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Effects of Beaver Dams and Ponds on Hydrologic and Hydraulic Responses of Storm Flows in Urban Streams of the Tualatin River Basin, Northwestern Oregon

Scientific Investigations Report 2025-5039-B
Prepared in cooperation with Clean Water Services
By: , , and 
https://doi.org/10.3133/sir20255039B

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Significant Findings 

American beaver (Castor canadensis) dams fundamentally alter stream hydraulics and hydrology by temporarily impounding water in stream channels. Water managers are interested in how this impoundment translates to changes in hydrograph dynamics, particularly regarding the magnitude and duration of high flows, the temporary storage of storm water, and the range and spatial distribution of water depths and velocities. High-resolution two-dimensional hydraulic models were developed to compare hydraulic responses to storm events in two 1-kilometer long, relatively small (less than 5-meter-wide channel), urban stream reaches in the Tualatin River Basin (northwestern Oregon) with and without beaver dams. Results from modeling unsteady storm events show that: (1) beaver dams generally attenuate (temporarily impound) more water during storm events than an undammed reach, (2) the timing and dynamics of this attenuation are complicated and thus do not always result in a reduction of peak flows, and (3) the influence of beaver dams on stream hydraulics diminishes as the magnitude of flow events increase. Local geomorphic conditions, specifically the presence of off-channel features, affect the extent to which dams alter hydrograph dynamics. Although the magnitudes of peak flows are not substantially affected by the beaver dams considered in this study, results show that beaver dams temporarily impound a considerable amount of water throughout the duration of storms, which slows water conveyance to downstream reaches. Steady-state streamflow simulations at several streamflow magnitudes were also used to assess how beaver dams affect stream depths, velocities, and inundated areas, which are important factors affecting aquatic habitats. Results show that beaver dams result in a more hydraulically diverse stream, with substantially more inundated area, lower velocities, and greater depths than corresponding undammed scenarios. However, these differences diminish as streamflows increase and the channels overflow their banks and become hydraulically connected to adjacent floodplains. Together, these results confirm that beaver dams can fundamentally change urban stream channel hydraulics, but the influence of these dams is bounded by local geomorphic controls and is diminished at large streamflows.

Suggested Citation

White, J.S., Jones, K.L., and Rounds, S.A., 2025, Effects of beaver dams and ponds on hydrologic and hydraulic responses of storm flows in urban streams of the Tualatin River Basin, northwestern Oregon, chap. B of Jones, K.L., and Smith, C.D., eds., Beavers in the Tualatin River Basin, northwestern Oregon: U.S. Geological Survey Scientific Investigations Report 2025–5039–B, 38 p., https://doi.org/10.3133/sir20255039B.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Preface
  • Acknowledgments
  • Significant Findings
  • Introduction
  • Methods
  • Results
  • Discussion
  • Conclusions and Implications for Management
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Effects of beaver dams and ponds on hydrologic and hydraulic responses of storm flows in urban streams of the Tualatin River Basin, northwestern Oregon
Series title Scientific Investigations Report
Series number 2025-5039
Chapter B
DOI 10.3133/sir20255039B
Publication Date September 30, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Oregon Water Science Center
Description Report: viii, 38 p.; Data Release
Country United States
State Oregon
Other Geospatial Tualatin River Basin
Online Only (Y/N) Y
Additional publication details