In urban areas excess water is collected in an engineered system of stormwater drains to control flow. Along its path, stormwater runoff may collect debris, sediment, and contaminants, resulting in negative environmental impacts to the water bodies into which it ultimately flows. Additionally, many large U.S. cities have combined sewer and stormwater systems in which large rainfall events may produce high stormwater flows that result in untreated sewage flowing directly into natural water bodies, further contributing to water quality degradation.
Green infrastructure may be implemented in urban and rural areas as a means to manage runoff entering stormwater drainage systems. In contrast to traditional grey infrastructure, such as stormwater drains, green infrastructure mimics natural, pre-development landscapes and their ability to capture, retain, and reuse water on-site. Green systems reduce stormwater flows, help to restore natural hydrology patterns, and improve water quality.