Design & Construction Standards Update

On April 22, 2019, the current Design & Construction Standards, (R&O 19-5) went into effect. R&O 19-5 includes changes to stormwater management standards to meet the requirement of CWS’ Watershed-Based permit and address the effects of hydromodification. R&O 19-5 was adopted this spring to meet permit requirements, and additional updates (Fall Amendments) are currently being proposed for consideration by the Board on November 12, 2019. The proposed Fall Amendments are now available for public review and comment.

Proposed Fall Amendments for Public Hearing

Information added October 31, 2019

The proposed Fall Amendments focus on updating standards for consistency with current technology and construction practices, and improving system operations and maintenance. A redline version of the Preliminary Draft is available for review and each chapter includes Reader Notes to describe the purpose of all substantive changes. Reader Notes are not included for minor formatting and grammar updates, though they are shown in redline formatting.

CWS encourages interested stakeholders to review the proposed revisions to the Design & Construction Standards:

Information added October 31, 2019

Written comments are welcome at any time, but should be submitted prior to October 25, 2019, in order to be considered for inclusion in the final draft for Public Hearing. Please submit questions and comments to

Testimony may be submitted during the Public Hearing at 6:30 pm on Tuesday, November 12, 2019. Please sign up to get information and updates direct to your email.

Archived Documents and Context

Design & Construction Standards – R&O 19-5
Information added September 30 and October 8, 2019
Information issued April 4, 2019

CWS encouraged interested stakeholders to review the following documents and tools:

The following documents, released in January, remained applicable as of this date:

Information issued March 29, 2019

CWS has developed additional language changes to address two areas in which the Board expressed interest during the March 26 public hearing. Those two areas are:

  • Impervious Surface Area to be used in calculating facility size serving developments with lots 3000 sf or smaller
  • Evaluation Criteria for requests to allow a pond depth greater than 5 feet

Additional Staff-Recommended Language Changes to Sections 4.08.1 and 4.09.2 (PDF 140KB).

Information issued March 27, 2019

During the March 26, 2019 Board meeting, staff recommended making several minor changes to the Proposed Chapter 4 that was posted on March 14, 2019.  These revisions included:

  • Infill Exemption Analysis (Section 4.03.7.a.5.D): clarify exclusions of “remaining developable area”
  • Allow for street trees to get Stormwater Tree credit (Section 4.09.15.c.3)
  • Clarify Impervious Area used for remodels, additions, etc. on existing single family lots (Section 4.08.1.b)
  • Pond Orifice Sizing: address possible conflict between co-implementer standards (Sections 4.09.2.c.8, 4.09.5.b.6, and 4.09.6.b.5)
  • Underground Detention
    • Add inspection ports and manholes (Section 4.09.3.c.2.d)
    • Require approval by road owner and maintainer (Section 4.09.3.c.3)
  • Vegetated Swale: 3’ max. ponding depth (Section 4.09.3.c.3)
  • Fix copy/paste error in Section 4.03.2

The Board directed staff to make these changes and post them for public review. 

Proposed Chapter 4, including revisions directed by the Board at the March 26 Public Hearing (PDF 468KB).

Information issued March 22, 2019

Since the release of the Preliminary Drafts of Chapters 1 and 4 on February 14, 2019, CWS has received many comments, suggestions and questions regarding the proposed changes. Staff has worked diligently to incorporate these comments into a Proposed Draft of the Design & Construction Standards. Updates to the standards are focused on incorporating requirements for development to address the effects of hydromodification. As such, proposed changes to the standards are focused on incorporating and updating relevant definitions in Chapter 1, engineering plan submittal requirements in Chapter 2, and inserting hydromodification requirements into Chapter 4. No changes have been made to the other chapters. Also included in this release is a memo describing CWS’ proposed approach to addressing the Stormwater Management Fee-in-Lieu charge. While adoption of the Fee-in-Lieu charge is not part of the Design & Construction Standards Update, it is relevant to the Base Strategy. The Fee-in-Lieu charge will be included with the proposed update of the CWS Rates and Charges, scheduled for the Board in June 2019.

CWS encourages interested stakeholders to review the following documents and tools:

The portions of the Complete Proposed Draft of the Standards with redlines are also posted as individual chapters to make review of proposed changes easier:

  • Proposed Draft Table of Contents (PDF, 23KB)
  • Proposed Draft Chapter 1 – General Requirements and Administrative Provisions (PDF, 190KB): added and revised definitions in Section 1.03
  • Proposed Draft Chapter 2 – Administrative Procedures (PDF, 191KB): Updated submittal requirements
  • Proposed Draft Chapter 4 – (March 14, 2019, version) Runoff Treatment and Control (PDF, 462KB): addition of hydromodification standard, and revisions to sizing criteria, infiltration criteria, and design criteria for specific facility types
Information issued February 14, 2019

Documents and tools:

Information issued January 16, 2019

Draft Hydromodification Base Strategy and Methodology

CWS is proposing a variety of stormwater management approaches that can be used at different scales to address the effects of hydromodification including stream enhancement, Low Impact Development Approaches (LIDA) and detention. The combination of approaches used would be based on landscape setting, historic and anticipated development patterns, project size, and stream condition.

A draft Base Strategy and Methodology (PDF, 1.6MB) document was created as a proposal and released January 4, 2019. It demonstrates how applicants can determine what approaches to addressing hydromodification impacts are expected to apply to a development site The Base Strategy utilizes the Hydromodification Planning Tool Web Map (PDF, 2.3MB) to identify key conditions that factor into determining the preferred approach for a particular development site. The methodology document also discusses tools and methods for designing different approaches.

This Base Strategy builds on the existing Design and Construction Standards and addresses the management of runoff volume. A document was created for determining which approaches are expected to apply under the Base Strategy and what tools are available for applicants. CWS is also actively developing more detailed Sub-Basin Specific Strategies to identify region-specific stormwater management approaches based on analysis of local stream and watershed conditions. Examples of Sub-Basin Specific Strategies are those currently available in the North Bethany development area in an unincorporated part of the County north of Beaverton and River Terrace in Tigard.

Since the release of the Base Strategy and Methodology on January 4, there have been several updates and additions, including:

CWS encourages interested stakeholders to review the following documents:

Submit comments to Initial feedback on this topic is requested by January 23, 2019, though comments are welcome at any time.


For meeting announcements and updates join our email list

Send questions or comments to

Damon Reische
Planning & Development Division Manager

Receive news on what we are doing in the community and our innovative solutions to continue on providing clean water.