Cedar Mill Creek flooding

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 your neighborhood and parks, around businesses and under your roadways, before joining together at the intersection of Walker Road and Murray Boulevard in Beaverton.

Over time, human activities and rain patterns have altered the way water behaves on the landscape:

  • Streams were altered, and wetlands were drained for uses like 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 homes, businesses, parks and roads experiencing more flooding, especially at lower elevations.

What we heard from you

We asked you to share your experiences with flooding near Cedar Mill Creek and North Johnson Creek to help inform the work of the Flood Remediation Collaborative.

Stay informed

This collaborative effort will require cooperation from many different parties, including you. Your comments and questions are welcome at any time.

Cars partially submerged in flood water in a residential area

Find your property in the drainage area

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.

What you told us

Here's what we heard

We asked local residents to share their experiences with flooding in a survey from Nov. 14 – Dec. 22, 2017. The map below shows property locations shared by community members and how often they experience flooding.

Here are some highlights of what the community shared:

  • Over 115 responses were collected.
  • Most community members who experience flooding reported one or two flood events per year; About 10 people reported six or more flood events per year.
  • About a quarter of survey participants experienced property damage from flooding within the last 10 years. Many people associated flooding with increased development in the area.
  • Survey participants suggested several ways to potentially address flooding, including:
    • Work with developers to reduce or offset the effects of urban growth on flood management
    • Enlarge culverts and other storm drain equipment and keep clear of debris
    • Maintain streams by removing debris and managing vegetation
    • Restore wetlands and other green space that absorbs water
    • Create reservoirs to capture flood water
    • Educate homeowners about how to manage their property to reduce area flooding

Photos of flooding

Several community members submitted photos of flooding in their neighborhood or on their property, Here are a few of the photos we received:

Homes on Southwest Foothill Drive

Commonwealth Lake Park

Southwest 126th Avenue

Flooding across a fence line


Two hundred years of change

Humans have been changing stream flows in the Cedar Mill Creek/North Johnson Creek watershed for nearly 200 years, starting in the early 1800s with beaver trapping. The loss of beaver dams, followed by logging to support homesteading and related removal of log jams, meant the loss of debris like trees, plants and rocks that normally slowed winter storm flows and allowed the water to spread out and sink into the ground.

Beaver trapping was the start of human changes to local streams (Alfred Jacob Miller’s “Trapping Beaver” 1858; creative commons licensing/ The Walters Art Museum, Baltimore, MD)

The first Anglo-European settlers arrived and settled in the area in 1847. During this time, settlers used creeks to power their cedar mill and water crops. By 1914, lower portions of Cedar Mill and North Johnson creeks had been straightened, and connected wetlands were drained to allow for agriculture. This action moved flood flows downstream into Beaverton Creek. County-wide, the population grew from 2,652 in 1850 to 26,376 in 1930.

New urban development

After the end of World War II, population growth across Washington County took off as county communities became suburbs of Portland. The late 1940s saw the first subdivision built in the watershed at Marlene Village. Until the mid-1960s, subdivisions were located south of the Sunset Highway but by 1970, multiple subdivisions just north of the highway were built in the Cornell and Barnes Road corridors, along with commercial development to support the growing population. In the 1980s and 1990s, development moved northeast into the West Hills; by 2002, most of the watershed had been developed.

Much of this development happened before floodplains were regulated and homeowners had access to flood insurance, which started in the mid-1970s. Nearly all of this development occurred before modern stormwater management regulations were adopted in 1995. Today, regulations and restoration efforts are in place to help minimize impacts of new development on our streams. 

Urban development and streams

The benefits of a naturally winding, plant-populated creek include natural water filtration and resistance to bank erosion. With urban development, several elements of the stream corridor are often changed in ways that can raise flood risks either locally or downstream of the development:

  • As water impervious surfaces like pavement and rooftops increases, rainfall has less chance to soak into the ground, where it is stored in the spaces between rocks in soils and sediments. This water would normally re-emerge in creeks slowly after rain events.
  • Water drainage over developed areas is accelerated due to pavement, gutters, ditches, and storm drain pipes, causing water to reach stream channels faster.
  • Channels are straightened and routed around development, or piped under development, moving water downstream more quickly.
  • Wetlands that normally store water are drained for development, moving more water downstream.
  • In some locations, the stream channel erodes into the streambed, making a narrow, deep channel. While this reduces flood risk, the resulting erosion can result in undercut stream banks that are at risk of collapse.
Members of the collaborative listen to a presentation.

1855 - U.S. General Land Office maps from surveys 1851-1855. Creeks in blue, swampins in green, and Cornell/Barnes Rd. [north] and Walker Rd. [south] in brown

Members of the collaborative listen to a presentation.

1914 - First USGS maps of the basin. These were created by the on-the-ground survey. Channelized portions of creeks highlighted in purple

Members of the collaborative listen to a presentation.

1940-buildings mapped as black rectangles

Members of the collaborative listen to a presentation.

1952-urban development in orange

Members of the collaborative listen to a presentation.

1961-dense urban development in orange

Members of the collaborative listen to a presentation.

1970-development since 1961 in magenta, with 1961-era development in orange

Members of the collaborative listen to a presentation.

2017-current USGS map

Project Team

A collaborative approach to flood management

Members of the Collaborative attend a Project Team meeting

The Cedar Mill Creek Flood Remediation Collaborative is a partnership of agencies, businesses, and other interested organizations in Washington County who have agreed to work 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 is guiding this effort by bringing many stakeholders together to better understand local flooding and reach agreement on how we can work together to address these issues. The Project Team is supported by technical experts who are helping to develop a thorough and collaborative way to address flood risks and improve drainage for this area.

Goals of the collaborative

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

Project Team meetings and documents

About Oregon Solutions

Oregon Solutions partners with the Governor’s Regional Solutions Center to find sustainable solutions to community-based problems by collaborating with businesses, government and non-profit organizations.

Project Team membership

  • 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
  • Washington County
  • Wetlands Conservancy

Next steps

Developing flood remediation options

The Project Team will develop options to address flooding issues considering existing data and input collected from you and the greater community of stakeholders. After assessing the most realistic options based on regulatory, funding and governance considerations, we expect to come back to you in summer 2018 to help us determine the best options.

The Project Team is working on an agreement to establishing a roadmap the participating agencies will pursue to help reduce flooding impacts over time. We anticipate the Declaration of Cooperation will be signed in summer 2018. We expect participating agencies to begin implementing mitigation efforts within the next few years.

This will be a long-term process. We will share a more detailed timeline as work progresses.

November to December 2017: Gain shared understanding of flooding issues; November to January 2018: Identify current projects and opportunities to address flooding through previously planned actions; February to March 2018: Identify new collaborative and regulatory opportunities to address flooding; April to early June 2018: Identify potential funding sources and establish governance responsibilities; late June 2018 partners sign a declaration of cooperation; fall 2018 implement strategies.

Do you live in a floodplain?

Check the Federal Emergency Management Agency website to learn if you live in a designated floodplain.

Stay Informed

Cedar Mill Creek Comment Form

You can request a presentation, ask for information or share your comments at any time using the form below.

If you have photos of flooding in your neighborhood or on your property, upload them here.

Submission of photos indicates consent for public use.