Sewershed CI-004 · NYC DEP Combined Sewer Overflow Tributary Area
CI-004 - Flatlands, Brooklyn
Properties in this area share the CI-004 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 Flatlands, Brooklyn specifically.
CI-004 is a combined sewer area covering 32,638 properties in Flatlands, Brooklyn. Flood Form rates 46% of them Moderate or High for stormwater exposure, and 9% for groundwater. 79% of lots have yard area that legally qualifies for on-site infiltration. Ground elevation is typically 28 ft. The median building dates to 1925. 3% of parcels sit over a historic stream or pond. According to NYC DEP green infrastructure records, this sewershed drains to Jamaica Bay and Tributaries. NYC DEP has built 8 green infrastructure assets here.
32,638
Properties in sewershed
79.2%
Legally eligible for on-site infiltration
46%
Stormwater exposure: Moderate or High
9%
Groundwater exposure: Moderate or High
What sets CI-004 apart
28 ft
Median ground elevation
82%
Average impervious cover per lot
1925
Median year built
3%
Properties over a historic stream or pond
Stats computed from Flood Form’s NYC parcel data as of October 9, 2026
Common solutions for Flatlands 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
- CI-005East Flatbush13,975 properties · 51% with Moderate or High stormwater exposure
- CI-006Flatlands2,349 properties · 43% with Moderate or High stormwater exposure
- OH-015Bensonhurst21,675 properties · 37% with Moderate or High stormwater exposure
- OH-021Gravesend6,804 properties · 44% with Moderate or High stormwater exposure
- 26W-003Brownsville12,515 properties · 41% with Moderate or High stormwater exposure
- OH-002Borough Park17,937 properties · 34% with Moderate or High stormwater exposure
Want to see where your specific property stands?
Get Your Property’s Flood Form