American Rivers explored Portland, Ore.'s flood protection strategies in a recent blog post. According to the post, seven major floods have occurred on Johnson Creek in Portland, Ore., over the last 35 years. 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.

Post author Shana Udvardy writes that while the Portland area receives roughly 37 in. of rain per year, storms alone cannot be blamed for the damages.  During the Depression Era, 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.

According to American Rivers, the city of Portland has implemented several programs and projects to tackle these flooding and water quality issues:

-In 2001, Portland’s Bureau of Environmental Sciences (BES) released the Johnson Creek Restoration plan 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.

-In 2005, the city rolled out Portland’s Watershed Management Program that allows the city to plan on a watershed basis.

-In 2007, Portland completed the Schweitzer Restoration Project providing 74 acre-ft of flood storage to the Johnson Creek floodplain----enough to cover the 30-acre site with about 2.5 ft of water. The restoration also adds cold water spawning and rearing habitat for Steelhead, Cutthroat trout and Coho salmon.   

-In 2008, the “Grey to Green” program was implemented. It supports storm water 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.

Source: American Rivers