Worldwide, cities are learning from nature how to better manage stormwater runoff. A number of features are being employed to slow water down, allow it to sink into soils, where it is cleaned through natural processes. These features vary by site but include green roofs, rain gardens, roadside plantings, rain barrels, bioswales, tree trenches, and porous hard surfaces.Concerns over stormwater management have been around for years and cities are learning from each other. A 2013 article in Yale Environment360, To Tackle Runoff, Cities Turn to Green Initiatives by Dave Levitan, provides some recent examples and resources.
In an intact ecosystem, vegetation provides a filtering mechanism through providing above ground structures that slow water and allow sediments to settle out. Vegetation and soils slow water down, allowing it to soak into the soil, where it is filtered and cleaned as it moves through the soil’s pores and is subject to the rich soil ecosystem of fungi, bacteria, plant roots, and other organisms. These services are distributed throughout the whole ecosystem so that no matter where rain falls, it is slowed and absorbed or stored aboveground in rivers and lakes to be used by the ecosystem’s inhabitats.
Due to so many impervious structures in cities, such as roads, parking lots, buildings, and sidewalks, stormwater doesn’t have a chance to soak into the ground as it would in a natural system of plants and soils. For example, in New York City, impervious surfaces cover 72 percent of the city’s surface. According to an article in Yale Environment 360, “Ten trillion gallons of rainwater per year flow over rooftops and roads around the U.S., picking up contaminants that include bacteria, oil and grease, metals, pesticides, and many others. When a rainstorm is big enough, the runoff causes overflows from outdated sewer systems that combine both raw sewage and stormwater in a single pipe. This tide of pollutants ends up in surrounding waterways that serve as drinking water sources and recreational areas.” The problem is worse with the first flush of rain. Architect Ate Atema is working on a project in Brooklyn and has found that “The first 0.15 inches of rain more or less takes 80 percent of the mass contaminant load off the street.”Edit Summary