Floodplains In Portland
Historically, floodplains in the Willamette River basin were complex and had a natural ability to absorb and diminish floods. Streams were a braided series of small side channels that changed and rearranged each year. Salmon spawned and spent their first few seasons of life in these side channels. Beaver ponds were abundant and created wetlands for a diversity of fish, waterfowl, reptiles, and amphibians. Wetlands fed by groundwater and springs provided rich soil nutrients and cool, clean water to the streams. There was little development in the floodplain so flooding did not cause extensive damage.
Today, we have lost many of the original wetlands and floodplains that existed before development. Much of this development hugs the edges of our rivers, streams and sloughs and levees have eliminated areas that absorbed floodwaters. Floodplains have been stripped of their native vegetation, drained for agriculture, filled to accommodate development, and covered by pavement for transportation. Increasing stormwater runoff from impervious areas, and less available storage in the floodplain cause more frequent and larger floods in watersheds not protected by levees.
Although we will never be able to reclaim all of the City's floodplains, some restoration can provide safety and environmental improvements. The City of Portland has a strategy to protect citizens and natural resources. Here are some of the things we’re doing: