Extreme river response to climate-induced

aggradation in a forested, montane basin,

Carbon River, Mount Rainier National

Park, Washington, United States

Jonathan Beyeler, Rebecca Rossi, Paul Kennard, Scott Beason

Mount Rainier National Park, Ashford, WA, United States

Carbon River, Mount Rainier National Park, WA, USA

http://www.cr.nps.gov/history/online_books/geology/publications/pp/1547/images/fig1b.jpg

Avulsions unravel the valley floors by inundating floodplains,

undermining trees, mobilizing alluvium, and incising channels.

River avulsions threaten old growth riparian conifer forests.

500–1000 yr-old Douglas fir, cedars,

hemlock, spruce, alders

Avulsions threaten endangered species habitat, the safety

of park visitors, workers, and infrastructure.

WA SR 410, 100-yr flood in 2006 on White R.

Assess the recent

history of the Carbon

River system in

terms of avulsions,

debris flows, erosion.

2006, 2009, and 2011 NAIPs 2012 minus 2008 LiDAR

War of the Woods: questions

1. Is the Carbon River system stable?

1. How is the Carbon River aggradation different than neighboring rivers?

1. Are Carbon River avulsions more frequent than in the last century?

1. What is the role of riparian forests and wood recruitment in these systems?

1. Is the climate-change driven rapid aggradation of the Carbon River system

initiating a shift in landscape form, function, and stability?

Decreases in annual snowpack thickness and longevity lead to

less ice accumulation, terminus retreat, and volumetric thinning.

Thinning and terminus retreat lead to debuttressed moraines,

exposure of steep transport-limited slopes, and debris flows.

questions… answered?

1. Is the Carbon River system stable?

a. it floods with as frequent as a 2yr event

b. Carbon River Rd has such extensive flood damage that repairs are

unrealistic

1. How is the Carbon River aggradation different than neighboring rivers?

2. Are Carbon River avulsions more frequent than in the last century?

3. What is the role of riparian forests and wood recruitment in these systems?

4. Is the climate-change driven rapid aggradation of the Carbon River system

initiating a shift in landscape form, function, and stability?

Debris-flow mobilized material is incorporated into fluvial system,

and channel aggradation is outpacing floodplain development.

~2x-6x steeper!

Main Channel Flood Channel

Overbank flow from perched channels exploits steep lateral

gradients to inundate lower-elevation streamside floodplains.

Sediment and water flow downstream, while avulsion channels

incise into streamside floodplains and migrate headwardly.

Headcuts erode topsoil, undermine tree roots, and incise

new channels by excavating and transporting sediment.

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Road

Mainstem

Cross Sections

Main Channel

Height Above Main Channel

in Meters

-2.9 to -2.5

-2.5 to -2

-2 to -1.5

-1.5 to -1

-1 to -0.5

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3 plus

Height-Above-Water-Surface maps highlight

floodplain/channel disequilibrium, erosional

features, tributary and avulsion channels.

questions… answered?

1. Is the Carbon River system stable?

1. How is the Carbon River aggradation different than neighboring rivers?

a. no lahars since the Little Ice Age to reset valley-bottom base-level

b. data shows aggradation has yet to reach the park boundary

c. where is the sediment going?

1. Are Carbon River avulsions more frequent than in the last century?

2. What is the role of riparian forests and wood recruitment in these systems?

3. Is the climate-change driven rapid aggradation of the Carbon River system

initiating a shift in landscape form, function, and stability?

Avulsions cause tree mortality by breaching floodplain

margins, inundation with debris, and rapid aggradation.

Floods frequently inundate streamside floodplains in the

rainforest, sometimes with as frequent as a 2yr event.

2006 2009

Mainstem avulsions and channel revegetation, within a decade.

2003

Mainstem avulsions and channel revegetation, within a decade.

2006

Mainstem avulsions and channel revegetation, within a decade.

2009

Mainstem avulsions and channel revegetation, within a decade.

2012

Full mainstem avulsion of the Carbon River through floodplain.

2011

Erosion is tied to deposition, shown in 2008-2012 differencing.

questions… answered?

1. Is the Carbon River system stable?

1. How is the Carbon River aggradation different than neighboring rivers?

1. Are Carbon River avulsions more frequent than in the last century?

a. floodplain/channel disequilibrium leads to hysteresis

b. full mainstem avulsions within last decade

c. legacy effect of abandoned road on avulsions, vs avulsions on road

2. What is the role of riparian forests and wood recruitment in these systems?

3. Is the climate-change driven rapid aggradation of the Carbon River system

initiating a shift in landscape form, function, and stability?

Avulsions depend on the proximity of wetted channels to

floodplain margins with steep gradients, during flood events.

2006 2009

Czuba et al. 2012

Old growth floodplains unravel within decades, even a few events.

questions… answered?

1. Is the Carbon River system stable?

1. How is the Carbon River aggradation different than neighboring rivers?

2. Are Carbon River avulsions more frequent than in the last century?

1. What is the role of riparian forests and wood recruitment in these systems?

a. health (alive vs dead)

b. position (standing, fallen, undermined, buried)

c. size (diameter, length, intact rootwad)

2. Is the climate-change driven rapid aggradation of the Carbon River system

initiating a shift in landscape form, function, and stability?

Rapid inundation of streamside floodplains with sediment and

woody debris occurs when avulsions breach floodplain margins.

~1m

Wood is integral for landscape function, but has a complex

role that varies with size, location and position in landscape.

questions… answered?

1. Is the Carbon River system stable?

1. How is the Carbon River aggradation different than neighboring rivers?

1. Are Carbon River avulsions more frequent than in the last century?

2. What is the role of riparian forests and wood recruitment in these systems?

3. Is the climate-change driven rapid aggradation of the Carbon River system

initiating a shift in landscape form, function, and stability?

a. specifically a “tipping point” related to channel width and riparian forest

mortality?

b. many reaches of Carbon River have doubled in width since ~1950s

Take Home Messages

• floodplain/channel battling disequilibrium and hysteresis

• mainstem Carbon River avulsions within last decade

• legacy effect of abandoned road on avulsions, vs

avulsions on road

• wood (live and dead) is integral for landscape function

• role and availability of wood varies with size, location,

and position within landscape

Questions? Thanks!

Thanks to Geological Society of America and Mount Rainier National Park.