RRNW 2008 [email protected]Alluvial Landscape Response to Climate Change in Glacial Rivers and the Implications to River Restoration Tim Abbe ENTRIX, Inc. Seattle, WA Scott Beason ENTRIX, Inc. Seattle, WA Paul Kennard Mt. Rainier NP, Ashford, WA Jim Park WSDOT, Olympia, WA
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Alluvial Landscape Response to Climate Change in Glacial ...€¦ · climate change. RRNW 2008 [email protected] L i n e 9 L i n e 7 L i n e 6 L i n e 5 L i n e 1 0 L i n e 4 L i n
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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.
• 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
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.
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)
• 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.
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.
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