A presentation I gave at River Restoration Northwest\'s Annual Symposium in February 2009. their website: http://rrnw.org/

1. Unconventional Wisdom and the
Effects of Dams on Downstream
Coarse Sediment Supply
3 February 2009
Byron Amerson, Jay Stallman,
John Wooster, and Derek Booth
Sultan River, WA

2. OBJECTIVE
Consider the landscape context of a dam
before drawing conclusions about its
downstream effects.

3. CONCEPTS
THE FLUVIAL SYSTEM
The watershed and river as a mechanism
that routes water and sediment.
Schumm, 1977

4. CONCEPTS
Dams affect downstream flux of sediment
and water.

5. Bed Coarsening
Channel Degradation
Loss of Spawning Gravel
South Fork Feather River

6. CONCEPTS
What About other outcomes?
Need to Consider…
Sediment Supply
Transport Frequency

7. EXCESS
Channel Aggradation
Island and Bar Formation
Vegetation Encroachment
Change in Relative
Sediment Supply
Subtle Effects
Bed Coarsening
Channel Degradation
Habitat Loss
DEFICIT
Change in Relative Transport
LOW HIGH
Frequency
Based on Grant, Schmidt, and Lewis 2003

8. EXCESS
Channel Aggradation
Island and Bar Formation
Vegetation Encroachment
Change in Relative
Sediment Supply
Subtle Effects
CONVENTIONAL
WISDOM
DEFICIT
Change in Relative Transport
LOW HIGH
Frequency
Based on Grant, Schmidt, and Lewis 2003

9. EXCESS
UNCONVENTIONAL
WISDOM
Change in Relative
Sediment Supply
CONVENTIONAL
WISDOM
DEFICIT
Change in Relative Transport
LOW HIGH
Frequency
Based on Grant, Schmidt, and Lewis 2003

10. CONCEPTS
Geology and Geologic History
Topography
Climate and Hydrology
Land Use
Dam Position
Dam Operation

11. Case Studies
 Sultan River, WA
 McKenzie River, OR
 Deschutes River, OR
What are the primary sources of sediment to
the river downstream of the dam?

12. SULTAN RIVER
Washington
WHAT The Jackson
hydroelectric project
operated by
Snohomish PUD
Annual sediment
KEY
mass balance
FINDINGS
remains similar before
and afte damming.
Culmback Dam

13. Sultan River, WA
Culmback
Dam
Spada Lake
Data for this LiDAR DEM was provided by the Snohomish PUD

14. LITHOTOPO UNITS SEDIMENT INPUTS
V-SHAPED VALLEY
• Dominated by debris
flows
• High Sediment Yield

15. LITHOTOPO UNITS SEDIMENT INPUTS
V-SHAPED VALLEY
• Dominated by debris
flows
• High Sediment Yield
TERRACED VALLEY
• Dominated earth
flows
• Moderate Sediment
Yield ROCK FALLS
EARTHFLOWS
GULLIES

16. LITHOTOPO UNITS SEDIMENT INPUTS
V-SHAPED VALLEY
• Dominated by debris
flows
• High Sediment Yield
TERRACED VALLEY
• Dominated earth
flows
• Moderate Sediment
Yield ROCK FALLS
EARTHFLOWS
GULLIES
ALLUVIAL VALLEY
•Sediment input from TRIBUTARIES
upstream
•Low Sediment Yield
BANK FAILURE

17. LITHOTOPO UNITS SEDIMENT INPUTS
V-SHAPED VALLEY
• Dominated by debris
flows
• High Sediment Yield
TERRACED VALLEY
• Dominated earth
flows
• Moderate Sediment
Yield ROCK FALLS
EARTHFLOWS
GULLIES
ALLUVIAL VALLEY
•Sediment input from TRIBUTARIES
upstream
•Low Sediment Yield
BANK FAILURE

18. Sultan River at present-day Spada Lake, 1949.
This reach was a depositional pool-riffle channel.

19. Sultan River at present-day Spada Lake, 1949.
Therefore, the river upstream of
Culmback Dam was a sediment sink, and
contributed relatively little to the
downstream sediment budget.

20. EXCESS
Change in Relative
Sediment Supply
1965 Pre-dam
DEFICIT
Change in Relative Transport
LOW HIGH
Frequency
Based on Grant, Schmidt, and Lewis 2003

21. Sultan River, WA
2003
1965 1983
Active channel
Active channel
175 feet wide
350 feet wide

22. EXCESS
Change in Relative
Sediment Supply
1965 2007
DEFICIT
Change in Relative Transport
LOW HIGH
Frequency
Based on Grant, Schmidt, and Lewis 2003

23. Sultan River, WA
2003
1965 1983
Active channel
Active channel
175 feet wide
350 feet wide

24. McKENZIE RIVER
Oregon
WHAT A Carmen-Smith
hydroelectric project
operated by Eugene
Water and Electric
Board
Sediment mass
KEY
balance Downstream
FINDINGS
of Trailbridge Dam is
similar to reference
conditions.
Trailbridge
Dam

25. McKenzie River, OR
High Cascades Terrane
• Young volcanics
• Low drainage density
• Hydrologically disconnected
• Low Sediment Yield
Western Cascades Terrane
• Older volcanics
• High drainage density
• Hydrologically connected
• High Sediment Yield

26. McKenzie River, OR
Carmen Diversion
Dam
Smith Dam
Trailbridge
Dam

27. McKenzie River, OR
Upper McKenzie
Basin
Smith River
Basin
Deer Creek
Basin
Trailbridge
Dam

28. McKenzie River, OR
Trailbridge
Dam
Deer Creek

29. DESCHUTES RIVER
Oregon
WHAT The Pelton-Round
Butte hydroelectric
project operated jointly
by Portland General
Electric and the
Confederated Warm
Springs Tribes
Subtle response - bed
KEY
texture and spawning
FINDINGS
gravel area are similar
to pre-dam conditions.
Pelton Reregulating Dam

30. Deschutes River, OR
Annual Sediment
Production
Figure From O’Conner et al. 2003

31. Deschutes River, OR
Pelton Round
Butte Project
Annual Sediment
Production
Figure From O’Conner et al. 2003

32. 6000
Mean Monthly Discharge (CFS)
1924-1956
1964-2007
5000
4000
3000
2000
1924 -1956
1964 - 2007
1000
0
May
Mar
Apr
Aug
Jul
Jan
Feb
Jun
Sep
Oct
Dec
Nov
Low Sediment Yield and a Subdued
Hydrograph

33. Recap
 Sultan: Sediment mass balance remains
similar and Channel Adjustment.
 McKenzie: Downstream sediment mass
balance is similar to reference conditions.
 Deschutes: Subtle response, though
reduced sediment supply.

34. CONCLUSION
 Context Matters
 Because as we have seen, landscape
attributes, land use, dam position, and
operation all influence downstream
physical process outcomes.

35. Acknowledgements
THANK YOU
Snohomish PUD
Eugene Water and Electric Board
Portland General Electric and the
Confederated Warm Springs Tribes

36. Our modeling tells us that the modern and
historical mass balance are the same
Modern Sediment Historical Sediment Average Annual
Transport Capacity Transport Capacity Sediment Input
(KT/yr) (KT/yr) (KT/yr)
0.7 - 12 0.2 - 9 ~11
Estimated Modern Mass Estimated Historical
Balance (KT/yr) Mass Balance (KT/yr)
-1 to 10 2 to 10