Yale Environment 360:
“Benjamin Franklin, Philadelphia’s favorite son, described his city’s stormwater problem well: By “covering a ground plot with buildings and pavements, which carry off most of the rain and prevent its soaking into the Earth and renewing and purifying the Springs … the water of wells must gradually grow worse, and in time be unfit for use as I find has happened in all old cities.”
When he wrote this in 1789, many of Philadelphia’s water sources, the scores of streams that ran into the Schuylkill and Delaware rivers, were already cesspools of household and industrial waste. As they became intolerable eyesores and miasmic health hazards, the city simply covered them with brick arches, turned the streams into sewers, and on top constructed new streets, an expanding impervious landscape that left the rains with even fewer places for “soaking into the Earth.” ...
The city is now in the seventh year of a 25-year project designed to fulfill an agreement with the U.S. Environmental Protection Agency (EPA) to reduce by 85 percent Philadelphia’s combined sewer overflows. These overflows occur when heavy rains overwhelm the capacity of the city’s sewage treatment plants to handle the flow from both storm and sanitary sewers, forcing the diversion of untreated effluent into the system’s river outfalls. But rather than spending an estimated $9.6 billion on a “gray” infrastructure program of ever-larger tunnels, the city is investing an estimated $2.4 billion in public funds — to be augmented by large expenditures from the private sector — to create a citywide mosaic of green stormwater infrastructure.
Integrated into the city’s green spaces, streetscapes, and public and private buildings, this green infrastructure ranges from simple home rain barrels and downspout planters to complex bioretention swales underlain by drains, filled with sandy soil, and planted with resilient species of grasses, perennials, shrubs, and trees. Along with rain gardens, tree trenches, green roofs, and urban wetlands, this infrastructure will, as one study put it, “optimize and engineer the landscape” to mimic and restore its natural hydrologic regime. In the end, Philadelphia hopes by the mid-2030s to create the largest green stormwater infrastructure in the United States.”
