Transcript Marmot Dam Removal Predictions and Observations

2008 AGU Fall Meeting, San Francisco, CA
Marmot Dam Removal
Predictions and Observations
Yantao Cui1, Bruce Orr1, Andrew Wilcox2,
Jen Vick3, Charles Podolak4, and Peter Wilcock4
1.
2.
3.
4.
Stillwater Sciences, 2855 Telegraph Ave., Berkeley, California
Department of Geosciences, U of Montana, Missoula, MT
Consultant, 416 Perry Avenue, Pacifica, CA 94044
Dept. of Geography & Environmental Engineering, Johns
Hopkins University, Baltimore, MD
Courtesy of Portland
General Electric (PGE)
2
50 km to Portland,
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Bull Run
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Little Sandy
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BRIGH TW OOD
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Marmot Diversion
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5 Miles
S till wa te r S ci en c e s. 5 /2 4 /2 00 0
N
Drainage Area:
680 km2 at Marmot Dam
1,120 km2 at Bull Run River confluence
1,305 km2 at Columbia River confluence
3
300
Reach 1
Reach 3
Reach 4
Reach 5
Marmot Dam
200
Reach 0 (reservoir area)
Elevation (m)
250
Reach 2
150
100
50
Revenue Bridge
Dodge Park
Oxbow Park
Dabney Park
0
-5
0
5
10
15
20
25
30
35
40
45
50
Distance from Marmot Dam (km)
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Key Issues Necessitate Sediment
Transport Modeling

Fish habitat
Spawning habitat;
 Rearing habitat;
 Passage.


Piles ~ 600 ft high in a football field!
Home owner –
flooding risks.
5
Modeling Challenges
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Coupled modeling of up- and downstream
reaches;
Large size range (0.5 – 250 mm);
Stratified sediment deposit;
Large temporal scale (~ 10 years);
Large spatial scale (~50 km).
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Model Foundation

Sediment pulse work (Gary Parker, Tom Lisle, Jim
Pizzuto, Yantao Cui and colleagues);

Reservoir deposit = sediment pulse,
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Sediment pulse model should work for dam
removal simulation with some adaptations.
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Simulated Dam Removal Alternatives
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Blow-and-go;
Two season staged removal;
Dredging prior to dam removal.
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Results of Sediment Transport
Modeling
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
Staged two-season removal provides absolutely no
benefit;
Dredging 15% of sediment (the max can be
dredged in one year) provides minimal benefit in
terms of minimizing downstream sediment
deposition;
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Selection of Dam Removal Option

Because multiple-year dredging is technically
unreliable (a winter storm may completely fill in
the previous dredging slot) and economically
unacceptable, the only sensible dam removal
alternative is blow-and-go, provided that
modeling results indicated no serious impacts.
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Key Results
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
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
Reservoir erosion
starts fast but
slowdown after
year one;
Not depositing
everywhere;
Need a few years.
Reach 2
Reach 1
Reach 0
Modeling
Results
Vertical Scale:
each grid = 1 m
Reach 3
Horizontal Scale:
10 km
Reach 4
Reach 5
Initial
1st year
2nd year
3rd year
4th year
5th year
6th year
7th year
8th year
9th year
10th year
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Modeling
Results
Vertical Scale:
each grid = 0.3 m/yr
Horizontal Scale:
10 km
Reach 1
Reach 2
Reach 3
Reach 4
Reach 5
1st year
2nd year

Annual change is
small except
during the first
couple of years at
selected
locations.
3rd year
4th year
5th year
6th year
7th year
8th year
9th year
10th year
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Modeling Results

Sand pass through the river quickly to the Columbia River;
Sand deposition is minor and near mouth.
1.2
1
Thickness of Sand Deposition (m)

0.8
0.6
0.4
0.2
0
34
36
38
40
42
Distance from Marmot Dam (km)
44
46
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Modeling Results
DTSS < 500 ppm;
 Spikes associated with storm events;
 Fish ok!

Suspended Sediment Concentration (ppm)
1000
Marmot Dam (0 km)
Sandy below Bull Run River confluence (20 km)
Downstream of Dabney Park (40 km)
100
10
0
365
Time (days)
730
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Monitoring
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
Reach 2
Reach 1
Reach 4
Repeat Surveys
Deposit Volume
 Deposit Location
Reach 5
Initial
1st year
Summer 2007Summer 2010


Reach 3
Horizontal Scale:
10 km
4 years


Reach 0
NCED Field
Measurements
Vertical Scale:
each grid = 1 m
2nd year
3rd year
Chuck’s play ground!
4th year
5th year
PGE survey
LiDAR
survey
forinend
2006,
point
2007
analysis!
and 2008.6th year
Pebble counts
7th year
Surface GSD
8th year

9th year
10th year
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Comparisons with Observations One
Year After Removal
The quick initial erosion of the reservoir
deposit without forming a head-cut;
Low TSS except in the first few hours (Major
et al. 2008 EOS Transactions);
Deposition in Reach 1, almost nothing further
downstream.
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Reservoir Area
Change in Average Bed Elevation
One Year Following Dam Removal (m)
2
0
Dry
-2
Wet
Average
-4
Note: modeling results (lines) used discharge
record of a wet, an average, and a dry year as
model input, providing three different
predictions.
-6
-8
Flow direction
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2.5
2
1.5
1
0.5
0
Distance Upstream from Marmot Dam (km)
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5
5
Average
3
4
2
1
3
Dry
Average year
Wet year
Dry year
results (lines) used discharge
0 Note: modeling
Wet
record of a wet, an average, and a dry year as
-1 model input, providing three different
predictions.
0
0.3
0.6
0.9
1.2
2
1.5
1.8
1
0
-1
0
Reach 2
Reach 3
Reach 1
Change in Average Bed Elevation
One Year Following Dam Removal (m)
PGE survey data
4
10
Reach 4
20
30
Distance from Marmot Dam (km)
Reach 5
40
20
NCED Field Measurements (C. Podolak)
Vertical Scale:
each grid = 1 m
Reach 2

Reach 1

Wedge in upper part of reach 1
No measurable deposition in study areas in reaches 2, 3
or 4
No measurable change in GSD in downstream reaches
m 0tall)
Marmot Dam (14.7
Reach

Reach 3
Horizontal Scale:
10 km
Reach 4
Reach 5
Initial
(Note: simulation results are based on average hydrologic condition.)
1st year
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Perspective
Not much change beyond this reach. Primary concern here was fish
passage.
Primary spawning habitat. The deposit was allowed to go
downstream because modeling results indicated not much will
occur here. All the signs to date show that modeling results
will remain true in the future, but we may want to wait for a few
years before we can give the prediction a final verdict.
250
Elevation (m)
200
150
100
50
0
-5
0
5
10
15
20
25
30
Distance from Marmot Dam (km)
35
40
45
50
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Jul 5, 2007 587 cfs
Nov 14, 2008 2800 cfs
Jan 26, 2008 850 cfs
Nov 17, 2008 1150 cfs
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Final Remarks
Chapter 23
Sedimentation Engineering, ASCE Manual
110, M.H. Garcia Ed.
www.stillwatersci.com
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Acknowledgement
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Funding from Portland General Electric (PGE);
Helpful discussions with Tom Lisle and Bill
Dietrich during modeling;
Support and help from PGE and Stillwater
Sciences staff;
Review of modeling report by Bill Dietrich,
Marcelo Garcia, Tom Lisle, Jim Pizzuto, and
Steve Wiele.
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