Types of Green Infrastructure
In New York City, Green Infrastructure describes an array of practices that use or mimic natural systems to manage urban stormwater runoff. Green Infrastructure controls stormwater by using it as a resource rather than a waste. Water is either directed to engineered systems for infiltration or detained at a slower rate before it enters the combined sewer system.
The right–of-way (or ROW) is the public area between the two property lines along the street that includes the sidewalks and paved roadway.
The word bioswale is generally used to describe planted areas that collect rainwater. DEP uses the term ROW Bioswale to describe planted areas in the sidewalk that are designed to collect and manage stormwater.
How does a ROW Bioswale Work?
What you see here is rainwater (“stormwater runoff”) flowing down the street gutter along the curb and into the ROW Bioswale. The collected stormwater is absorbed by the sandy soil on the top (engineered soil) and stone layer at the bottom, and seeps into the ground underneath in a process called “infiltration.” Water that is absorbed by the trees and plants or remains on the surface of the Bioswale is then released into the air as water vapor. This process is called “evapotranspiration.” Most of the curb runoff is being directed into the inlet, but during some rainstorms, water may go past the inlet and go straight to the catch basin. If the ROW Bioswale reaches capacity, the water will overflow at the outlet and go into the catch basin the way it normally would.
Stormwater Greenstreets, like ROW Bioswales, are planted areas designed to collect and manage stormwater that runs off the streets and sidewalks. However Stormwater Greenstreets are typically constructed in the roadway, are usually larger than ROW Bioswales, and have varying lengths, widths and soil depths based on the characteristics of the existing roadway.
Green roofs are made up of a top vegetative layer that grows in an engineered soil, which sits on top of a drainage layer. A green roof can be intensive, with thicker soils that support a wide variety of plants, or extensive, covered in only a light layer of soil and minimal vegetation.
Blue roofs are designed without vegetation for the primary purpose of detaining stormwater. Weirs at the roof drain inlets create temporary ponding and gradual release of stormwater.
Rain gardens are vegetated or landscaped depressions designed with an engineered soil layer that promotes infiltration of stormwater runoff into the underlying soil. In addition to direct rainfall, stormwater runoff from surrounding impervious surfaces, such as sidewalks and rooftops, can be directed in to the rain garden so it can be absorbed into the ground.
Permeable paving is a range of materials and techniques, such as permeable pavers or porous concrete, which allow water to seep in between the paving materials and be absorbed into the ground. Permeable paving can be used instead of traditional impermeable concrete or asphalt.
Subsurface Detention Systems
Subsurface Detention Systems with infiltration capability provide temporary storage of stormwater runoff underground. These systems have an open-bottom and can incorporate perforated pipe and stormwater chambers for added detention volume. Systems are primarily designed with a gravel bed that stores water until it can infiltrate into the ground.
Cisterns and Rain Barrels
Cisterns and rain barrels are watertight receptacles designed to catch and store stormwater off of roofs and other impervious surfaces. Cisterns are often larger than rain barrels and can be located underground, at ground level, or on an elevated stand. Rain barrels are connected to the existing downspout of a roof and reuse the stormwater for watering plants and other landscaping uses.