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

epoor@usgs.gov

503-251-3240

All photos by E.Poor unless otherwise noted

Erin Poor