Mamaroneck advances multi‑site flood mitigation designs; seeks county grants to halve local cost

Town Engineer Robert Wasp and consultants updated the Town Board on June 16 about an ongoing flood mitigation program that grew out of a 2024 storm‑sewer and drainage evaluation identifying 13 flood‑prone basins. "Flooding is probably the most impactful environmental hazard that this town faces," Wasp said as he introduced the project timeline and funding strategy.

Consultants from HJM Architects & Engineers described three projects now at bid‑document stage — Subbasin 1 (Fenimore Road culvert replacement), Subbasin 3 (7 Country Road) and Subbasin 13 (Old White Plains Road) — that the town expects to finalize for public bidding by the fourth quarter of 2026 and to complete construction by fall 2027. Jim Moran, a vice president at HJM, said those three projects together total about $3,100,000 and are being sized to convey a 25‑year storm event.

Engineers cautioned that larger watershed constraints remain. Sean Peters, the lead designer, said Subbasins 2 and 7 encompass roughly 180 acres and are limited by an existing culvert under I‑95 that conveys about 200 cubic feet per second (cfs), roughly half the flow the drainage produces during a 10‑year storm. "There's that bottleneck that goes to the village of Larchmont," Peters said, noting that upsizing the highway culvert would be costly and would require regional coordination.

The engineering team said modeling shows the proposed improvements would substantially reduce both the number of structures experiencing flooding in many basins and the severity of flooding at nodes that remain exposed under extreme storms. For example, in one subbasin design the number of flooded structures in a 10‑year event would fall from 33 to 13, with much lower flood depths at those remaining nodes.

Funding is the primary constraint. Wasp told the board the town has applied to the Westchester County Flood Mitigation Grants Program, which offers 50% matching funds for construction. If the county approves the town’s application for the three construction‑ready projects, the county’s share would reduce the town’s cost for that group to roughly $1,500,000. The town is also pursuing green stormwater infrastructure grants for additional design work on Colbert Drive and Adrian Circle.

During an extended public Q&A, residents raised downstream impacts, private driveway culverts, and erosion control. Engineers said forthcoming HEC‑RAS channel analyses will evaluate driveway crossings, culvert sizes and channel elevations; where private driveway culverts must be replaced to achieve project benefits, the town will need to coordinate with homeowners. Wasp also said erosion‑control measures such as riprap and localized stabilization are part of planned designs.

The board directed staff to pursue available grants, to continue design sequencing that prioritizes sites with fewer downstream constraints, and to coordinate with neighboring municipalities (via LISWIC and other joint working groups) for projects that might affect or depend on upstream/downstream infrastructure. The board and staff emphasized that many projects aim to reduce flood severity rather than eliminate all flooding given physical and budget limits. The presentation and public Q&A ran between the staff introduction (SEG 267) and the end of public questions (SEG 1619).