Flooding

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.

Stay informed

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

Thanks for coming!

Thanks to everyone who came to the Aug. 1 open house!

If you couldn't make it, you can still participate online! Learn and share your ideas about strategies to enhance the natural functions of the Cedar Mill Creek and North Johnson Creek corridors and manage flood risks to residential and commercial properties.

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.

Strategies

Proposed strategies to address flooding impacts

The Project Team is considering a range of strategies that could work individually or together to address flooding and flooding impacts in the future. Any successful flood remediation effort will require long-term collaboration among public agencies, private businesses, community groups and residents. We want to know what you think about these proposed strategies and if there are others we should consider.

The strategies under consideration are grouped into two main areas: 1) Policies and Programs and 2) Structural Projects. General information for each strategy is provided below for your information. These concepts will be developed in greater detail after the Project Team adopts a Declaration of Cooperation, providing an agreed-upon framework for participating organizations to address flooding into the future.

Policies and Programs

The policies and programs below offer strategies to increase the community’s flood resiliency through reduced insurance rates, educational and technical assistance, and public policies. The key elements of these approaches 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.

What do you think?

Structural Projects

The structural projects below are strategies that help manage flooding by building or enhancing public infrastructure along stream corridors. The key elements of these types of strategies 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 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

What do you think?

3. We'll need your help in this effort to address flooding. Please indicate your personal level of interest in the following strategies:
Space Cell NoSomewhatYesMore information needed
Are you interested in attending educational programs about flood-related topics?
Are you interested in receiving technical assistance with flood-proofing your home, insurance options, etc.?
Do you think additional limits on development within floodplains is appropriate?
Are you interested in cooperating with partners to install flood remediation structures on your property?
6. What is your property address within the Cedar Mill Creek/North Johnson Creek watershed? (This will help us understand your perspective on flooding issues.)
7. Please provide your name and email address to get updates about local flood management efforts.

What’s next?

Your comments and questions will help shape the Project Team’s Declaration of Cooperation – a document that describes how the partners of the Collaborative will work together to address flooding in the long-term. Read more about next steps.

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. 

You can view boards from the meeting below. Click on a board to enlarge it.

Project Area

How Rivers Work

Our Process

Where We're Working

Potential Non-Structural Program Concepts

Potential Structural Flood Mitigation Concepts

Prioritization Input

How Should We Invest In Our Watershed?

Here's what we heard so far

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. Thank you! 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

History

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 strategies

The Project Team will continue to consider strategies to address flooding issues including existing data and input collected from you and the greater community of stakeholders. 

The Project Team is also working on a Declaration of Cooperation - an agreement to establish a roadmap the participating agencies will pursue to help reduce flooding impacts over time. We expect the Project Team members will sign the Declaration of Cooperation in fall 2018, and we anticipate 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.

This is a long-term process that will take years and commitment from many people. The anticipated schedule includes: 
1.	November – December 2017: Shared Understanding
2.	November – January 2018 Current Projects Opportunity Identification
3.	February – March 2018: Collaborative and Regulatory Opportunities
4.	April – Early June 2018: Potential Funding and Governance
5.	September 2018: Declaration of Cooperation
Spring 2018: Public Input on Potential Options
Fall 2018: Declaration of Cooperation
Winter 2019 onward: Implementation begins

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.