Concepts in Action: Restoring Knowles Creek
Charley Dewberry
In the late 1870s, when the first European settlers ferried their possessions up Oregon's Siuslaw River from the coastal town of Florence, many tributaries of the lower Siuslaw including Knowles Creek supported mostly young stands of Douglas-fir and patches of salal and salmonberry. Much of the landscape the settlers encountered had burned in a fire or series of fires during the 1860s. Along the creek stood centuries-old western redcedars described by a traveler in 1853 as the most magnificent stand of cedars on the Oregon coast.
Historical sources suggest that 75,000 to 100,000 coho salmon smolts migrated to the ocean from Knowles Creek spawning gravels each year. A hundred years later, fewer than 1,700 smolts were making that journey. What had been done to make the creek so hostile to salmon survival? And could that change be reversed?
Resource managers with the Siuslaw National Forest, Champion International timber company, and the nonprofit Pacific Rivers Council embarked on a cooperative effort to answer these questions. We began by seeking to understand how water, organic materials, nutrients, and sediment move through the Knowles Creek basin on a time scale of decades to centuries, creating a "digestive" process that develops and maintains salmon habitat. The key turned out to be how frequently landslides and debris torrents deliver sediment to the valley floors and stream channels.
The 20-square-mile Knowles Creek basin is underlain by a bedrock of Tyee Sandstone. Each of the 5,000 hollows in the basin fills slowly with sediment and woody debris, only to release that material in sudden torrents under certain winter storm conditions.
Highly productive flats, built on the lattice of logs and mature trees on the valley floor, hold the key to salmon abundance. When the flats trap and accumulate material from debris flows, they are sites of high biological production.
Settlement caused an accelerating simplification of the stream system. Early settlers cleared logs from the lower 6 miles of Knowles Creek; the latter half of this century saw a burst of road building and logging. By the 1980s, the lower 12 miles of Knowles Creek had cut to bedrock and the water table had dropped significantly. A portion of the water in a healthy stream travels subsurface through gravels and stays cool. With virtually no subsurface flow, water in parts of Knowles Creek reached 75 degrees F during midsummer, fatal to young fish. Salmon populations crashed.
By necessity a restoration strategy is a long-term effort of 50 to 100 years. But the fish cannot wait that long. To increase the digestive capacity of the basin, we embarked on an effort to simulate debris torrent deposits at a few locations in the basin where they would have naturally occurred. To capture smaller pieces and create logjams, we placed large pieces of woody debris at each location. To reset flats downstream at times of high storm flow, most key pieces were not anchored in place.
A severe January 1995 storm gives us hope that we do understand the health of the system. Although smaller pieces of wood surged downstream, our simulated debris torrents were not washed out. All of the jams reset their respective flats, and each flat accumulated 100–150 yards of gravel upstream. The flats captured much of the material transported down the creek. They were beginning to reset the digestive process.
The results are promising but restored only a small portion of the basin's digestive function. The increases are minuscule compared with the digestive capabilities of the basin in a healthy condition. Our strategy is a means of buying time while the replanted cedars of the valley floor grow larger and begin to restore the digestive function significantly.
Thomas C. Dewberry, former restoration coordinator for the Pacific Rivers Council, now works for Ecotrust analyzing, overseeing, and helping to implement various landscape and habitat restoration projects. This essay is adapted from The Rain Forests of Home: Profile of a North American Bioregion.