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.

Stormwater Manual Updates

The stormwater manuual has been updated based on stakeholder feedback and revised requirements from the Department of Environmental Quality. Changes 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 updated manual was available for public comment from April 30 to May 30, 2025 and approved by Council in January 2026. Below is the final 2026 manual, including a summary of changes and a table of manual reorganization from the 2020 version: