Alluvial Landscape Response to Climate Change in Glacial ...€¦ · climate change. RRNW 2008...

RRNW 2008 tabbe@entrix.com

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

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

IPCC 2007:

The climate is warming.

Sea level is rising.

Glaciers are melting.

Climate Change:

“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:

Glacier change(Austrian Alps)

Evidence of glacier change (Dyurgerov 2002)

So how can climate change influence landscape response?

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

Lane’s Balance

Channel morphology = f (Qc, Qs)

Montgomery and Buffington 1997

Channel morphology = f (Qc, Qs)

Channel response to increase in peak flows (Qc).

Incision: Qc >> Qs

Aggradation: Qc << Qs

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.

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

>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

1) Are increases in peak flows (Qc) occurring?

Hoh River, WA

-20000

-10000

1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

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.

1840 terminus

1905 terminus

1936 terminus

1951 terminus

1956 terminus

1961 terminus1974 terminus

1997 terminus

current terminus

2) Increases in sediment supply (Qs)

Mount Rainier(West Face)

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.

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?

19742004

Photo: NPS/Scott Beason

Nisqually Glacier

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”

RRNW 2008 tabbe@entrix.comPhoto: NPS

Glaciers leave, sediment comes online…

Montgomery and Buffington 1997

Highway 35, Mount Hood, Oregon. November 7, 2006

.. and comes rolling downstream.

Channel response to increased Channel response to increased Qs and QcQs and Qc

Nisqually River/Van Trump Creek - Lower Van Trump Hairpin - Line 2

0 50 100 150 200 250 300 350 400 450 500 550

Distance Along Cross Section (Feet, Looking Downstream)

2005 2006

Debris flow deposition

Mean aggradation of 2 m in one event

Channel response to increased Channel response to increased Qs and QcQs and Qc

Nisqually River - Longmire - Line 3

0 25 50 75 100 125 150 175

Distance Along Cross Section (Feet, Looking Downstream)

1997 2005 2006

Fluvial deposition

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

Morphologic response associated with channel aggradation:

Recent channel evolution of Tahoma Creek

Tahoma CreekTahoma Creek1960

Tahoma Creek, Mt. Rainier National Park

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 ……

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

Morphologic response associated with channel aggradation:

Upper White River

SR 410

Low or High?

High or Low?

White River: 2005 survey

Forest!!!!

Channel

Tahoma Creek

Photo: Scott Beason

Carbon River Road (preview for SR 410?)

Designing Restoration for inherently dynamic systems.

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)

Canyon Creek, WAMarch, 2005

Proposal to put in step structures to improve fish passage

So would this approach have worked?

Canyon CreekNovember 8, 2006

Well, the money is in the bar.

2004Habitat structures and changing rivers

Aggradation and bed fining of lower Elwha River associated with ELJ placements

Sediment budget dynamics:Past, present and future

Current time:Increase in

magnitude and variability of

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

Designing for change & uncertainity

• 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.

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.

Line 9

Line 7Line 6

Line 5

Line 10

Line 4Line 3

Line 1

Line 2

Line 8Line 8

LONGMIRE

Nisqually River

What to do about the sediment?Nisqually River at Longmire, 2004

Dredge! Nisqually River, Longmire 2006

2781 ft

2724 ft

Dredging Zone

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

There are solutions that enhance the environment

and protect people:

1. Space (GRCs)2. Physical elements that mitigate adverse impacts.

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

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

Alluvial Landscape Response to Climate Change in Glacial ...€¦ · climate change. RRNW 2008...

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