Stormwater Management Manual

The City’s Stormwater Management Manual (SWMM) provides guidance and standards for the placement, design, and maintenance of structures used to control runoff, reduce flooding, and prevent pollution from contaminating our local waterways. The manual applies to stormwater management design for public and private development and redevelopment within the City of Lake Oswego. 

Spring 2025 Updates

We are revising the manual to incorporate stakeholder feedback and revised requirements from the Department of Environmental Quality. Major updates include:

• reordering of the manual on some core content,
• removing educational information that didn’t relate to design,
• adding facility hierarchy table/criteria required by the new permit,
• changing how offsite discharges are treated.

The SWMM will be available for public comment in mid-late April. Stay tuned for more information and the draft of the SWMM. 

Current Manual 

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

Previous Manuals 

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