Mosinee, WI Environmental Rules: Flood Elevation Requirements (2026)

Article V of Chapter 42, the city's floodplain zoning article, defines flood protection elevation as a point two feet of freeboard above the water surface profile of the regional flood, a safety margin meant to cover unknowns like ice jams, debris and wave action that computed flood heights do not capture. That definition becomes an enforceable standard in the flood fringe district under Section 42-1259: any habitable structure built, altered or moved into the flood fringe must have its lowest floor, excluding basement or crawlway, at or above the flood protection elevation on fill, and that fill must be at least one foot above the regional flood elevation and extend a minimum of 15 feet beyond the structure.

A basement or crawlway floor may sit at the regional flood elevation only if floodproofed to the flood protection elevation; no basement or crawlway floor is allowed below the regional flood elevation at all. The article's general development standards in Section 42-1162 require the zoning administrator to review every permit application for whether the building site is reasonably safe from flooding, and to require anchoring, flood-resistant materials and protected mechanical systems for construction in flood-prone areas. Where existing street or sewer elevations make the fill standard impractical, the department may authorize alternate floodproofing measures instead.

Subdivision-level filling carries its own related rule elsewhere in Chapter 42: lots in a new subdivision must be filled to at least one foot above the flood protection elevation for that area, referencing the flood profile attached to Article V. Mosinee's river frontage on the Wisconsin River is why this article exists at all; the floodplain district system (floodway, flood fringe overlay and general floodplain district) maps directly onto the city's shoreline exposure. Any owner planning new construction, additions or substantial improvement on land near the river should confirm with the zoning administrator whether the parcel falls inside the mapped floodway or flood fringe before applying for a permit.