In addition to coastal areas, climate change driven by human development impacts the world’s rivers and streams. According to Scientific American, cities across America and around the world have “bulldozed their waterways into submission.” And it’s not just the water running between banks that’s been harmed by humans trying to control them. Below rivers and streams is a layer of water, stone, and sediment called the hyporheic zone that provides nutrients and scrubs pollutants. But one city has successfully restored the critical part of a healthy stream to great success. Seattle’s Thornton Creek was once known as the most degraded creek in the city. Now, Chinook salmon are back spawning in the creek for the first time in decades.

Why This Matters

Restoring urban waterways can create an environment that restores species and broader ecosystems damaged by straightening, damming, and burying streams. It can also reduce flooding hazards: Seattle’s Thornton Creek used to dangerously flood when its old inflexible channels were overwhelmed. Since the project was finished in 2015, the surrounding neighborhood hasn’t flooded. A restored hyporheic zone can also clean up pollutants that flow into the river from stormwater runoff. The 15-foot stretch of the hyporheic reduced the concentration of the majority (78%) of the chemicals by at least half -- a reduction that one researched called “jaw-dropping.”

How They Did It

After securing approval and funding from the city, the creek was widened from its original 4-8 feet to 25-30 feet. Nearly eight feet of gravel and sediment were added to elevate the creek bed to its previous height and recreate its hyporheic zone. Logs were also placed in the streambed to create areas of slower water that would naturally form in a stream.

While the developments in Seattle are encouraging and show that restorations can be successful, the work will ultimately need to scale up for larger streams and rivers.

“Stormwater runoff, biodiversity, flooding -- these are watershed-scale problems,” Paul Bakke, a former geomorphologist at the US Fish and Wildlife Service who worked on the Thornton Creek project, told Scientific American.