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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
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OBJECTIVE
Consider the landscape context of a dam
before drawing conclusions about its
downstream effects.
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CONCEPTS
THE FLUVIAL SYSTEM
The watershed and river as a mechanism
that routes water and sediment.
Schumm, 1977
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CONCEPTS
Dams affect downstream flux of sediment
and water.
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Bed Coarsening
Channel Degradation
Loss of Spawning Gravel
South Fork Feather River
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CONCEPTS
What About other outcomes?
Need to Consider…
Sediment Supply
Transport Frequency
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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
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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
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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
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CONCEPTS
Geology and Geologic History
Topography
Climate and Hydrology
Land Use
Dam Position
Dam Operation
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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?
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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
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Sultan River, WA
Spada Lake
Culmback
Dam
Data for this LiDAR DEM was provided by the Snohomish PUD
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LITHOTOPO UNITS SEDIMENT INPUTS
• Dominated by debris
flows
• High Sediment Yield
V-SHAPED VALLEY
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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
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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
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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
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Sultan River at present-day Spada Lake, 1949.
This reach was a depositional pool-riffle channel.
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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.
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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
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Sultan River, WA
Active channel
350 feet wide
Active channel
175 feet wide
1965 1983 2003
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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
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Sultan River, WA
Active channel
350 feet wide
Active channel
175 feet wide
1965 1983 2003
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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
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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
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McKenzie River, OR
Carmen Diversion
Dam
Smith Dam
Trailbridge
Dam
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McKenzie River, OR
Upper McKenzie
Basin
Smith River
Basin
Deer Creek
Basin
Trailbridge
Dam
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McKenzie River, OR
Deer Creek
Trailbridge
Dam
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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
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Deschutes River, OR
Annual Sediment
Production
Figure From O’Conner et al. 2003
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Deschutes River, OR
Annual Sediment
Production
Figure From O’Conner et al. 2003
Pelton Round
Butte Project
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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
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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.
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CONCLUSION
Context Matters
Because as we have seen, landscape
attributes, land use, dam position, and
operation all influence downstream
physical process outcomes.
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Acknowledgements
Snohomish PUD
Eugene Water and Electric Board
Portland General Electric and the
Confederated Warm Springs Tribes
THANK YOU
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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