Staten Island Flood Map

Stormwater

In Flood Form's data, 32% of lots in Staten Island rate Moderate or High for stormwater.

Parts of Staten Island still lack a fully built sewer system. Bluebelts, the streams and wetlands kept as natural drainage, cover about a third of the borough.^[1][2]

In Ida the North Shore was among three community districts that together took a fifth of all damage citywide.^[3]

City sewers are built to drain roughly 1.75 inches of rain an hour, and some older ones less: before 1977 each borough set its own standard.^[1]

Hurricane Ida brought 3.15 inches in a single hour to Central Park in 2021. More than half of the damage it caused fell outside both FEMA floodplains and the City's own stormwater flood scenarios.^[1][3]

Flooding doesn't always follow the heaviest rain: in the September 2023 storm, parts of southern Queens and coastal Staten Island flooded badly with little intense rainfall, which the Comptroller tied to gaps in drainage.^[4]

Sewer backup

In Flood Form's data, 19% of lots in Staten Island rate Moderate or High for sewer backup, and 22% drain to a combined-sewer outfall.

About 60% of the city's sewer system is combined, carrying both sewage and stormwater in one pipe. When intense rain exceeds pipe capacity, that mix can back up through basement drains and fixtures.^[5]

DEP reports that rain-driven backups are now the most common kind, overtaking backups from grease and wipes, and that about 74,000 properties, most of them one- and two-family homes, are vulnerable in a storm of 1.75 inches per hour.^[5]

Homes whose drains and fixtures sit below the nearby sewer, such as basements reached by a downward-sloping driveway, are the most likely to back up.^[5]

Coastal flooding

In Flood Form's data, 12% of lots in Staten Island rate Moderate or High for coastal flooding. 7.6% fall in FEMA's 1% annual-chance floodplain, and 12% were inside the area Hurricane Sandy flooded in 2012.

Flood insurance claims and policies concentrate on the East Shore, in neighborhoods such as Oakwood Beach and Ocean Breeze that the City has designated coastal districts.^[2]

Coastal flooding comes mainly from storm surge, while tidal flooding can happen on ordinary high tides without a storm.^[2]

FEMA flood maps show coastal and river flooding, not the rainfall and sewer flooding behind most basement deaths in Ida.^[6]

Groundwater

In Flood Form's data, 7% of lots in Staten Island rate Moderate or High for groundwater, and 12% sit near a buried historic stream or pond.

The City's hazard mitigation plan names groundwater flooding a particular concern where neighborhoods were built while pumping held the water table down, and notes parts of Brooklyn and Queens where groundwater sits less than 10 feet below the surface. It adds that research on the problem is at an early stage.^[2]