A Brief Summary of Beaver Mimicry and Streamflow

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Free to Use or Share University of Wyoming 2022 DOI: 10.13140/RG.2.2.33474.91843/1
A Brief Summary of Beaver Mimicry and Streamflow Prepared by Niall Clancy & Marshall Wolf
Background
Beaver restoration and mimicry is growing in
popularity as a means of “low-tech” stream restoration.
a
Beaver restoration is the technique of trapping and
translocating nuisance beavers to areas where dam
building is expected to be beneficial.
b
Beaver mimicry is
the process of building beaver dam analogs (BDAs) to
provide some of the same benefits of real beaver dams.
Both real and analog beaver dams slow water velocities,
capture sediment, increase riparian soil moisture, and
create habitat diversity in streams. These changes are
largely beneficial to stream and riparian vegetation and
organisms, increasing overall riverscape health.
c
However, given that beaver mimicry has only recently
become a widespread restoration technique, there is
question about how beaver dam analogs might impact
downstream water users. We reviewed reports on
streamflow related to beaver mimicry and summarize
their findings here.
Summary of Reports
Because streamflow varies by year, day, and stream
reach, it can be difficult to determine when streamflow
changes are due to natural variation vs. stream
alterations unless changes are large. This is especially
true if groundwater variation is not also monitored.
d
Actively maintained, natural beaver dam complexes are
known to attenuate peak flows and increase late season
flows.
e
While this increased baseflow could be beneficial
to fish and other stream-dwelling organisms, the
magnitude is small enough that meaningful changes to
downstream water rights are unlikely.
f
One study found
beaver colonization of a Utah stream turned a losing
reach (-0.2 ft3/s), into a gaining reach (+1.81 ft3/s and
+2.87 ft3/s in the following 2 yrs).
g
Of 6 studies that quantified streamflow associated with
beaver mimicry (3-14 BDAs ea.), 4 observed minimal or
no difference in discharge.d,
h
,
i
,
j
A study in central Oregon
(21 BDAs) reported a slight decline in streamflow
immediately downstream of BDA’s after initial
construction; the decline lasted for a matter of days and
was followed by a net increase in baseflow relative to
a
See Goldfarb, B. 2018. Eager. Chelsea Green Publishing, Hartford.
b
See beaver.restoration.usu.edu
c
Shahverdian, S.M., et al. 2019. Utah State University Restoration
Consortium. DOI: 10.13140/RG.2.2.14138.03529
d
Bobst, A. 2019. Montana Technological University, guest lecture on 10-
16-2019. digitalcommons.mtech.edu/campus_lectures/95
e
Nyssen, J., et al. 2011. J HYDROL. DOI: 10.1016/j.jhydrol.2011.03.008
f
Hafen, K. 2017. Utah State University, thesis. DOI: 10.26076/657c-5e7c
control locations.
k
This is likely reflective of the time it
takes for ponded water to saturate surrounding soils.
Similarly, a project in western Montana (18 BDAs)
attenuated peak- and low-flows (i.e., stored more water
in spring and released it throughout the late summer).g
Since BDAs are seldom maintained as meticulously as
natural beaver dams, BDAs are more porous and
streamflow impacts are expected to be smaller than those
from natural beaver dams.
Conclusion
• Small BDA projects tend not to have
observable impacts on streamflow.
• Larger BDA projects (~20 BDAs) can store
run-off and increase baseflows.
• Natural variation in streamflow often masks
any potential changes caused by beaver
mimicry projects.
• BDA projects are expected to have little impact
on total downstream water delivery and
potentially positive increases to baseflow.
Niall G. Clancy, MS – PhD student at the University of Wyoming,
Wyoming Cooperative Fish & Wildlife Research Unit
J. Marshall Wolf – PhD candidate at Utah State University,
Department of Watershed Sciences
g
Majerova, M., et al. 2015. HYDRO EARTH SYST SCI. DOI:10.5194/hess-
19-3541-2015
h
Norman, E.G. 2020. Montana Technological University, thesis.
digitalcommons.mtech.edu/grad_rsch/239
i
Munir, T.M. & C.J. Westbrook. 2021. RIVER RES APPLIC. DOI:
10.1002/rra.3753
j
Wolf, J.M. Unpublished data from northern Utah.
k
Weber, N., et al. 2017. EcoLogical Research, report. DOI:
10.13140/RG.2.2.28075.95523
Joe Wheaton (CC-BY)