Stormwater Manual

In the early 1990's, the Federal Clean Water Act was amended to require select urban areas to have a municipal stormwater (or MS4) permit. In Oregon, this program was delegated to the Oregon Department of Environmental Quality (DEQ). Clackamas County was one of the jurisdictions required to obtain an NPDES permit, and the City of Lake Oswego is one of the 13 co-permittees on the Clackamas County permit. The City of Lake Oswego received their NPDES stormwater permit from DEQ in 1995. The NPDES Permit has subsequently been renewed in 2004, 2012, 2017, and is due for renewal again on March 1, 2022.

The permit requires the City to:
1. Manage stormwater at City facilities and on the City right or way
2. Require stormwater management on private parcels as they develop or redevelop
3. See that stormwater facilities are properly operated and maintained
4. Provide additional oversight for high pollutant-load generating areas (industrial & commercial)
5. Control erosion from construction
6. Control non-stormwater discharges to the storm drainage system
7. Provide public and staff education and outreach around stormwater best practices
8. Provide opportunity for public involvement and participation, particularly at the time of permit renewal
9. Undertake targeted evaluations of specific issues as required by DEQ
10. Monitor the stormwater system; and
11. Report annually on City activities related to the permit. (Recent annual reports are available online.)

Stormwater Management Manual

The 2020 Stormwater Management Manual (SWMM) effective October 1, provides guidance on the siting, design, and maintenance of structures used to manage stormwater from impervious surfaces in the City. The manual applies to stormwater management design for public and private development and redevelopment within the City of Lake Oswego.  The Engineering Department revises the SWMM to meet current regulatory requirements and technical standards.

As part of the final erosion and sediment control inspection, documentation is required from private developers attesting to the stormwater facility’s adherence to the SWMM and an operations and maintenance plan recorded at the County.  Other documentation required of private developers when the facility is an underground injection control is a copy of the DEQ approval of the facility.

  • October 2020 Lake Oswego Stormwater Management Manual
  • October 2020 Lake Oswego Stormwater Management Manual Appendices

The 2016 SWMM and 2016 Appendices apply only to projects submitted prior to October 1, 2020.




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