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U.S. Department of the Interior U.S. Geological Survey
The effects of beaver dams on urban
streams in the Tualatin Basin
Erin Poor, Hydrologist
Study Area
Map by USGS
Streams
Building Footprint
Urban Growth Boundary (2015)
10 miles
Time
Str
eam
Flo
w
Typical Urban
Hydrograph
Typical Pre-Urban
Hydrograph
Urban Streams
Impermeable Surfaces Runoff Incision Suspended Sediment
Beaver Dam
Overarching Question
Can beaver dams be used as a tool to manage
stormwater and improve water quality and
ecosystem health in an urbanized watershed?
Stream Hydraulics
Without Dams
3.5 ft3/sec 70 ft3/sec
Preliminary results; subject to revision
Hydraulic Model
With Dams Without Dams With Dams
at Fanno Creek
Beaver dams increase wetted area.
Stream Hydraulics
Beaver dams create diverse aquatic habitat conditions.
Photo courtesy of E.Poor
Preliminary results; subject to revision
Without Beaver Dams With Beaver Dams
Large Storm
(peak flow ~
210 ft3/s)
Storm Simulation at Fanno Creek
Hydrograph During Storm Events
Slight
decrease Upstream of Beaver Reach
Str
eam
Flo
w
Time
Downstream of Beaver
Reach
Beaver dams can temporarily store water during storms, causing modest reductions in the magnitude of some storm peaks.
Conceptual Graph
Sediment Dynamics
Upstream
Downstream
Sample pair
groupings
0
50
100
150
200
250
300
350
0 1 2 3 4 5 6 7 8 9 10 11
Su
spen
ded
Sed
imen
t C
on
cen
trati
on
(m
g/L
)
Sample
Replicate
Samples
Suspended Sediment Concentrations
Preliminary results; subject to revision
Suspended sediment concentrations were generally lower downstream of beaver ponds.
at Fanno Creek
0
200
400
600
800
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Peak T
urb
idit
y (
FN
U)
Discrete Discharge Events
Ponded Peak Turbidity
Downstream Peak Turbidity
Peak Turbidity During Storms
Preliminary results; subject to revision
Upstream Peak Turbidity
Downstream Peak
Turbidity
Peak turbidity was reduced as water traveled through the beaver pond.
at Fanno Creek
Sediment Storage
More than 1,200 m3 of fine sediment has been deposited in the large beaver pond.
Preliminary results; subject to revision
Temperature Patterns
Preliminary results; subject to revision
Temperature Patterns
at Fanno Creek
Water temperatures vary spatially and temporally within the ponded area.
Temperature Patterns
15
17
19
21
23
25
27
29
31
5/25/2017 6/14/2017 7/4/2017 7/24/2017 8/13/2017 9/2/2017
Tem
pera
ture
°C
7-day running average of the daily maximum temperature
Upstream Shallow, open ponded area 0.37 RM below downstream sensor
at Fanno Creek
Water temperature increases in shallow pond, but is cooler 0.4 miles downstream of the beaver reach where the channel is confined and shaded.
Preliminary results; subject to revision
Biodiversity
Birds in Beaver Habitats
Since beaver built dams, more species of birds are using Greenway Park for longer periods.
Results courtesy of Clean Water Services
Amphibians in Fanno Creek
Beaver dams and ponds create new still-water habitat that amphibians are using for breeding and egg-laying.
Results courtesy of Clean Water Services
Summary
Stream
Hydraulics
Sediment
Dynamics
Temperature
Trends
Biodiversity
Surveys
o Modest peak flow
reductions
o Temporarily store
stormwater
o Increased wetted
area, decreased
velocity
o Increased spatial
variation during warm
periods
o Warming in shallow,
open areas, returns to
equilibrium
temperature
downstream
o Increased bird
diversity and
prolonged site use
o New still-water
habitat for
amphibians o Results courtesy of
Clean Water Services
o Store sediment,
reducing peak
turbidity and
suspended sediment
concentrations
o Accumulated large
volumes of sediment