Flooding

The Cedar Mill Creek / North Johnson Creek Watershed

Cedar Mill Creek and its tributary, North Johnson Creek, drain 5,300 acres from the West Hills into Beaverton Creek in the Tualatin Hills Nature Park. These creeks pass through neighborhoods and parks, around businesses and under roadways, before joining together at the intersection of Walker Road and Murray Boulevard in Beaverton.

Humans have been changing stream flows in the Cedar Mill Creek / North Johnson Creek watershed for nearly 200 years.

An aerial view of Beaverton businesses and homes near a body of water

Human activities and rain patterns have altered the way water behaves on the landscape:

  • Streams were altered and wetlands were drained for early logging, farming and other development
  • Homes were built in historic floodplains before regulations existed to prevent it
  • Urban growth, roadway construction and reduced natural space has affected the land’s ability to absorb rainfall before it enters streams

These changes have resulted in flooding, especially at lower elevations.

The Cedar Mill Creek Flood Remediation Collaborative was a partnership of agencies, businesses, and other interested organizations in Washington County that worked together as a Project Team to address flood risks while providing high-quality natural habitat within the Cedar Mill Creek and North Johnson Creek corridors. Oregon Solutions guided this effort by bringing  stakeholders together to better understand local flooding and reach agreement on how to work together to address these issues.

The Project Team was supported by technical experts who helped to develop a thorough and collaborative way to address flood risks and improve drainage for this area. Representatives from all the Collaborative jurisdictions and organizations reached out to property owners in the watershed. Open houses and meetings were held, so the representatives and community members could talk one on one. 

People submitted photos of flooding and shared their experiences with eroding creek banks, falling trees and flood insurance.  The Collaborative utilized that background information when it developed potential strategies that could be implemented to mitigate the flooding and preserve the integrity of the watershed.

Cedar Mill Creek Flood Remediation Collaborative Goals

  • Create an approach that minimizes or mitigates flooding impacts while considering economic development, habitat value and quality of life concerns.
  • Develop a plan that can be phased.
  • Identify funding sources.
  • Consider how multiple agencies’ regulations can be addressed in a way that results in the greatest possible good for the public and for the ecosystem, i.e., a basin-wide assessment approach.

Members of the Collaborative

  • Beaverton Chamber of Commerce
  • City of Beaverton
  • City of Portland, Bureau of Environmental Services
  • Clean Water Services
  • National Marine Fisheries Service
  • Nike, Inc.
  • Oregon Department of Environmental Quality
  • Oregon Department of Transportation
  • Regional Solutions, Office of the Governor
  • Reser’s Fine Foods, Inc.
  • Tualatin Hills Park & Recreation District
  • Tualatin River Watershed Council
  • Tualatin Soil and Water Conservation District

Whether upstream or downstream, all residents and businesses within the Cedar Mill Creek/North Johnson Creek watershed will have a shared role in flood management efforts. Search for your address to find your place in the Cedar Mill Creek/North Johnson Creek watershed.

Watershed Enhancement Team

This flood remediation effort will require long-term collaboration among public agencies, private businesses, community groups and residents.

On Oct. 9, 2018, a Declaration of Cooperation identifying processes for management and flood mitigation was signed by members of the Collaborative. This declaration provides a roadmap to address this long-standing problem and recognizes that the challenges within the watershed are not within one organization's responsibility or ability to influence.

Subsequently, the Watershed Enhancement Team (WET) was formed to collaboratively address flooding and watershed management throughout Washington County. The Cedar Mill Creek / North Johnson Creek watershed is WET’s first project.

WET is evaluating the flood remediation/watershed management strategies compiled by the Collaborative for inclusion in a three-year work program. These strategies fall into two areas: Policies and Programs, and Structural Projects. 

Policies and Programs

The policies and programs could increase the community’s flood resiliency. Key elements include:

  • Flexibility to focus strategies on specific areas or basin-wide, as appropriate
  • Typically lower costs than infrastructure projects
  • Encouraging property owners to participate in flood mitigation efforts, on individual properties and in the larger community

Reduced rate flood insurance: Programs that would allow qualified property owners to apply for flood insurance at a reduced cost.

Washington County and the City of Beaverton could help residents receive more affordable flood insurance through the Community Rating System National Flood Insurance Program.

  • The program can provide reduced flood insurance premiums for properties within or adjacent to a regulated floodplain.
  • The premium reduction amount grows as the “rating” of Washington County and the City of Beaverton improves.
  • The County and the City can receive a better rating for completing tasks that help mitigate flooding, such as providing public information about flooding or updating local flood data.
The National Flood Insurance Program logo.

Community education and technical assistance: Programs to help community members prepare their properties for more resilience to flood impacts and provide opportunities to contribute to flood management strategies.

  • Community education programs make information accessible and help improve understanding and stewardship throughout the drainage area.
  • Technical assistance helps property owners manage flood risk through flood proofing, flood elevation certificates or flood insurance consultation.
  • Potential partners include local governments, non-government organizations and conservation districts.
  • Effectiveness depends on the level of community participation. The more community is involved, the more effective the programs will be.
Community members pose for a photo at a volunteer event.

Creek corridor land management: Programs to potentially help control activities near creeks.

  • Purchase of property or easements near creeks to keep floodplains clear of development or enable future structural projects such as retention ponds.
  • Develop additional policies to help control the types of development or redevelopment near creeks, such as increased buffer zones or mitigation requirements.
A bird’s-eye view of a creek corridor flowing between urbanized areas.

Structural Projects

The structural projects are strategies that help manage flooding by building or enhancing public infrastructure along stream corridors. Key elements include:

  • Projects scattered throughout the basin that provide benefits to affected neighborhoods
  • Typically led by public agencies
  • Limited locations are available for structural projects

The Project Team reviewed an inventory of planned capital projects that are already funded to evaluate add-on opportunities. The project team is also considering potential new structural projects.

Conveyance: Projects that help move water downstream more quickly.

  • Promotes neighborhood drainage
  • Retrofit conveyance in existing neighborhoods
  • Consider the risk of moving flooding problems downstream
Water flows through a culvert beneath the ground.

Storage/detention: Projects that hold flood water in a controlled area and release it slowly.

Water storage is usually held within creek corridors, and is referred to as in-line storage.

  • Retrofit existing storage in neighborhoods
  • Explore if new storage level controls may be an option to drain water before large rain events
  • Improve local habitat as part of storage project
  • Consider difficulty to maintain fish passage with in-line storage projects
A pond that acts as a water detention area after rain events.

Sediment removal: Projects that increase the amount of water that can be stored in streams by removing fine sand and mud that builds up over time.

  • Interrupts the natural process of landscape evolution
  • Not sustainable but may be temporarily useful for water, or sediment storage
  • Would require periodic site disturbance with ecological risks
  • Requires challenging permit processes
  • Can be costly relative to benefits

Natural resource enhancement: Restoring natural areas like wetlands to absorb flood water.

  • Requires large amounts of land relative to expected flood reduction
  • Focuses on ecosystem health and long-term flood resilience
  • Intermediate cost compared to other structural projects
NaturalResource.jpg

Community

Public meeting materials

We held a public meeting on Aug. 1 at St. Andrews Lutheran Church on Butner Road to share information and collect feedback from community members. The meeting was open house style where community members could drop in and talk to staff about potential strategies to enhance the natural functions of Cedar Mill Creek and North Johnson Creek corridors and manage flood risks to residential and commercial properties. 

Project Team

Project Team meetings and documents

  • Summary