Pacific Rivers
Central Oregon's Bridge Creek, a 45-kilometer-long tributary to the John Day River, is an extensive BDA test project that started implementation in 2009, over 14 years ago. There is a long and storied history of beaver removal at the site: in the 1820s, English trappers deliberately exterminated the region's beavers to dissuade U.S. trappers from invading the Oregon Territory, which was claimed at the time by both the United Kingdom and the United States. The gambit failed, but the beavers' destruction, combined with unchecked cattle grazing, have left an enduring legacy. Without the beaver dams to slow the flow and encourage sediment deposition, Bridge Creek devolved into a narrow trench bordered by dried out pastures.
Despite its grim appearance, Bridge Creek continued to support a small population of endangered steelhead— rainbow trout that, like salmon, migrate to the ocean and back. A skeleton crew of beavers had also survived, although any dams they built across the sluice-like channel tended to wash out during bigger storms.
In the mid-2000’s, scientists had been documenting the amounts of sediment trapped behind beaver dams and thought that ​creating those conditions in Bridge Creek could have a profound benefit on the degraded channel, reconnect it with the floodplain, and inundate side channels and backwaters in which juvenile steelhead could thrive.
In 2009, a hydraulic post-pounder was used to build 76 BDAs, built to mimic the function of natural beaver dams with on-site building materials (such as wood, turf, mud, and cobble), and can be reinforced with wooden posts. Beavers soon returned to the site and went to work. By 2013, monitoring showed that beavers had fortified nearly 60 of the BDAs and built 115 new dams (Silverman et al. 2019). This combination of constructed and natural beaver dams can create widespread benefits at relative low-cost per area restored (Bouwes et al. 2016; Weber et al. 2017). The overarching goal was to convert a drastically simplified stream into a complex one. With the brilliant, natural ecological engineers at work, their dams slowed the water, and the stream bed began climbing out of its trench, spilling water onto floodplains. The creek's submerged area tripled, and side channels grew by more than 1,200% in just a matter of a few years.
Steelhead soon took advantage of the renewed habitat. Bridge Creek produced nearly three times more fish than a nearby control stream, and its young steelhead were 52% more likely to survive, the researchers reported in 2016 in Scientific Reports (Bowes et al.). Other studies found the dams and ponds actually helped moderate water temperature spikes, by allowing water to percolate through the gravel and streambed sediment.
​Projects like this, with nearly 10 years of monitoring, are incredibly valuable. Lessons learned along the way will inform efforts and decisions on subsequent projects and provide optimism that inexpensive efforts can have big impacts, and reverse declines that lasted decades.
