Cities are defined by water. Waterways define city edges and boundaries, shape growth and development, and provide essential resources for human populations and the built environment. However, development patterns have too often removed water from urban places, channeling stormwater out of the human environment and therefore restricting natural functions and ecosystem services at great economic expense.

In the past, stormwater has been treated as waste, and stormwater management has meant dispensing of runoff as quickly as possible after a rainfall. This approach has required expensive “gray” water infrastructure: concrete and metal pipes, gutters, tanks, and treatment plants to convey, detain, and treat stormwater before discharging it into local water bodies. In many cities, intense storms overwhelm the gray infrastructure system, resulting in an outfall of polluted water into nearby streams and rivers, and potentially causing impassable streets and flooded homes and businesses. In cities across the country, gray infrastructure systems are under-maintained and reaching the end of their useful lives. Replacing this aging infrastructure can be a prohibitively expensive proposition.

Such a singular approach to stormwater management is no longer possible or desirable. In an age of climate change, urbanization, and increasingly frequent, intense storms and prolonged, devastating droughts, cities are now treating stormwater as a resource to be valued, not waste to be managed.

Green stormwater infrastructure reintroduces ecological functions back into the built environment. Soil-water-plant systems—including biofiltration planters, bioretention swales, trees, and permeable pavements—intercept stormwater before it reaches gray infrastructure. Some water is infiltrated into the ground, some is evaporated into the air, and some is temporarily stored before being slowly released into the sewer system. Green stormwater infrastructure helps to reduce runoff volume to gray infrastructure and filter pollutants, protecting water quality and mitigating risks of flooding. Investments in green stormwater infrastructure complement gray infrastructure and may extend the useful life of major capital street and sewer projects. In addition to its hydrological role, green stormwater infrastructure can offer valuable co-benefits, like calming traffic and beautifying the urban landscape. An integrated approach to green stormwater management in the public right-of-way is central to the design of resilient urban landscapes.