Many urban areas, but particularly cities, have combined sewer systems which carry both stormwater and wastewater. During heavy rains, these systems can overflow into waterways; impairing the health of our waterways for fishing and swimming.
New York City is required by legislation to reduce these “combined sewer overflows.” The reduction has historically been achieved using traditional “grey” infrastructure such as storage tunnels and wastewater treatment plants.
By introducing green infrastructure instead, natural systems can absorb 90% of all rainfall or the first inch of rain, which reduces rainfall runoff at the source.
To meet the legislation requirements and sustainability objectives of the city, we are working with the New York City Economic Development Corporation and the New York City Department of Environmental Protection, with the intention of saturating the city streets with as many right-of-way (ROW) bioswales as possible.
The DEP uses the term ROW Bioswale to describe planted areas in the sidewalk that are designed to collect and manage stormwater. They consist of a swaled drainage course with gently sloped sides (less than 6%) and filled with vegetation or compost
The three geographically distinct areas for the plan are:
531 acres of the Newtown Creek sewershed in Brooklyn
325 acres across the Westchester Creek sewershed in the Bronx
537 acres in the Bowery Bay sewershed in Queens
Benefits of bioswales
Bioswales are relatively cost effective and help “green” a local area; they play a part in reducing the heat island effect and in absorbing carbon emissions. Other on-street green infrastructure options like narrower greenstrips and permeable pavement are also being considered. There are numerous factors to consider, with the most critical being good soil conditions, maintaining pedestrian and vehicular access, and avoiding existing utilities.
We are also analysing and designing various green infrastructure practices (such as rain gardens, permeable pavement, and subsurface detention) within multiple NYC public properties including seven city parks, three public housing campuses, and a public school.
The bioswales range in size, with the largest being 5ft wide and 20ft long, and generally feature trees, landscaping, gravel, and other associated sidewalk and drainage infrastructure. We are responsible for site analysis, hydrologic analysis, geotechnical engineering, civil engineering design, and construction administration.
Managing urban infrastructure complexity
How could we assess the thousands of location options in an area of this size? To appraise each potential location we needed to collect information on up to 78 fields of data. To simplify this complex process, we developed our own mobile tool called Marq. Using Marq increased efficiency, reduced human error, and allowed us to collect records of locations and link them via a mapping and data system called ArcGIS.
Data collected in the field was processed in a format that was useful and manageable for our client’s asset tracking database. We leveraged our expertise with BIM principles to seamlessly translate data collected from the field into the design drawings, which ensured consistency in data management.
We successfully designed, planned, and constructed 140 ROW bioswales across 24 miles of city streets within a 500-acre sewershed in Brooklyn, all within three years. We also designed 30 ROW bioswales across 13 miles of city streets for a 325-acre sewershed in the Bronx and over 250 ROW bioswales for a 537-acre sewershed in Queens.