Flooding on the Nisqually: Same River, New Shorelines

by Addie Schlussel | May 2020

We all know that it’s been an unusual year so far. Even before a virus introduced us to a new world of teleworking and bleach wipes, winter floods had already caused radical changes for the Nisqually and many other western Washington rivers.

Along the Nisqually River mainstem, the Land Trust property that has seen the most dramatic shoreline changes is our Lackamas Flats Protected Area. Back in 1996, flooding here cut a 70-acre island off from the mainland. This island persisted through these most recent floods, but now has a log jam made up of hundreds of logs on its previously open shoreline. Here are pictures from approximately the same spot on the south edge of the island taken in January and March 2020. The first two are looking upstream and the second two are looking downstream.

January 2020 – View upstream from south edge of the Lackamas Flats island.

March 2020 – Stewardship Assistant Courtney peers upstream from her perch on the new Lackamas Flats log jam.

Although difficult for us humans to clamber around, log jams like this one are beneficial to the Nisqually River ecosystem.  Log jams improve habitat quality by creating pools and providing cover. Wood also increases the retention of organic matter and nutrients and helps create islands and new channels. These river features provide additional refuge and habitat, especially for rearing juvenile salmon and trout.

January 2020 – View downstream from south edge of the Lackamas Flats island.

March 2020 – View downstream at log jam deposited during February flood.

Across the river and less than a mile upstream, the flood’s impacts were less positive. Here, one area lost 30 horizontal feet of bank, with the river creeping ever closer to a life estate residence. And just downstream of this area of bank erosion, we now have the opposite problem: too much land. Some of our newly planted native trees and shrubs, including some that are hundreds of feet from the river, are now covered in a foot or more of sand and mud deposited by the river when the floodwaters retreated. Hopefully, some of these plants will tough it out – but many probably won’t.

Further upstream, at the Powell Pastures, we found that the river had shifted east, doubling the size of a gravel beach there and cutting a side channel off from the river. And further downstream, at our Thurston Ridge Protected Area, we found the opposite situation. The side channel along the toe of the bluff there is now deeper and wider than before.

It’s sometimes hard for me to take the long view on this flood when I’m looking at our scraggly baby trees covered in dirt or hearing about the flood’s human impacts. But flooding on the Nisqually is normal. We can see signs of this in the land. The floodplain is marked by countless old channels that the river has abandoned, often by carving a new path during a flood. The Nisqually River has been flooding and wriggling around in its basin for as long as there’s been a Nisqually.

Floods bring challenges and dangers, for sure. But I also feel lucky to work around an ever-changing river—one that will keep surprising us with new twists and turns, new places to explore, and new giant piles of sand.