Bridge Creek IMW database - Bridge Creek Restoration and Monitoring Project

The incised and degraded habitat of Bridge Creek is thought to be limiting a population of ESA-listed steelhead (Oncorhynchus mykiss). A logical restoration approach is to improve their habitat through reconnecting the channel with portions of its former floodplain (now terraces) to increase both stream and riparian habitat complexity. Using conventional restoration techniques to achieve such objectives can be quite costly, because it involves moving and grading large volumes of fill with heavy equipment that exposes bare ground, and is usually followed by extensive revegetation efforts. Here, we seek a cost-effective, process-based approach to restore geomorphic, hydrologic and ecological functions of this degraded system helping a small, extant beaver population build longer-lived dams. 

Currently, the beaver population is limited because their dams are short-lived. Most beaver dams are constructed within the incision trench and during high discharge events; the full force of flood waters are concentrated on these dams rather than dissipating across floodplains. Consequently most dams breach and fail within their first season. The primary hypothesis we are testing is that by assisting beaver to create stable colonies and aggrade incised reaches of Bridge Creek, there will be measurable improvements in riparian and stream habitat conditions and abundance of native steelhead. The main restoration design challenge is to help beaver build dams that will last long enough to lead to the establishment of stable colonies. If this can be accomplished, the beaver dams should promote enough aggradation to reverse channel incision and reap a number of well documented positive ecosystem benefits associated with dynamic beaver dam complexes that will benefit steelhead and other species.

We are assisting the beaver using an extremely simple and cost-effective restoration treatment. The treatment involves installing round wooden fence posts across potential floodplain surfaces (now terraces) and the channel, approximately 0.5 to 1 m apart and at a height intended to act as the crest elevation of an active beaver dam. This report provides details of the design rationale and design hypotheses employed and summarizes the placement of the 84 BDS structures installed in four reaches in 2009. Additionally, the ongoing monitoring campaign devised to test these design hypotheses is discussed and some preliminary observations from the first year of the campaign are presented. Five variants of the restoration treatment were used; post lines only, post lines with wicker weaves, construction of starter dams, reinforcement of existing active beaver dams, and reinforcement of abandon beaver dams. The biodegradable posts are intended to buy enough time for (1) beaver to occupy the structures and build on or maintain the structures as their own dams, and (2) for aggradation in the slackwaters of the pond from the dam to take place and promote reconnection with a floodplain (terrace). 

Just as with natural beaver dams, individual dams are expected to be transient features on the landscape, expanding and contracting, coming and going as they lose functionality for beaver (e.g. when a pond fills with sediment). The treatment design is geared to saturate four distinct reaches of Bridge Creek with beaver dam support (BDS) structures so that enough potential dams are available to the current beaver population that they can pick and choose the best sites to establish stable multi-dam complexes to support healthy and persistent colonies.
Physical and biological data.

Tags: beaver, bridge creek, depth-temperature sensor, doc/noaa/nmfs/nwfsc, fe (fish ecology) division, national marine fisheries service, noaa. u.s. department of commerce, northwest fisheries science center, oncorhynchus mykiss, or, restoration, stream
Organization: National Oceanic and Atmospheric Administration, Department of Commerce