Urban areas contain substantial expanses of hardscape in the form of buildings, paved roads, parking lots and concrete sidewalks. The impervious nature of these surfaces leads to runoff during periods of heavy precipitation.
Up to 55 percent of precipitation in urban areas may be in the form of stormwater runoff. In addition, compacted soils with poor drainage will also contribute to runoff. Environmental drawbacks of stormwater runoff include erosion of slopes and other surfaces, overloading municipal wastewater treatment systems and introduction of pollutants (chemicals, oils, fertilizers) into natural bodies of water. Common pollutants and their sources include copper from brake pads, roofing materials and pesticides; lead and zinc from roofing materials; and phosphorus and nitrogen from fertilizers (see ref 1 below).
High levels of fertilizers in the water, especially phosphorus, may lead to Eutrophication, which is the buildup of nutrients in natural bodies of water. The consequences of Eutrophication include algal blooms which are fed upon by microorganisms. When those microorganisms die, the oxygen in the water is depleted thus adversely affecting fish and other aquatic wildlife.
Stormwater management occurs more efficiently in natural settings such as forests, open fields and wetlands. The soil is more permeable and allows for effective water infiltration thus reducing runoff.
To simulate this in urban settings, green infrastructure is increasingly becoming a popular alternative to traditional ‘gray’ infrastructure. By definition, green infrastructure refers to “constructed features that use living, natural systems to provide environmental services, such as capturing, cleaning and infiltrating stormwater; creating wildlife habitat; shading and cooling streets and buildings; and calming traffic” (see ref. 2). Benefits of GI include temperature modification in urban areas, enhancing street and sidewalk aesthetics and reducing and filtering stormwater runoff. There are several types of green infrastructure that may be utilized in urban settings. Those include urban forests, green roofs, rain gardens and bioswales (see ref. 1).