On Bridge Creek, a tributary to the John Day River in eastern Oregon, scientists with NOAA Fisheries’ National Marine Fisheries Service are installing a series of structures as part of a unique, low-cost approach to stream restoration.

The simple structures provide footholds in the degraded stream channel where beaver can build stable dams and establish colonies.  By partnering with the beaver, the scientists hope to accelerate stream recovery and improve production of the creek’s wild steelhead population, which is part of a larger steelhead population listed as threatened under the Endangered Species Act. 

The simple, cost-effective treatment being applied on Bridge Creek could have far-reaching applications in the Columbia River Basin.

“Bridge Creek is typical of many degraded streams in the western United States,” says Michael Pollock, biologist with NMFS’s Northwest Fisheries Science Center. The creek has been confined to a narrow, incised trench, and high flows rarely reach its former floodplain.  One of the main ways to improve habitat conditions in this situation is to reconnect the stream with its former floodplain.  This helps restore basic geomorphic, hydrologic and ecological functions, and, in turn, create better habitat for steelhead.

The treatment approach on Bridge Creek differs from many conventional stream restoration efforts.  It is attempting to achieve ecosystem restoration goals by actively assisting beaver in the construction of dams.

The goal has been “to help the creek’s beaver population build longer-living dams, but let the beaver do most of the work,” says Chris Jordan, biologist with NMFS’s Northwest Fisheries Science Center.

Bridge Creek supports a small beaver population, but challenges building stable dams have limited the beaver population’s ability to grow and establish new colonies.  Many beaver dams built on Bridge Creek’s incised stream channel have breached or failed, often within the first season, as the full force of spring floods funnels through the channel.

“By building structures for the dams, we are helping beaver change landscapes, and over time that benefits fish,” Jordan says.  

The scientists believe that, if successful, they will be able to achieve their stream restoration goals at much lower cost than if they employed a more conventional approach to stream restoration.

Each structure on Bridge Creek cost between $500 and $1,000 to install, depending on the location, according to Pollock and Jordan.

Beaver provide the rest of the labor and materials for free, and can achieve the same or better outcomes as human-based stream restoration efforts. Conventional techniques can involve massive grading operations using heavy equipment and major revegetation efforts, which can be extremely expensive.   In comparison, the beaver provide a free source of labor and can achieve the same or better outcomes as human-based stream restoration efforts.

NMFS began the treatment in 2009, when scientists installed 84 strategically placed wooden structures on four reaches of Bridge Creek. Many of the structures resembled a simple row of fence posts across the channel and potential floodplain, approximately 0.4 to 0.5 to 1 meter apart and at a height similar to the crest elevation of an active beaver dam.

“The structures were often clustered close together in a stream reach.  This is similar to how a colony of beaver builds a group of dams to form an interactive community and provide protection against predators,” says Jordan. The scientists continue to provide structural maintenance and monitor the results.

The physical response to the structures has been rapid, according to Pollock and Jordan.

“Beaver use of the structures has varied by reach, but overall the beaver have used about 50 percent of the structures,” says Pollock.

Beaver often built dams at the structures within a few months. Some of the dams became part of a larger beaver lodge complex, while others served a temporary purpose.  The structures generally survived their first major floods, and beaver repaired those structures that were damaged.  Many of the structures that did not attract beaver attention also helped improve the stream by providing building blocks that allowed sediment and debris to accumulate. 

There has been “very rapid channel morphology changes as a result of the structures,” Jordan said. Bridge Creek has a high sediment supply, and sediment quickly settled behind the structures during high flows. Many stream sections rapidly aggraded, reconnecting the once incised channel to its former floodplains. This helped spread water across stream-adjacent terraces during high flows, improve groundwater recharge, and support growth of riparian vegetation.

The structures have also improved habitat conditions by forming pools, increasing stream sinuosity, and providing cover for fish.

“This diversity is what drives productivity in a stream,” according to Jordan.   

Monitoring results so far show that steelhead are responding favorably to the changes. Juvenile steelhead are more abundant in the treated reaches, Jordan said. However, he cautions that they will not be able to measure the real response in steelhead numbers until future generations return.  Monitoring also indicates that the structures do not hinder steelhead movement, says Pollock. 

“Tagging studies show that fish are able pass the structures and move up or down the stream,” he says.     

The treatment on Bridge Creek is part of a long-term study conducted by NMFS to restore stream and riparian habitat on lower Bridge Creek.  Scientists are also measuring the physical and biological changes that occur during the restoration. 

NMFS’s efforts build on other projects to improve habitat conditions on Bridge Creek, including those by the National Park Service.

“Over the last four years, the National Park Service has planted 1,000 native cottonwood and willow trees annually along Bridge Creek,” according to Shirley Hoh, resource manager with the National Park Service John Day Fossil Beds National Monument. Increasing riparian vegetation along Bridge Creek will help improve steelhead production and benefit many types of wildlife, says Hoh. 

The efforts are part of a collaborative restoration project between the NMFS’s Northwest Fisheries Science Center, National Park Service, and Bureau of Land Management.  The parties initiated the activities to accelerate natural rates of stream recovery and reconnect the stream to its floodplain, and as a result improve habitat conditions for the creek’s ESA-listed steelhead population. The Bonneville Power Administration provides funding for many of the restoration efforts on Bridge Creek.