1. Overview of the Tualatin Urban Beaver Dam Study

Populations of North American beaver (Castor canadensis) have increased in recent years due to decreased trapping, habitat restoration, and recognition of their importance as a keystone species in stream ecosystems (Pollock and others, 2017). Previous studies have shown that beaver dams and associated ponds can change channel morphology, trap sediment (and attached pollutants), alter the composition and amount of riparian vegetation, slow down and push water into the floodplain, and change surrounding habitats for fish, amphibians, and birds in rural and mountainous streams. Little work, however, has been done to quantify the effects of beaver dams and ponds on urban streams.

The U.S. Geological Survey (USGS), in collaboration with Clean Water Services, is working to fill this knowledge gap and provide usable information for water-resource managers, regulators, and restoration practitioners. This study focuses on urban streams in the Tualatin River basin, where flashy hydrographs and channel incision have resulted in simplified stream habitats. As Clean Water Services and others consider restoration strategies that include encouraging beaver dam building or adding beaver dam analogs (BDAs) in urban streams, understanding the multi-faceted benefits and impacts of beaver dams and ponds is important context for anticipating and communicating realistic types and associated magnitudes of changes related to beaver dams, ponds, and habitat trajectories.