How green infrastructure will limit raw sewage in the Gowanus Canal

What might look like a really nice spot for an outdoor lunch is actually part of a larger effort by the city to understand just how much rain can be absorbed using green technology.

The newly restored Gil Hodges Community Garden in Park Slope has a lot of meters and gauges hidden under the sidewalk alongside it, helping the city to calculate how much rain a green system can catch and hold.

At the intersection of Carroll Street and Denton Place, the garden has become a part of city’s new green and grey stormwater management system. The work was completed by the New York Restoration Project with support from Joe Malone London and the NYC-DEP. 

The NYC-DEP estimates that the ‘bioswale‘ installed during the garden’s restoration will manage 150,000 gallons of stormwater each year by infiltrating it into the soil, which keeps it out of the cities overtaxed combined sewage system, reducing the overflows of raw sewage into the Gowanus Canal. The new park will help do that by using a rain garden, with very absorbent plants, porous pavers, so that water that falls where people walk can still get in the ground and, most importantly, a new bioswale beneath the sidewalk that collects water from the sidewalk and Denton Place.

City College of New York’s Sustainability in the Urban Environment program is the academic partner to the project, and it has installed various technology into the site to help assess the effectiveness of the bioswale in a three year study.

George Smith, the coordinator of CCNY’s program, explained to Technically Brooklyn the technology deployed at the site:

•  A bioswale is a water course designed to allow water to infiltrate into soil while also guiding it away from a site.
• The bioswale has been outfitted with 18 piezometers, along its course and at different depths, which measure water pressure, to help track stormwater infiltration over time.
• There are also rainbuckets installed above the garden to track total rainfall over the course of storm events, to help assess how much water gets infiltrated into the soil.
• Data will be reported on over a three year period, using graphs showing the volume of water (hydrographs), rainfall over time (hyetographs), infiltration rates, total precipitation and water quality.
• Meters in the garden transmit data wirelessly to scientists off site, as well as storing the data for local collection.
• Soil samples will also be taken on site to assess the system and water quality meters will be installed soon.

If you aren’t familiar with the concept of Combined Sewage Overflows, you may have been better off not knowing: older cities like New York often manage sewage from homes and businesses in the same pipes as the stormwater collected by streets and storm drains. That means these sewage systems are already so overtaxed that there is sometimes too much sewage alone in the system for the pipes. When that happens, they overflow untreated into the nearest river or canal. So, any rain is usually too much rain.

To take pressure off these water systems, cities are now trying to get more rain into the ground, using various strategies broadly known as “green infrastructure.”  NYC-DEP has released guidelines for monitoring pilot green infrastructure programs, like those at the garden.

CCNY’s Sustainability Program’s project at Gil Hodges Community Garden is being conducted in collaboration with Dr. Franco Montalto of Drexel University’s Sustainable Water Resource Engineering Lab and Dr. Joshua Cheng of Brooklyn College’s Environmental Science Analytical Center.