Why do I need an erosion permit? FAQ

Why do I need an erosion permit?

The Erosion Prevention program is part of the City’s Comprehensive Stormwater Management Plan which addresses federal water quality mandates and sets local policies to protect stormwater related waterways. These include the Mill Race, Amazon Creek and the Willamette River in addition to open drainage ways, creeks and wetlands. Construction sites can be a major source of stormwater pollution if not managed correctly. Part of the erosion permitting process is the development of a “Construction Site Management Plan,” which identifies ways to minimize impacts to water quality and natural resources during construction.


An erosion prevention permit is required prior any site disturbance for construction activities that:

  • Disturb an area one acre or greater in size or
  • Disturb 500 square feet or involve the excavation or placement of 20 cubic yards of material within a sensitive area

A site is considered a sensitive area if it meets any of the following criteria:

  • The slope of the parcel is greater than 10%:
  • The site contains highly erodible soils
  • The parcel or tax lot of record has the potential to directly drain into a water feature or its designated buffer area.

Projects not required to obtain an erosion permit are still required to meet outcomes. A reference map of sensitive areas is located at the Permit and Information Center.