Dam dimensions and surface porosity affect the water storage capacity of beaver dam analogs and natural beaver dams

Abstract Introduction Widespread anthropogenic stream incision in the western United States necessitates effective restoration strategies. Beaver dam analogs (BDAs) have emerged as a popular tool for restoration, yet their hydrological performance relative to natural beaver dams remains understudied. Objectives This study compared water retention by BDAs to natural beaver dams and undammed references, with a focus on how dam dimensions affect hydraulic performance. Lower water velocities (indicated by longer water travel time [WTT] or hydraulic residence time [HRT]) could promote nutrient and sediment retention. Water storage in pools can provide a critical resource for wildlife and influence thermal regimes for aquatic species. Methods This study was conducted across eight watersheds in Washington State and two in Idaho. We measured pool volume and HRT of BDAs and natural beaver dam impoundments and WTT for stream reaches with and without BDAs. We used linear regression and ANOVA (Analysis of Variance) to test relationships between dam structure and water storage. Results BDA WTTs were longer than those of reference sites, while natural beaver dams exhibited higher HRT and pool volumes than BDAs. Dam thickness, height, and type were the most influential predictors of HRT. Among BDAs, height and porosity significantly affected HRT. Natural beaver dams stored significantly more water than BDAs. Conclusions While BDAs retain water more effectively than undammed reaches, they fall short of retention by natural beaver dams. Dam dimensions and porosity strongly influence BDA performance, underscoring their importance in improving hydraulic outcomes.