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Loss of beaver dams decreases floodplain connectivity in Colorado headwater streams

Schultz, Kayla1; Rathburn, Sara1; Mertz, Connor1; Morrison, Ryan R.1

Published May 28, 2026 on Dryad. https://doi.org/10.5061/dryad.2z34tmpzd

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Abstract

As ecosystem engineers, beavers (Castor canadensis) modify river corridor form through dam building. When beavers are removed from a system, their unmaintained dams wash out, altering the stream’s hydrologic regime. We quantified the change in floodplain connectivity caused by the loss of beaver dams at three headwater tributary sites in the Kawuneeche Valley, Rocky Mountain National Park, Colorado, USA. From field observations, we developed two-dimensional steady-state hydraulic models to compare metrics of floodplain connectivity under historical (beaver-active) and present (no beaver activity) scenarios. The historical scenarios featured modeled beaver dams matching conditions in the year 1990 when beavers were present in the landscape. We simulated three low-to-moderate recurrence interval flood discharges to assess floodplain connectivity metrics, including the volume of water on the floodplain, the fraction of flow moving through the floodplain, the volumetric flux into the floodplain, and mean site and floodplain residence times. We found that the loss of beaver dams decreases floodplain connectivity across all connectivity metrics (up to a 96.5% loss in connectivity) except mean floodplain residence time, which increased in the absence of dams. Channel velocities also increased following the loss of beaver dams. We conclude that, in headwater streams, beaver dams play an important and quantifiable role in facilitating floodplain connectivity, and floodplain disconnection from the loss of dams has major implications for other ecological and geomorphic floodplain processes.