by U. S. Environmental Protection Agency (Author)
Cities employ a variety of measures to manage stormwater runoff. However, most do not take advantage of the stormwater utility benefits trees provide. Grey stormwater systems use curbs, gutters, drains, pipes, ponds, vaults, and outfalls to move water quickly to containment and/or treatment areas or to receiving waters. Alternatively, green stormwater systems manage stormwater on site with overflow ability, creating areas that mimic nature. Vegetation, swales, wetlands, buffer zones, and pervious surfaces capture, filter, and slow stormwater runoff. Volume is managed through evapotranspiration, infiltration, and soil moisture recharge. Trees are typically not considered part of either grey or green stormwater management systems; they are generally, and falsely, considered to be of landscaping value. Planting a tree just for landscaping is not taking advantage of the stormwater utility benefits and other environmental services it provides. In urban areas, trees are part of the managed municipal infrastructure. A street tree, which is generally a publicly managed tree found growing within the right-of-way, offers unique opportunities to increase the effectiveness of grey and green stormwater systems.