how debris flow channels refill in the western cascades arianna lambie advisor: frederick swanson...
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How Debris Flow Channels Refill in the Western Cascades
Arianna LambieAdvisor: Frederick Swanson
Ecosystem Informatics Summer Institute
August 2007
My objectives
1) Quantify material volume
• Wood
• Sediment
2) Determine accumulation rates
3) Identify factors influencing accumulation
Data Collected
• Wood– diameter, length, orientation
• Sediment– width, length, depth, composition, obstruction
• Channel in general– Slope, width, other observations
Wood and sediment volumes correlate and increase over time
Relationship Between Wood and Sediment Volume
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0.00 0.20 0.40 0.60 0.80
Volume of w ood per channel length (m3/m)
Vol
ume
of s
edim
ent p
er c
hann
el
leng
th (
m3/
m) 1996
1964
>1964
Approximating Accumulation Rates
Wood Accumulation Over Time
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 100 200 300
Time since last debris f low (years)
Vol
ume
of w
ood
in c
hann
el
(m3/
m) HJ Andrew s
Coast Range
Approximating Accumulation Rates
Sediment Accumulation Over Time
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
0 100 200 300
Time since last debris f low (years)
Vol
ume
of s
edim
ent i
n ch
anne
l (m
3/m
)
HJ Andrew s
Coast Range
Large wood is a primary sediment storage mechanism
Sediment Obstructions
45%
20%
22%
9%
1%2%
2%
.5%
Large Wood
Large and Small Wood
Large Wood and Boulders(and sometimes small wood)
Small Wood
Boulders (>.64m)
Small Wood and Boulders
Hillslump or Bank alone
Shallow Slope alone
The Sediment Story
Sediment
Wood
Hillslump
Remnant debris flow deposits
Material in channel
Root throw, Soil creep, and subsequent transport
Slump earthflow
Previous debris flow
Fluvial transport
Bedrock channel slope
Forest management, Road building
Size, age, health of trees
Debris flow impacts
Debris flow frequency
Solid line = transport
Dashed = influence
Extending the Study
• Fill and rework the influence diagram– Compile data from previous studies– Continue channel data collection, plantations
• Apply math– Fit equations to accumulation rates– Quantify influence pathways
• Investigate biologic impacts– In channel– Downstream
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