City progresses toward climate resilience a year after Hurricane Ida.

New York City Mayor Eric Adams and the New York City Department of Environmental Protection (NYC DEP) observed the one-year anniversary of Hurricane Ida by announcing updates and progress on a portfolio of stormwater management initiatives as the city is anticipated to experience more extreme rainfall in the future.

Hurricane Ida brought the “heaviest rainfall in the city’s recorded history,” flooding streets, subways, homes and claiming 13 lives, soberly noted the mayor.

The following highlights more innovative approaches the city is taking:

Cloudburst Management

NYC and the city of Copenhagen are sharing best practices for stormwater management. Pilot projects aim to help manage cloudbursts, or extremely intense cells of rainfall that can impact portions of the city during a storm. The heavy downpours can drop large amounts of rainwater over a short time period and overwhelm the city’s sewer system capacity.

Cloudburst management implements a combination of methods that absorb, store and transfer stormwater to minimize flooding risk. Strategies seek to use open spaces to temporarily store stormwater until the rain event passes and the drainage system has capacity.

The city’s first cloudburst pilot project, at NYC Housing Authority’s (NYCHA) South Jamaica Houses, is designed to channel stormwater to three areas on site: two open grassy areas, and a basketball court that will be rebuilt at a lower elevation where runoff will flow.

Sankt Jorgen Park, Copenhagen cloudburst management masterplan image | credit Ramboll Studio Dreiseitl

When completed, the new South Jamaica Houses green infrastructure assets will be able to capture and hold approx. 300,000 gallons of stormwater.

Bluebelt Program Expansion

The city remains committed to expanding its Bluebelt ProgramBluebelts are a stormwater best management practice (BMP) in which natural streams, ponds and wetlands supplement constructed drainage systems to channel and filter runoff before it flows into the New York Harbor.

Presently, 94 bluebelts citywide — 83 in Staten Island, 10 in Queens and one in the Bronx – help to naturally drain large amounts of stormwater. Several additional bluebelts are currently in design, and DEP engineers are looking across the city to identify feasibility of future sites.

Daylighting Buried Streams

NYC has begun to daylight, or bring parts of previously buried streams back to the surface, historical watercourses that channel stormwater to the Harlem River and away from the sewer system heading to the Wards Island Wastewater Resource Recovery Facility. The practice removes unnecessary water and thus, adds capacity to the sewer network.

Daylighting the Tibbetts Brook watershed is expected to mitigate flooding along Broadway in the Bronx, while reducing sewer overflows that carry unclean water into the Harlem River.

Porous Pavement

As part of an ongoing pilot program, more than three miles of porous pavement have been installed within roadways in Queens and the Bronx. Porous pavement manages more stormwater runoff than typical curbside rain gardens since it replaces more asphalt. Engineers are currently designing more than 56 additional miles of porous pavement for Brooklyn and the Bronx.

In contrast, impervious surfaces like asphalt, concrete and stone don’t allow water to pass through for seepage into the ground. When rain falls on these surfaces, stormwater runs off into sewers or bluebelts – quickly diminishing capacity in drainage systems.

Onsite Retention Mandate

In February this year, NYC DEP finalized the Unified Stormwater Rule, which requires any newly developed or redeveloped property to include infrastructure, such as a green or blue roof, rain gardens, or storage, that will retain additional stormwater on-site.

On-site water storage deters or slows the flow of stormwater entering into the city’s sewer system and thus, mitigates flooding and reduces sewer overflows into waterbodies surrounding the city.