Environmental Rules in Washington County, WI (2026)
4 rules for unincorporated Washington County, Wisconsin.
Verified from official government sources
Stormwater Management
Washington County requires a stormwater management plan for qualifying land development that holds post-development peak discharge rates to predevelopment levels for the one-, two-, ten- and 100-year storms, and cuts total suspended solids by 80% for new development or 40% for redevelopment of parking areas and roads.
Washington County Stormwater Management Standards
Some RestrictionsWashington County Code § 238-8A(1)(b), (c)[1], § 238-15C(1)(a)
To minimize stream bank erosion and the failure of downstream conveyance systems, the calculated post-development peak stormwater discharge rates shall not exceed the calculated predevelopment discharge rates for the one-, two-, ten-, and 100-year, twenty-four-hour design storms in accordance with the modeling requirements in § 238-11A of this chapter. ... For new land development and infill de...
Erosion Control
Washington County requires an erosion and runoff control permit before any land-disturbing construction activity that disturbs 4,000 square feet or more, and the approved erosion control plan must hold sediment discharge to no more than five tons per acre per year until the site is stabilized.
Washington County Construction Site Erosion Control
Some RestrictionsWashington County Code § 238-6A(1), § 238-7A(1)(b), § 238-15C(1)(a)
Disturbs 4,000 square feet or more of total land surface area; or ... For sites that disturb one acre or more of total land surface area, an erosion control plan shall by design achieve a runoff discharge of no more than five tons of sediment per acre per year from sheet and rill erosion during land-disturbing activities as compared with no sediment or erosion controls, until the site is stabil...
Flood Zones
In the unincorporated towns of Washington County, Wisconsin, Chapter 275's floodplain article regulates all land shown on the FEMA Flood Insurance Rate Map as Zones A, AO, AH, A1-30 or AE. The county divides that mapped floodplain into four zoning districts, floodway, floodfringe, general floodplain and flood storage, each carrying different development standards administered by Planning and Parks.
Washington County Floodplain Zoning Districts
Some RestrictionsWashington County Code § 275-14A, C(2)(a), D(2)
Areas regulated by this chapter shall include all lands in the unincorporated limits of Washington County, Wisconsin, that would be covered by the regional flood identified as Zones A, AO, AH, A1-30, AE, on the Flood Insurance Rate Map. ... The "Floodway District" consists of the channel of a river or stream and those portions of the floodplain adjoining the channel that are required to carry a...
Flood Elevation Requirements
Washington County, Wisconsin defines flood protection elevation as 2.0 feet of freeboard above the regional flood, and Chapter 275 makes new residential construction in the Floodfringe District meet that mark. In the unincorporated towns, new homes and manufactured homes must have their lowest floor elevated to or above that 2-foot freeboard on fill.
Washington County Flood Protection Elevation
Some RestrictionsWashington County Code § 275-2, § 275-16C(1)(a)
FLOOD PROTECTION ELEVATION An elevation that corresponds to a point 2.0 feet above the regional flood. (Also see "freeboard.") ... All new construction, including placement of manufactured homes, and substantial improvement of residential structures, shall have the lowest floor elevated to or above the flood protection elevation on fill. The fill around the structure shall be one foot or more a...
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