Tuesday, May 5, 2009
Rivers gone wild – Alluvial landscape response to climate change in Mount Rainier
The magnitude and rate at which landscapes respond to climate change is a critical question for National Park management, and the downstream communities. Climate-induced changes to stream flow, sediment, and large wood regimes further compound landuse and development-related geomorphic response.
Geomorphic evidence of the response of glacial systems to the warming climate is found in the rivers draining Mount Rainier. Ongoing glacial recession has exposed large volumes of unconsolidated and oversteepened sediment, and altered hydrologic regimes. These new sources of sediment promote highly erosive debris flows, with widespread geographic distribution. Additionally, climate change is expected to increase storminess, and therefore the frequency of debris flows and flooding. Stream flow records at Mount Rainier show a striking increase in the occurrence of large floods.
Normal fluvial processes, and episodic floods and debris flows, are dramatically increasing sediment supply to downstream rivers. These processes are accelerating channel aggradation, and diminishing stream channel conveyance capacities, and severely aggravating flooding.
Channel surveys taken before and after extreme flooding in November 2006 indicate that even this record-setting event did not provide sufficient sediment transport to offset inputs. During 36 hours of flooding, channels vertically aggraded to a degree that would have normally taken 20 years, at the historic aggradation rate. Damage to infrastructure, and the resulting 6-month park closure, was unprecedented in 108-year history of the Park.
River aggradation is altering entire valley bottoms, burying old growth riparian forests and overwhelming infrastructure, constructed under different design conditions. In one location, the bed of the White River is 5 m above State Route 410, a major state highway situated along the valley margin.
The changing landscape within Mount Rainier National Park is a siren call to downstream communities, and other alpine glacier-sourced watersheds. For example, emergency response and highway protection measures by the Washington Department of Transportation, related to channel aggradation and migration, are costing millions of dollars. An understanding of geomorphic responses to climate change is indispensable when evaluating risks of infrastructure near rivers.
Beason, S.R. and P.M. Kennard, 2006, "Environmental and ecological implications of aggradation in braided rivers at Mount Rainier National Park", NPS Natural Resource Year in Review-2006.
Paul Kennard has been an earth scientist for over 25 years, and specializes in hillslope and fluvial geomorphology, and river restoration. Currently he is Regional Geomorphologist, stationed at Mount Rainier National Park, where he provides technical analyses of (1) river flooding and debris flow hazards; (2) erosion and landslide potential; (3) river channel movement and stream bank erosion; (4) glacier influences; and (5) riparian and in-stream large wood interactions. Previously, he was Senior Staff Scientist at the Washington Forest Law Center (a public service non-profit organization), assessing forested watersheds and forest aquatic resources. Before that, he was a Geomorphologist for 11 years for the Tulalip Indian Tribes of Washington State, where he evaluated the effects of forest activities on fish habitat in the Tulalip Tribes Treaty Areas in western Washington.
Paul Kennard's recent and on-going scientific research includes the effect of climate change at Mount Rainier on: (1) glacier response; (2) river filling and proliferating flooding hazards; and (3) increased debris flows and the effect on park infrastructure.