Stormwater manuals

Our stormwater manuals provide stormwater permit implementation and management guidance. Contact your municipality or permit administrator to determine which manual you need and for questions regarding implementation of stormwater management guidance.

Ecology's Stormwater Management Manuals (SWMMs)

The dropdowns below provide access to past and present SWMMs.

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​Emerging guidance

Stormwater management is evolving. As such, stormwater management guidance documents are often published in between versions of Ecology’s SWMMs. Stormwater management guidance documents released after publication of the latest SWMMs are provided in the “Additional Resources” folder within the interactive online version of the SWMMs. Direct links are provided below:

Preparing for our 2024 SWMM updates

We anticipate publishing the next version of our SWMMs in July of 2024. Listed below are the steps taken so far:

Equivalent regional stormwater manuals

In some cases, municipal stormwater permittees have the option of either adopting portions of the appropriate Ecology Stormwater Manual or portions of a regional manual determined to be equivalent to the Ecology Stormwater Manual.  For more information, visit the equivalent stormwater manuals for municipal stormwater permits webpage.

Other references for stormwater management and design


Ecology webpage links