Portland, Oregon’s Flood Protection Success Story: Reducing Flood Risk and Restoring Floodplains along Johnson Creek.


In February I had a great opportunity to visit a few of Portland, Oregon’s floodplain restoration sites along Johnson Creek.  My visit came a month after Portland experienced major flooding back in January 2012 when record snowmelt and heavy rains flooded many neighborhoods throughout the city.

Seven major floods occurred on Johnson Creek in the last 35 years, and 28 since 1941. However, it was both flooding and water quality issues that put Johnson Creek basin on the top of the City’s priority list. Located on the southeast side of Portland and on the eastern side of the Willamette River basin, Johnson Creek flows 26 miles west through six different jurisdictions and finally into the Willamette River. Although just a small portion (6 %) of Portland’s “100 year” floodplain is in the Johnson Creek watershed, it accounts for the majority (78%) of Portland’s repetitive flood loss claims.

So what has contributed to the repetitive flood damages over these years?  While the Portland area receives roughly 37 inches of rain per year, storms alone can’t be blamed for the damages.  During the Depression Era in the mid-1930’s the federal government sponsored a “flood control” project that allowed the state to deepen and straighten sections of a 15 mile stretch of Johnson creek and line some areas with rock boulders or ‘riprap” and dikes to contain high flows. In addition to these activities that caused the river to flow higher and faster and impacted the wildlife habitat, more commercial, residential and industrial development moved into the floodplain and into harm’s way.

Ready to tackle flooding and water quality issues, Portland’s Bureau of Environmental Sciences “BES” released the Johnson Creek Restoration plan in 2001 to strategically target areas and practices that could best store and convey floodwaters naturally to minimize damages from frequent flooding, increase water quality, and restore fish and wildlife habitat.

Critical to the success of the Johnson Creek Restoration plan is Portland’s land acquisition plan of 1997 that helps to grant land acquisitions to willing sellers. To date the combination of local, regional, and federal resources has allowed the city to acquire more than 260 acres and move 90 homes out of harm’s way of flooding.  That same year BES constructed the Brookside Wetland, the first floodplain restoration project on Johnson Creek. The 14-acre wetland can store up to 20 million gallons of flood water and provides habitat for fish and wildlife, clean water, and recreation.

More recently, the City rolled out Portland’s Watershed Management Program in 2005 that allows the city to plan on a watershed basis and the “Grey to Green” program in 2008 that supports stormwater management techniques such as removing or retrofitting fish passage barriers and culverts, planting trees, acquiring land, and increasing the number of eco-roofs that improve watershed health, reduce flooding and increase clean water.

In 2007 Portland completed the Schweitzer Restoration Project (shown in the photo) providing 74 acre feet of flood storage to the Johnson Creek floodplain – that’s enough to cover the 30-acre site with about two-and-a-half feet of water. The restoration also adds cold water spawning and rearing habitat for Steelhead, Cutthroat trout and Coho salmon.   

Last January when Portland received one of the top 20 storms, citizens along Johnson Creek for the first time didn’t have costly damages. The Johnson Creek Restoration effort is a great model for how a city and its citizens can invest in their “natural defenses” and manage floods in a way that both protects people and the environment.

My thanks to Maggie Skenderian, Portland’s BES Johnson Creek Watershed Manager, for sharing her knowledge of the Johnson Creek Restoration Plan and for the on the ground tour of the floodplain restoration sites.   

References
No Adverse Impact Case Studies by the Association of State Floodplain Managers [PDF]
Portland’s Bureau of Environmental Service’s Johnson Creek webpage
Portland Oregon’s Grey to Green Initiative
USGS Video link: Connecting flood management and salmon habitat improvement, Johnson Creek Schweitzer Natural Area, Portland, Oregon