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Alluvial Landscape Response to Climate Change in Glacial Rivers and the Implications to River Restoration
Tim Abbe ENTRIX, Inc. Seattle, WAScott Beason ENTRIX, Inc. Seattle, WAPaul Kennard Mt. Rainier NP, Ashford, WAJim Park WSDOT, Olympia, WA
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PresentationIntroduction
Climate ChangeLandscape SignalsGeomorphic Implications to Rivers
Pacific Northwest Landscape Response to WarmingGlacier Change at Mount RainierEffect on runoff & sediment supplyRiver response to changes
Implications to River RestorationComplications to comeMitigating factors
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IPCC 2007:
The climate is warming.
Sea level is rising.
Glaciers are melting.
Climate Change:
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“Pacific Northwest temperatures are higher than anytime in the last 1300 years”
- Philip Mote, Washington State Climatologist (May, 2007)
“Arctic Sea Ice Extent Plummets in 2007”
- EOS Cover Article (January 8, 2008)
Climate Change:
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Evidence of glacier change (Dyurgerov 2002)
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So how can climate change influence landscape response?
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Boundary Conditions (template for river evolution)• Topography / Relief (potential energy)• Geology / Earth materials (erosion resistance) • Vegetation (erosion resistance)
Drivers for river evolution (Lane’s balance)• Water • Sediment• Debris
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Aggradation: Qc << Qs
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So how can a warming climate change these conditions in glacial
environments?
1) Increase in runoff as more precipitation falls as rain instead of snow resulting in higher sediment transport capacity, Qc.
2) Glacier retreat exposes previously frozen high relief deposits of unconsolidated bare sediments that are easily mobilized. These factors increase sediment supply, Qs.
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>Q2The frequency of peak flows equal or greater than the 2yr flood has doubled in the last 26 yrs compared to the previous 51 yrs.
1) Are increases in peak flows (Qc) occurring?
North Fork Stillaguamish River, WA
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1) Are increases in peak flows (Qc) occurring?
Hoh River, WA
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The frequency of peak flows equal or greater than the 2yr flood has doubled in the last 23 yrs compared to the previous 53 yrs.
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1840 terminus
1905 terminus
1936 terminus
1951 terminus
1956 terminus
1961 terminus1974 terminus
1997 terminus
current terminus
2) Increases in sediment supply (Qs)
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Mount Rainier(West Face)
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Perennial snow and ice on Mount Rainier
• Twenty five named glaciers• 34 square miles• One cubic mile!• Enough to fill Safeco Field in Seattle 2,600 times! • As much perennial snow and ice as on all the
other Cascade volcanoes combined.• Mount Rainier is the largest ice massif in the 48
contiguous states.
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Glacial Changes at Mt. RainierGlacial Changes at Mt. Rainier
• 24 of the 25 glaciers in the park are receding
• All glaciers being monitored are losing mass
• Perennial snowfields are disappearing
So, what does this mean to the rivers?
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Implications of Glacial Recession to RiversImplications of Glacial Recession to Rivers
• Further glacial recession = unstabilized unconsolidated sediment
= prone to failure= debris flows
• There’s literally a “mountain” of debrisSediment coming online is in tens of millions of cubic
meters in some glacial valleys.• Huge sediment supply resulting in “hyper-
aggradation”
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Glaciers leave, sediment comes online…
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Montgomery and Buffington 1997
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Highway 35, Mount Hood, Oregon. November 7, 2006
.. and comes rolling downstream.
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Channel response to increased Channel response to increased Qs and QcQs and Qc
Nisqually River/Van Trump Creek - Lower Van Trump Hairpin - Line 2
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Distance Along Cross Section (Feet, Looking Downstream)
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2005 2006
Debris flow deposition
Mean aggradation of 2 m in one event
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Channel response to increased Channel response to increased Qs and QcQs and Qc
Nisqually River - Longmire - Line 3
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Distance Along Cross Section (Feet, Looking Downstream)
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Fluvial deposition
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Summary of channel aggradation observed in Mt. Rainier Rivers (Beason 2007)
• Historic park-wide rates: <3 in/decade• Van Trump Hairpin: 5.6 feet of aggradation in
one event• Longmire: 6-12 in/decade (2-4x background)• Sunshine Point: 15 in/decade (5x background)• Flood of 2006 recorded more deposition than
erosion despite record peak flows
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Morphologic response associated with channel aggradation:
Recent channel evolution of Tahoma Creek
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Tahoma CreekTahoma Creek1960
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Tahoma CreekTahoma Creek1979
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Tahoma CreekTahoma Creek2006
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AA
Tahoma Creek, Mt. Rainier National Park
BB
CC
Channel Channel aggradationaggradation can get a lot more can get a lot more complicated than complicated than simply raising a river simply raising a river bed. Aggradation bed. Aggradation can lead to noncan lead to non-- intuitive changes intuitive changes ……
2001
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Aggradation doesnAggradation doesn’’t mean channels will always go up!t mean channels will always go up!By 2005 the bed of Tahoma Creek was up to 20 ft higher than surrBy 2005 the bed of Tahoma Creek was up to 20 ft higher than surrounding terrain. This ounding terrain. This aggradationaggradation created conditions for a major avulsion that sent the entire created conditions for a major avulsion that sent the entire mainstemmainstem channel into an unchannel into an un--named tributary drainage along opposite side of the valley.named tributary drainage along opposite side of the valley.
Longitudinal profiles at Tahoma Creek
20052001
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Morphologic response associated with channel aggradation:
Upper White River
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White River: 2005 survey
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Designing Restoration for inherently dynamic systems.
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Draw from the many analogs where natural or human disturbance has altered Qc or Qs, e.g., • Landslide and debris dams• Urbanization• Forest clearing• Flow regulation (dams, diversions)
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Canyon Creek, WAMarch, 2005
Proposal to put in step structures to improve fish passage
So would this approach have worked?
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2004Habitat structures and changing rivers
2008
Aggradation and bed fining of lower Elwha River associated with ELJ placements
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Sediment budget dynamics:Past, present and future
??
?
Current time:Increase in
magnitude and variability of
Qs
Pre-existing:Relatively
stable climate
Vegetation stabilizes
deglaciated terrain
Glaciers at extreme elevations persist in highly variable state
Adjustment to lower Qs than pre-existing
?
Qs
Designing for change & uncertainity
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• Clearly define goals weigh them against realistic assessments of the system and risks.
Choose restoration strategies that accommodate channel response:
• Give the system elements that reduce potential adverse impacts and sustain critical habitat.
• Expect vertical and horizontal changes and design accordingly.
• Delineate geomorphic response corridors.
• Understand the factors controlling landscape evolution, particularly Qc and Qs. Use tools such as UBC Regime Model to evaluate whether an equilibrium condition is possible.
• Build uncertainty into designs and management.
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Geomorphic Response Corridors, Dredging, and Manifest Destiny
Dealing with channel response such as aggradation is already one of the most challenging issues facing river restoration in the PNW – even without climate change.
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LONGMIRE
HIGH
LOW
Nisqually River
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What to do about the sediment?Nisqually River at Longmire, 2004
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Dredge! Nisqually River, Longmire 2006
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2781 ft
2724 ft
57 ft
Dredging Zone
NPI
Homes, Hotel & offices
The future is now at Longmire
Geomorphic Response Corridor
What will it take for us to recognize the inevitable?
Potential habitat:Fish – YesPeople - No
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There are solutions that enhance the environment
and protect people:
1. Space (GRCs)2. Physical elements that mitigate adverse impacts.
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This creek has experienced a change in its flow regime.
What was once its 100 year flood now occurs twice a year.
But unlike many other creeks in this area, it remains in excellent condition, why?
It has lots of wood & accommodates vertical & horizontal complexity
An Intact Geomorphic Response Corridor
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Implications of a warming climate:New flow regimes (Qc)Changing sediment budgets (Qs)Uncertainty
Things to do in restoration and river management:Recognize & delineate “geomorphic response corridors”Design robust structures capable of handling major changes in river:
Vertical & lateral extent of structureEnergy dissipation and sediment storage
Avoid designs assuming “equilibrium” and design to accommodate change & uncertainity
River Restoration in a time of Climate Change