Philadelphia’s Green Stormwater Infrastructure Landscape Guidebook

by Caitlin Glagola, Associate ASLA; Tim Linehan, Associate ASLA; and Rachel Streit

PWD’s GSI Landscape Design Guidebook / image: Philadelphia Water Department

The Philadelphia Water Department (PWD) has one of the most progressive stormwater management plans in the country to address the city’s combined sewer infrastructure. PWD’s Green City, Clean Waters program, which begins its 7th year this July, has constructed more than 600 stormwater management practices (SMPs) in the city, including rain gardens, tree trenches, stormwater planters, and stormwater bumpouts. These stormwater landscapes, collectively known as green stormwater infrastructure (GSI), slow, filter, and infiltrate rainfall to help prevent polluted runoff from entering the city’s sewers and waterways. GSI is versatile and fits into the urban fabric of Philadelphia to not only manage stormwater but also to mitigate urban heat, improve air quality, provide habitat, improve human health, increase land value, and improve quality of life for city residents.

Projects installed have been closely monitored to assess system functionality, plant health, resiliency, and overall aesthetic qualities. In the various SMPs, PWD has observed that species vary in their tolerances to moisture levels, concentration of pollutants, as well as sediment and trash. Each design considers these factors by establishing upper zones, lower zones, and entrance zones within a SMP. The boundaries for these hydrologic zones will depend on the designed maximum ponding depth, steepness of the side-slopes, frequency of inundation, and infiltration rate. / image: Philadelphia Water Department

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