Olmsted County, MN Environmental Rules: Erosion Control (2026)

20 of the Zoning Ordinance covers any land disturbing activity, defined as clearing, grading, or other disturbance of more than 10,000 square feet of natural cover not tied to general farming. Subdivision B sets the numeric ceilings: the estimated sheet erosion rate during construction cannot exceed five tons per acre per year anywhere in the county's zoning jurisdiction, drops to two tons per acre per year for work inside a shoreland area or within 300 feet of a wetland, and must fall to five-tenths of a ton per acre per year once the project is finished.

The same subsection bars any land disturbing activity from causing ephemeral erosion on a neighboring parcel, from increasing channel erosion in any stream, from leaving unstable slopes after completion, or from depositing sediment on adjoining property, and it requires drainageways to be built and maintained to handle runoff from a 50-year rainfall event. Subdivision C is the permit mechanism: no zoning certificate can be issued and no land disturbing activity can start until the Zoning Administrator approves an erosion control plan, or grants a waiver.

The Administrator may waive the plan only for emergency work needed to protect life or property, minor alteration of a use lawful as of April 15, 1983, expansion of such a use by less than 50 percent of the building's assessed value, temporary uses with no surface water discharge, lots already covered by an approved subdivision-wide plan, or specific low-risk soil types listed in the ordinance's Appendix C. 10: the plan must be consistent with the approved zoning, plat, or conditional use permit, must be reviewed by the township and adjacent city engineer, and must show that the applicant has applied for a National Pollutant Discharge Elimination System permit from the Minnesota Pollution Control Agency.