After the dam: Using nature’s blueprint to rebuild a stream

A remote northeast Washington creek is getting its groove back after more than a century, following removal of Mill Pond Dam.

Sullivan Creek flows for 16 miles through forested mountains to the Pend Oreille River. But for 108 years, the creek widened to become Mill Pond three miles upstream from the town of Metaline Falls. The Inland Portland Cement Company built a log crib dam there in 1909, upgraded to a concrete structure a few years later.

A pedestrian walkway now marks the site of the Mill Pond Dam, which

was removed over several months in 2017 and 2018.

Deconstructing a dam

Mill Pond Dam eventually became part of a hydroelectric facility owned by the Pend Oreille Public Utility District (PUD), but it didn’t produce hydropower for the past 50 years. The PUD agreed to surrender its operator’s license and remove the dam to avoid continued upkeep costs, and Seattle City Light took over responsibility to mitigate relicensing of their Boundary Hydroelectric Project.

The Washington Department of Ecology helped regulate the dam’s deconstruction – done in stages over several months in 2017 and 2018 – to reduce impacts on native fish populations, flooding and water quality. Ecology worked on a permitting strategy that put Seattle City Light on a path toward meeting requirements with flexibility for using natural processes to help the stream rediscover its course.

“Sometimes we’re lucky enough to be involved in projects that challenge our preconceived notions and require creative thinking,” said Ecology Project Manager Jacob McCann. “The end result is a win for the Sullivan Creek watershed and a testament to the power of collaboration.” 

Once Mill Pond was drained, engineers designed and constructed a route

for Sullivan Creek to follow. The channel is expected to move over time.

Reconstructing a riverbed

Last fall, a flushed out Mill Pond reservoir left 64 acres of fertile, silty soil primed for a botanical comeback. Seattle City Light has since been working to prevent invasive weeds and establish thousands of native plants and saplings in various clusters across the site.

“Nature doesn’t plant things on eight-foot centers. It deposits seeds in particular places at particular times,” said Lloyd Dixon, the Seattle City Light project manager entrusted with site restoration. “We tried to use nature as an analog as much as possible to create that system of a coniferous forest with a riparian corridor dominated by willows and alders.”

A riparian corridor is the section of floodplain closest to the creek channel. At Sullivan Creek, it’s a work in progress. Engineers first sifted through 100 years of accumulated pond sediment to try and rediscover the original channel and imitate its outlines as closely as possible. They installed logjams along the channel to create scour pools and other features for fish habitat. Woody debris was then scattered across the surrounding floodplain, ready to move with the next high flow and help gently reshape the creek over the coming years.

Moving into the future

“I don’t want to be so pompous as an engineer to say, ‘I’m going to build a channel and it’s going to stay here in perpetuity.’ We know the creek is certainly going to move over time,” Dixon said. “There’s a temporal component to everything that we see out here. But essentially, the stream will mature and the views that we have today will probably be nonexistent in 15, 20 years because of the forest that’s going to grow up around us.”

Guided by nature, and a lot of engineering, Sullivan Creek is learning to make itself at home. Learn more about the project at www.millponddam.com.