Groundwater‐Mediated Influences of Beaver‐Mimicry Stream Restoration: A Modeling Analysis

ABSTRACT Beaver‐mimicry stream restoration (BMR) involves the alteration of a stream channel to approximate the effects of beaver activity. Project objectives often include increasing groundwater storage and dry‐season streamflow, but limited data are available to understand the nature of its effects on groundwater dynamics. We developed generic groundwater models of mountain headwater streams to investigate the effects of installing a single beaver‐mimicry structure (BMS) using different restoration designs in varied hydrogeologic settings. The magnitude of changes in dry‐season net stream gains from a single BMS was always a minor component of the channel water balance, and would be too small to measure in the field; however, the modeled patterns of change caused by a single BMS help to understand the underlying mechanisms. All tested scenarios caused increases in groundwater recharge from the stream, which resulted in increased groundwater levels, and groundwater outflow from the model domain. For scenarios that did not include evapotranspiration, most treatments in gaining and losing settings caused slight increases in dry‐season net stream gains, but in strongly losing settings net stream gains were reduced. The addition of simulated evapotranspiration often resulted in decreased dry‐season net stream gains, since evapotranspiration increased with groundwater elevations. BMR design and siting influence the types of hydrologic effects that should be anticipated.