Sewershed NR-023 · NYC DEP Combined Sewer Overflow Tributary Area
NR-023 - Flatiron, Manhattan
Properties in this area share the NR-023 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 Flatiron, Manhattan specifically.
NR-023 is a combined sewer area covering 883 properties in Flatiron, Manhattan. Flood Form rates 62% of them Moderate or High for stormwater exposure, and 29% for groundwater. 30% of lots have yard area that legally qualifies for on-site infiltration. Ground elevation is typically 34 ft. The median building dates to 1910. 32% of parcels sit over a historic stream or pond. According to NYC DEP green infrastructure records, this sewershed drains to East River / Open Waters. NYC DEP has built 4 green infrastructure assets here.
883
Properties in sewershed
29.9%
Legally eligible for on-site infiltration
62%
Stormwater exposure: Moderate or High
29%
Groundwater exposure: Moderate or High
What sets NR-023 apart
34 ft
Median ground elevation
98%
Average impervious cover per lot
1910
Median year built
32%
Properties over a historic stream or pond
Stats computed from Flood Form’s NYC parcel data as of October 9, 2026
Common solutions for Flatiron 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
- NR-049Chelsea260 properties · 36% with Moderate or High stormwater exposure
- NCM-087Flatiron123 properties · 20% with Moderate or High stormwater exposure
- NR-027Chelsea867 properties · 58% with Moderate or High stormwater exposure
- NR-024Chelsea420 properties · 75% with Moderate or High stormwater exposure
- NR-020West Village385 properties · 59% with Moderate or High stormwater exposure
- NCM-045Midtown South483 properties · 50% with Moderate or High stormwater exposure
Want to see where your specific property stands?
Get Your Property’s Flood Form