If you're planning a development project in Des Moines, there's an important update to be aware of. As of July 1, 2026, the City has officially adopted the 2026 King County Surface Water Design Manual (KCSWDM) as the current standard for stormwater design.
These updated standards help ensure new development continues to protect our streams, neighborhoods, and environment by using the latest stormwater management practices.
What Does This Mean for Existing Projects?
Projects that were permitted before July 1, 2026, may still be able to move forward under the standards that were in place when they were approved—but only if construction begins within the applicable vesting period.
If construction does not begin before the project's vesting deadline, the plans will need to be updated to meet the requirements of the 2026 KCSWDM (or any future version required by state regulations). Any revisions must be reviewed and approved by the City's Surface Water Division.
For vesting purposes, construction is considered to have started once site work has progressed to the point where rough grading is complete or utilities have been installed. Rough grading is considered complete when the site is within one foot of the final approved design elevations.
If you have an upcoming project or aren't sure how these changes may affect an existing permit, the City's Surface Water Division is happy to help answer questions and provide guidance before work begins.
2026 KCSWDM