ONLINE OPEN HOUSE - Fall 2017
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 neighborhoods and parks, around businesses and under roadways, and then join together at the intersection of Walker Road and Murray Boulevard in Beaverton.
Over time, changes to human activities and rain patterns have altered the way water behaves on the landscape:
- Streams were altered, and wetlands were drained for new human 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 green 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.
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.
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.
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.
A collaborative approach to flood management
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 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. This 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
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.
Flood remediation collaborative partners
- Beaverton Chamber of Commerce
- City of Beaverton
- City of Portland, Bureau of Environmental Services (BES)
- Clean Water Services (CWS)
- National Marine Fisheries Service (NMFS NOAA)
- Nike, Inc.
- Oregon Department of Environmental Quality (DEQ)
- Oregon Department of Transportation (ODOT)
- Regional Solutions, Office of the Governor
- Reser’s Fine Foods, Inc.
- Tualatin Hills Park & Recreation District (THPRD)
- Tualatin River Watershed Council
- Tualatin Soil and Water Conservation District
- Washington County
- Wetlands Conservancy
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.
Do you live in a floodplain?
Check the Federal Emergency Management Agency website to learn if you live in a designated floodplain.