Sewershed OH-021 · NYC DEP Combined Sewer Overflow Tributary Area
OH-021 - Gravesend, Brooklyn
Properties in this area share the OH-021 combined sewer — during moderate-to-heavy rain, runoff can exceed pipe capacity faster than it drains, which is what drives sewer backup exposure block by block. Here’s what that looks like for Gravesend, Brooklyn specifically.
OH-021 is a combined sewer area covering 6,804 properties in Gravesend, Brooklyn. Flood Form rates 44% of them Moderate or High for stormwater exposure, and 6% for groundwater. 72% of lots have yard area that legally qualifies for on-site infiltration. Ground elevation is typically 24 ft. The median building dates to 1928. 5% of parcels sit over a historic stream or pond. According to NYC DEP green infrastructure records, this sewershed drains to Coney Island Creek. NYC DEP has built 29 green infrastructure assets here.
6,804
Properties in sewershed
71.6%
Legally eligible for on-site infiltration
44%
Stormwater exposure: Moderate or High
6%
Groundwater exposure: Moderate or High
What sets OH-021 apart
24 ft
Median ground elevation
90%
Average impervious cover per lot
1928
Median year built
5%
Properties over a historic stream or pond
Stats computed from Flood Form’s NYC parcel data as of October 9, 2026
Common solutions for Gravesend properties
Downspout Diversion
Redirects roof runoff away from the combined sewer and into landscaped or permeable areas on the lot.
Infiltration System
Drywells or infiltration chambers that let stormwater soak into the ground on-site instead of entering the sewer.
Detention System
Holds stormwater temporarily and releases it slowly, reducing peak flow into the combined sewer during a storm.
Drain Improvement
Upgrades yard, area, or foundation drains so water is carried away from the building instead of pooling.
Foundation Waterproofing
Protects the foundation from groundwater intrusion, relevant where groundwater exposure runs high.
Nearby sewersheds
- OH-015Bensonhurst21,675 properties · 37% with Moderate or High stormwater exposure
- OH-017Bay Ridge8,555 properties · 35% with Moderate or High stormwater exposure
- OH-002Borough Park17,937 properties · 34% with Moderate or High stormwater exposure
- CI-004Flatlands32,638 properties · 46% with Moderate or High stormwater exposure
- CI-006Flatlands2,349 properties · 43% with Moderate or High stormwater exposure
- OH-018Bay Ridge4,732 properties · 35% with Moderate or High stormwater exposure
Want to see where your specific property stands?
Get Your Property’s Flood Form