Hillsborough County, NH Environmental Rules: Flood Zones (2026)

Floodplain management in New Hampshire is handled at the municipal level under RSA 674 (zoning) and at the state level for wetlands under RSA 482-A. Hillsborough County itself has no floodplain authority. FEMA published the Digital Flood Insurance Rate Map (DFIRM) for Hillsborough County (community panel set 33011C), originally effective in 2009; FEMA has since conducted Discovery and preliminary remapping for the Merrimack and Nashua River watersheds. NFIP-participating communities in Hillsborough County include Manchester, Nashua, Merrimack, Hudson, Litchfield, Lyndeborough, Milford, Mont Vernon, Bedford, and most other municipalities, each of which has adopted a local floodplain ordinance meeting the minimum standards in 44 CFR Part 60. Development in a Special Flood Hazard Area (SFHA) - Zones A, AE, AO, AH, and floodways along the Merrimack River, Nashua River, Souhegan River, and tributaries - generally requires a local floodplain permit before any building permit can be issued. Federal NFIP rules require new residential structures in the SFHA to have the lowest floor elevated to or above the Base Flood Elevation (BFE); many New Hampshire towns require freeboard of 1-2 feet. Substantial improvement and substantial damage thresholds (50 percent of pre-improvement market value) trigger full compliance with the floodplain ordinance. Separately, RSA 482-A (the Fill and Dredge in Wetlands law) requires a permit from the New Hampshire Department of Environmental Services (NHDES) for any excavation, removal, fill, or dredge in wetlands or surface waters. Municipalities may also designate prime wetlands meeting RSA 482-A criteria (minimum 2 acres, at least 4 primary functions, at least 50 feet wide). The Floodplain Management Program at NH Office of Planning and Development provides technical assistance to communities.