Restoring the Wenas Creek Floodplain with Beaver Dam Analogs

11/25/2014  By Darcy Batura - YBFWRB
Lower Wenas Creek is currently in a degraded state. It is impacted by many irrigation diversions and is included on the Department of Ecology’s impaired water quality list based on reduced instream flow and high summer temperatures.  Down cutting of the stream has disconnected the creek from the floodplain, substantially degrading the aquatic and streamside habitats. Incised streams can recover naturally, but the process may take a very long time. This makes it the perfect location for North Yakima Conservation District (NYCD) to pilot the Beaver Dam Analog (BDA) restoration technique. This technique is based upon NOAA's successful work using BDAs in eastern Oregon.

BDAs are biodegradable wooden structures intended to act like beaver dams, which create ponds, slow the stream, and cause sediment to build up, reconnecting the stream with its floodplain. NYCD recently installed 8 BDA’s on one property encompassing more than 2,000 feet of lower Wenas Creek and 10 floodplain acres. The creek is already responding – even under the current low flow conditions! Just two weeks after installation, the creek rose six inches. The real results, however; will be apparent after the higher spring flows allow the BDAs to do their job of trapping sediment and helping the creek bed to rise and activate the floodplain. After the high spring flows subside, NYCD plans to install and additional 2-4 BDAs to fine tune the approach. Clustering multiple BDAs in a defined reach helps to mimic a natural beaver complex. It slows water and makes all of the structures more resilient to peak flows.

“Beaver Dam Analogs have some real advantages over natural beaver dams.” said Brian Schmidt, Natural Resource Specialist with NYCD. “They can be designed to withstand the expected high flows in a particular creek and act as a powerful mechanism for pushing water out onto floodplains. They can also be used to maintain or redirect the main creek channel so that it is intentionally eroding an upstream bank to provide sediment to be trapped downstream, helping to raise the creek level.”

Yakima Basin fish biologists are eager to see the results of the pilot project because this cost effective technique could serve as a model to be applied in many other areas in the basin where it can make stream restoration happen on a faster timeline. The project also builds upon previous work completed in Wenas Creek which has included streamside plantings and fencing, barrier removal and instream flow improvements.

“We hope to develop a programmatic approach to use of BDAs in the Yakima Basin” said Mike Tobin, District Manager with NYCD. “Wenas is a relatively small system, but the BDAs are showing potential to withstand higher flows than expected. Looking toward the future, we may want to explore using this technique for things like side channel enhancement projects on the Naches River.”

Congratulations to the North Yakima Conservation District on the development of a low budget and innovative pilot project with widespread potential application. This project will be an interesting one to watch!

Click here to watch the North Yakima Conservation District & WA Conservation Corps members installing a beaver dam analog. Notice how little the sediment is disturbed in the process.

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