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A presentation I gave at River Restoration Northwest\'s Annual Symposium in February 2009.their website: http://rrnw.org/
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Unconventional Wisdom and the Effects of Dams on Downstream Coarse Sediment Supply
3 February 2009
Sultan River, WA
Byron Amerson, Jay Stallman,
John Wooster, and Derek Booth
OBJECTIVE
Consider the landscape context of a dam
before drawing conclusions about its
downstream effects.
CONCEPTS
THE FLUVIAL SYSTEM
The watershed and river as a mechanism
that routes water and sediment.
Schumm, 1977
CONCEPTS
Dams affect downstream flux of sediment
and water.
Bed Coarsening
Channel Degradation
Loss of Spawning Gravel
South Fork Feather River
CONCEPTS
What About other outcomes?
Need to Consider…
Sediment Supply
Transport Frequency
EXCESS
DEFICIT
HIGHLOW
Ch
an
ge i
n R
ela
tive
Sed
imen
t S
up
ply
Bed Coarsening
Channel Degradation
Habitat Loss
Subtle Effects
Channel Aggradation
Island and Bar Formation
Vegetation Encroachment
Change in Relative Transport
FrequencyBased on Grant, Schmidt, and Lewis 2003
EXCESS
DEFICIT
HIGHLOW
CONVENTIONAL
WISDOM
Ch
an
ge i
n R
ela
tive
Sed
imen
t S
up
ply
Change in Relative Transport
FrequencyBased on Grant, Schmidt, and Lewis 2003
Subtle Effects
Channel Aggradation
Island and Bar Formation
Vegetation Encroachment
EXCESS
DEFICIT
HIGHLOW
CONVENTIONAL
WISDOM
Ch
an
ge i
n R
ela
tive
Sed
imen
t S
up
ply
Change in Relative Transport
FrequencyBased on Grant, Schmidt, and Lewis 2003
UNCONVENTIONAL
WISDOM
CONCEPTS
Geology and Geologic History
Topography
Climate and Hydrology
Land Use
Dam Position
Dam Operation
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?
SULTAN RIVER
The Jackson hydroelectric project operated by Snohomish PUD
Washington
Annual sediment mass balance remains similar before and afte damming.
WHAT
KEY FINDINGS
Culmback Dam
Sultan River, WA
Spada Lake
Culmback
Dam
Data for this LiDAR DEM was provided by the Snohomish PUD
LITHOTOPO UNITS SEDIMENT INPUTS
• Dominated by debris
flows
• High Sediment Yield
V-SHAPED VALLEY
LITHOTOPO UNITS SEDIMENT INPUTS
V-SHAPED VALLEY
EARTHFLOWS
GULLIES
ROCK FALLS
TERRACED VALLEY
• Dominated earth
flows
• Moderate Sediment
Yield
• Dominated by debris
flows
• High Sediment Yield
LITHOTOPO UNITS SEDIMENT INPUTS
• Dominated by debris
flows
• High Sediment Yield
EARTHFLOWS
GULLIES
ROCK FALLS
• Dominated earth
flows
• Moderate Sediment
Yield
TRIBUTARIES
ALLUVIAL VALLEY
BANK FAILURE
V-SHAPED VALLEY
TERRACED VALLEY
•Sediment input from
upstream
•Low Sediment Yield
LITHOTOPO UNITS SEDIMENT INPUTS
• Dominated by debris
flows
• High Sediment Yield
EARTHFLOWS
GULLIES
ROCK FALLS
• Dominated earth
flows
• Moderate Sediment
Yield
TRIBUTARIES•Sediment input from
upstream
•Low Sediment YieldBANK FAILURE
ALLUVIAL VALLEY
V-SHAPED VALLEY
TERRACED VALLEY
Sultan River at present-day Spada Lake, 1949.
This reach was a depositional pool-riffle channel.
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.
EXCESS
DEFICIT
HIGHLOW
Ch
an
ge i
n R
ela
tive
Sed
imen
t S
up
ply
Change in Relative Transport
FrequencyBased on Grant, Schmidt, and Lewis 2003
1965 Pre-dam
Sultan River, WA
Active channel
350 feet wide
Active channel
175 feet wide
1965 1983 2003
EXCESS
DEFICIT
HIGHLOW
Ch
an
ge i
n R
ela
tive
Sed
imen
t S
up
ply
Change in Relative Transport
FrequencyBased on Grant, Schmidt, and Lewis 2003
1965 2007
Sultan River, WA
Active channel
350 feet wide
Active channel
175 feet wide
1965 1983 2003
McKENZIE RIVER
A Carmen-Smith hydroelectric project operated by Eugene Water and Electric Board
Oregon
Sediment mass balance Downstream of Trailbridge Dam is similar to reference conditions.
WHAT
KEY FINDINGS
Trailbridge
Dam
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
McKenzie River, OR
Carmen Diversion
Dam
Smith Dam
Trailbridge
Dam
McKenzie River, OR
Upper McKenzie
Basin
Smith River
Basin
Deer Creek
Basin
Trailbridge
Dam
McKenzie River, OR
Deer Creek
Trailbridge
Dam
DESCHUTES RIVER
The Pelton-Round Butte hydroelectric project operated jointly by Portland General Electric and the Confederated Warm Springs Tribes
Oregon
Subtle response - bed texture and spawning gravel area are similar to pre-dam conditions.
WHAT
KEY FINDINGS
Pelton Reregulating Dam
Deschutes River, OR
Annual Sediment
Production
Figure From O’Conner et al. 2003
Deschutes River, OR
Annual Sediment
Production
Figure From O’Conner et al. 2003
Pelton Round
Butte Project
0
1000
2000
3000
4000
5000
6000
Oct
No
v
Dec
Jan
Feb
Mar
Ap
r
May
Ju
n
Ju
l
Au
g
Sep
1924-1956
1964-2007
Mean
Mo
nth
ly D
isch
arg
e (
CF
S)
Low Sediment Yield and a Subdued
Hydrograph
1924 -1956
1964 - 2007
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.
CONCLUSION
Context Matters
Because as we have seen, landscape
attributes, land use, dam position, and
operation all influence downstream
physical process outcomes.
Acknowledgements
Snohomish PUD
Eugene Water and Electric Board
Portland General Electric and the
Confederated Warm Springs Tribes
THANK YOU
Our modeling tells us that the modern and
historical mass balance are the same
Modern Sediment
Transport Capacity
(KT/yr)
Historical Sediment
Transport Capacity
(KT/yr)
Average Annual
Sediment Input
(KT/yr)
0.7 - 12 0.2 - 9 ~11
Estimated Modern Mass
Balance (KT/yr)
Estimated Historical
Mass Balance (KT/yr)
-1 to 10 2 to 10