surveys and mapping, geotechnical engineering, green stormwater design

The Philadelphia Water Department decided to invest in green infrastructure to collect and treat stormwater runoff at the source, through a variety of sustainable urban drainage systems that reduce the amount of stormwater entering the combined sewer system. Primarily developed to reduce volume and pollution in rivers, the ambitious 25-year programme is likely to produce social, economic and environmental benefits too, supporting urban regeneration and creating a green legacy for future generations.

Our experts prepared final design plans and specifications for several projects including stormwater curb extensions, infiltration trenches that water trees with stored stormwater, and planters that collect drainage from the street. We modelled these and other stormwater management practices, resolved construction process issues that occur when working in a dense urban environment, and helped to optimise the designs to improve durability and maintenance.

Greening Philadelphia’s neighbourhoods enhances their appearance and improves air quality. Trees, green roofs and rain gardens create a cooling effect that helps to reduce heat stress-related fatalities during heatwaves.


tonnes CO2 emissions avoided or absorbed

The Green City, Clean Waters stormwater management plan is closely integrated with local and national policies, forming part of efforts aimed at improving the city’s resilience to climate change and deliver social, economic and environmental benefits.

Green stormwater infrastructure improves ecosystems by providing a natural water quality filter and limiting erosion of waterways caused by high flows, both of which benefit aquatic species. The restoration of streams and wetlands creates habitats needed to support rich and diverse aquatic life.

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