With funding provided by the Bonneville Power Administration (Project 2003-017) and by the National Oceanic and Atmospheric Administration, Northwest Fisheries Science Center (NWFSC) conducted a study in Bridge Creek, Oregon which exemplified the positive impact that stable beaver colonies can have on a river ecosystem, specifically their impact on habitat for steelhead.
From their study:
Stream incision is a widespread problem that results in substantial degradation of both aquatic and riparian habitats. Mechanical restoration of incised streams is expensive. Although incised streams may return to an aggraded condition naturally over time, this process can take centuries. Our study provides evidence that some incised streams can begin to aggrade more quickly through the use of flow obstructions that reduce stream power, allowing sediment to accumulate on the streambed and floodplain while also reducing bank erosion. Beaver and vegetation are essential to this accelerated recovery.
We are assisting a small, extant beaver population to restore geomorphic, hydrologic, and ecological function in the Bridge Creek drainage. By helping beaver create stable colonies, which will aggrade the incised reaches of Bridge Creek, we are achieving measurable improvement to riparian and stream habitats. These improvements should translate to increased abundance of steelhead.
Initial monitoring of steelhead density and survival has been encouraging. We will continue monitoring to assess the geomorphic and biological changes occurring at individual structures and reaches. Continued monitoring will allow a full assessment of restoration effects from beaver dam support structures and will guide us in modifying our structure design as needed to continue these improvements.