The Effects of Beaver Dams on Urban Streams in the Tualatin Basin

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The effects of beaver dams on urban streams in the Tualatin Basin

Erin Poor, Hydrologist

U.S. Department of the Interior U.S. Geological Survey Study Area

10 miles

Streams

Building Footprint

Urban Growth Boundary (2015) Map by USGS Urban Streams

Typical Urban

Hydrograph

Typical Pre-Urban

Hydrograph Stream Flow Stream

Time

Impermeable Surfaces Runoff Incision Suspended Sediment Overarching Question

Can beaver dams be used as a tool to manage stormwater and improve water quality and ecosystem health in an urbanized watershed?

Beaver Dam

Stream Hydraulics Hydraulic Model at Fanno Creek Without Dams With Dams Without Dams With Dams

3.5 ft3/sec 70 ft3/sec

Beaver dams increase wetted area.

Preliminary results; subject to revision Stream Hydraulics Photo courtesy of E.Poor

Beaver dams create diverse aquatic habitat conditions. Storm Simulation Large Storm at Fanno Creek (peak flow ~ 3 Without Beaver Dams With Beaver Dams 210 ft /s)

Preliminary results; subject to revision Hydrograph During Storm Events

Slight decrease Upstream of Beaver Reach Downstream of Beaver

Reach

Stream Flow Stream

Conceptual Graph Time Beaver dams can temporarily store water during storms, causing modest reductions in the magnitude of some storm peaks. Sediment Dynamics Suspended Sediment Concentrations at Fanno Creek 350 Upstream 300 Downstream Replicate 250 Sample pair Samples groupings 200

150

100

Suspended Sediment Concentration (mg/L) Concentration Sediment Suspended 0 0 1 2 3 4 5 6 7 8 9 10 11 Sample Suspended sediment concentrations were generally lower downstream of beaver ponds.

Preliminary results; subject to revision Peak Turbidity During Storms at Fanno Creek

800 PondedUpstream Peak Peak Turbidity Turbidity DownstreamDownstream Peak Peak Turbidity

600 Turbidity

400

200 Peak Turbidity (FNU) Turbidity Peak

0 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

Discrete Discharge Events Peak turbidity was reduced as water traveled through the beaver pond.

Preliminary results; subject to revision 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 Temperature Patterns at Fanno Creek

Water temperatures vary spatially and temporally within the ponded area.

Preliminary results; subject to revision Temperature Patterns at Fanno Creek

7-day running average of the daily maximum temperature 31 29

C ° 23 21

Temperature Temperature 19 17 15 5/25/2017 6/14/2017 7/4/2017 7/24/2017 8/13/2017 9/2/2017

Upstream Shallow, open ponded area 0.37 RM below downstream sensor 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 Sediment Temperature Biodiversity Hydraulics Dynamics Trends Surveys

o Modest peak flow o Store sediment, o Increased spatial o Increased bird reductions reducing peak variation during warm diversity and o Temporarily store turbidity and periods prolonged site use stormwater suspended sediment o Warming in shallow, o New still-water o Increased wetted concentrations open areas, returns to habitat for area, decreased o Accumulated large equilibrium amphibians velocity volumes of sediment temperature o Results courtesy of downstream Clean Water Services

Erin Poor [email protected] 503-251-3240

All photos by E.Poor unless otherwise noted