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The City of Portland, Oregon

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Ave, Suite 613, Portland, OR 97204

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Public comment is requested on proposed changes to Stormwater Management Manual, Title 17.38

Graphic of manual coverEnvironmental Services is accepting public comment on the proposed 2020 SWMM and changes to Title 17.38

Comments accepted until 5 p.m., Friday, June 19, 2020

For more information — Adrienne Aiona at 503-823-2051 or email BESStormManual@portlandoregon.gov

The City of Portland is updating its Stormwater Management Manual (SWMM) and Title 17.38, which the provides the authority for the SWMM, Environmental Services' Maintenance Inspection Program, and the City's Source Control Manual. The City relies on the SWMM to meet regulatory requirements and to protect Portland's watershed resources and infrastructure investments. When each project meets the requirements of the manual, it contributes to important citywide goals to protect watershed health, groundwater resources, rivers and streams, and downstream infrastructure; to control City wastewater treatment costs; and to reduce the risk of sewer overflows and backups.

The City updates the SWMM every few years. This helps keep stormwater policy in step with changing conditions and technology advancements. The SWMM applies to development activities that construct or alter impervious area, some paving projects in the right-of-way, and any parcel-based development on properties.


How can I learn more about the changes?

There are four opportunities to learn more about the changes. Registration is required.

SWMM focused presentations

Presumptive Approach Calculator (PAC) focused presentations

Annotated presentations will be posted here following sessions.

Public hearing cancelled

Environmental Services received no requests for a public hearing, so the public hearing for Thursday, June 4, has been cancelled. Please contact Ivy Dunlap at 503-823-7754 or email BESStormManual@portlandoregon.gov with questions.

How can I comment on the proposed changes?

Environmental Services will accept public comment on the proposed SWMM and proposed changes to Title 17.38 from 8 a.m. Monday, May 18, 2020  through 5 p.m. Friday, June 19, 2020.


What are the goals of the changes?

  • Improve clarity
  • Continue to comply with regulations
  • Increase technical rigor and facility performance

What changes are proposed?

  • New chapter structure. Add chapters to align better with user needs.
  • New hierarchy. Separate decisions about stormwater disposal location from stormwater management facility selection. Currently, these decisions are combined in one decision tree.
  • Changes to triggers and exemptions—
    • Remove the exemption for sidewalk and ADA only projects.
    • Change the definition of pavement maintenance to allow exposing underlying gravel.
    • Requirements to construct stormwater improvements in the right-of-way will no longer be dependent on whether a curb is moved or added.
    • Only require stormwater management for additions to existing buildings, constructed within the existing footprint, to large additions (10,000 square feet or greater).
  • Changes to engineering design assumptions and standards and to the Presumptive Approach Calculator (PAC)
    • Increase the water-quality storm size to 1.61 inches of rainfall in 24 hours.
    • Update engineering design assumptions and facility details, including set pre-development curve numbers, change the infiltration rate of imported media from 2 inches to 6 inches per hour, and modify underdrain configurations.
    • Modify flow control requirements in the MS4 area and require more orifice control to improve feasibility of meeting these requirements.
    • Adjust facility sizing based on the impacts of the above changes with some facilities getting larger and some smaller.
  • Simplified approach. Minor changes to Simplified Approach facilities with minimal impacts to small developments and single-family homes.

When will the changes become effective?

The SWMM will take effect in October 2020. There will be a three-month period where the 2016 SWMM can also be used. Starting in January 2021, the conditions of the 2020 Stormwater Management Manual will be required except for City initiated and public works projects at or past 60% design and building permits that are deemed complete. For more detailed vesting information see the Summary of Changes.