Abstract
The use of beaver dam analogues (BDAs), structures intended to mimic beaver dams, has become popular in river restoration. Within the last decade, annual publications on BDAs have increased by 500% however, robust information on project site parameters and conditions associated with structure “failure” is often under-reported. As a result, there is a lack of knowledge regarding channel geometry and hydrologic metrics associated with BDA implementation and longevity. The constrained geography, spatial scale, and structure design in published research further limits information on the applicability of BDAs across varied hydrogeomorphic conditions. To address this data gap, we summarized important metrics associated with BDA project site parameters and structure design from in-situ measurements reported in published literature combined with publicly available datasets. We also synthesized reported qualitative information on BDA “failure” to highlight common causes. In our review, we found most projects used post-and-weave structures and consisted of fewer than ten consecutive BDAs, spanning less than one kilometer of stream in snowmelt dominated systems in the western USA. Key project parameters varied by more than an order of magnitude among sites (stream power: 30.60-593.09 watts/m2; dam density: 0.001 – 0.083 dams/m2), suggesting variance in ecological outcomes among projects are likely related in part to site characteristics. The beaver inspired structures have been shown to improve aquatic habitat for salmonids, resulting in increased fish productivity and habitat carrying capacity. BDAs may also increase the frequency of surface water availability in intermittent streams by temporarily impounding water and prolonging downstream flow. Within the Columbia River Basin, restoration efforts are often targeted in areas impacted by water abstraction to improve habitat connectivity and quality for Endangered Species Act (ESA)-listed salmonids. As a result, BDAs are becoming a popular restoration tool in these locations. However, the magnitude to which BDAs impact geomorphic and biological processes in intermittent streams has not been well documented. To address this data gap, we applied a before-after control-impact (BACI) study design in a watershed predominantly used for irrigation treated with BDAs. Changes in habitat quantity was measured using pre- and post-treatment imagery and a geographic information system while changes in habitat quality were inferred through changes in fish density and abundances for populations of anadromous and resident rainbow trout (Oncorhynchus mykiss), cutthroat trout (Oncorhynchus clarkii), bull trout (Salvelinus confluentus), and brook trout (Salvelinus fontinalis). Using mixed effects models (LMM), we observed brook trout (p=0.016) and O. mykiss (p=0.036) densities significantly increased in the treatment reach relative to control reaches. Additionally, resource selection analysis revealed pools impounded upstream of BDAs were selected by brook trout and O. mykiss. Increased fish densities combined with increased habitat quantity appeared to lead to greater fish abundance, predominately age 1 fish. Importantly, our observations suggest the use of BDAs may facilitate brook trout, a non-native fish in our study area, and therefore locations selected for BDA restoration should be considered carefully.