RETURN TO THE FLOODPLAIN: THE ROLE OF BEAVERS (CASTOR CANADENSIS) IN RESTORING CHANNEL COMPLEXITY AT WASSON CREEK
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Date
2004-08
Authors
Marshall, Sarah Marie
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Beavers (Castor canadensis) are a keystone species capable ofrapidly altering
habitat and hydrologic conditions in aquatic ecosystems. At Wasson Creek, a degraded
stream in the South Slough National Estuarine Research Reserve, beaver activity may be
able to restore channel complexity. To evaluate current conditions and the influence of
beavers at Wasson Creek, I recorded stream stage in high and low beaver activity areas
relative to a range of precipitation events, measured stream channel patterns and the fate
of over-bank flow on the floodplain, mapped change in the original agricultural ditch
through time, and monitored beaver activity.
During the study, Wasson Creek over-topped the banks of the main channel at the
two stage- recording sites in response to a 6-10-year storm event. Following the event,
the floodplain above the two largest beaver dams and around dams in a shallower,
narrower secondary channel remained inundated for most of the study period. Despite
minimal change in the path and sinuosity of the main channel over 65 years, beaver
activity has altered water movt:ment on the floodplain-particularly in areas where
beaver dams cross the floodplain, beavers excavated channels on the floodplain, and
flows were re-directed into a smaller, secondary drainage ditch. Given the high level of
beaver activity on the floodplain (17 actively maintained dams) and suitable habitat, we
can expect beavers to remain in the system- further creating a new complex of channels
and wetlands on the Wasson Creek floodplain. Human intervention may be necessary to
control reed canary grass (Phalaris arundinacea) and other invasive species.
Description
101 pages. A thesis presented to the Department of Environmental Science and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2004.