Portage County, WI Environmental Rules: Erosion Control (2026)

Portage County Code § 7.4.6(4) requires the subdivider of a major subdivision, county plat, or minor subdivision to submit a storm water management plan to the Planning and Zoning Department, timed to the sketch plat submission, before construction disturbs the site. Subsection (a) requires the plan carry the signature and seal of a registered professional engineer unless the Department authorizes otherwise, and a professional engineer or certified surveyor must oversee installation of the storm water features shown on the approved plans; the subdivider remains responsible for building to the approved design until 'as built' conditions are certified and accepted by the governing town and county.

Beyond the county's own review, § 7.4.6(4)(a) folds in a state floor: the development must also meet the construction-site and post-construction performance standards of Wisconsin Administrative Code ch. NR 151, plus any other applicable state or federal requirement, written into the plan the county reviews. Section 7.4.6(4)(b) adds design substance, directing the runoff-control plan to account for site conditions such as steep slopes, high water tables, and shallow soils, to size facilities like diversions, detention and retention ponds, and infiltration basins to a 25-year storm event using a minimum runoff curve number of 60, and to favor low-grade side slopes in basin design for public safety.

The same Improvements article separately requires surface water management under § 7.4.6(6) for the prevention of erosion and flooding, again submitted at the sketch-plat stage. A plat found unsuitable for building because of soil conditions cannot be approved unless the applicant wins an appeal under § 7.9.2(3).