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.

Order a hard copy or CD

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.

​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 SWMMWW and SWMMEW in July of 2024. The anticipated timeline for the update process:

  • Fall 2021: We hosted an open house regarding proposed consistency updates to the SWMMs. 
  • February 2022: Early input was given to Ecology by SWMM stakeholders.
  • Spring 2022: We hosted listening sessions regarding early thoughts on proposed SWMM updates.
  • Fall 2022: We will provide preliminary drafts of select SWMM sections for informal public comment.
  • Summer 2023: We will provide formal drafts of SWMMs for formal public comment.
  • July 2024: Publish the 2024 SWMMs.

Other references for stormwater management and design


Ecology webpage links