Geologic Publications for Mount Rainier

Geomorphic response to significant sediment loading in Tahoma Creek, Mt. Rainier, WA

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Author(s): Scott W. Anderson, Paul M. Kennard, John Pitlick

Category: POSTER
Document Type: Abstract #EP53C-1055
Publisher: American Geophysical Union, Fall Meeting 2012
Published Year: 2012
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Abstract:
Increased sediment loading in streams draining the flanks of Mt. Rainier has caused significant damage to National Park Service infrastructure and has prompted concern in downstream communities. The processes driving sedimentation and the controls on downstream response are explored in the 37 km² Tahoma Creek basin, using repeat LiDAR surveys supplemented with additional topographic datasets. DEM differencing between 2003 and 2008 LiDAR datasets shows that over 2.2 million cubic meters of material was evacuated from the upper reaches of the basin, predominately in the form of debris flows. These debris flows were sourced in recently exposed lateral moraines, bulking through the broad collapse of unstable hillslopes. 40% of this material was deposited in the historic debris fan 4-6 km downstream of the terminus, while 55% completely exited the system at the downstream point of the surveys. Distinct zones of aggradation and incision of up to one meter are present along the lower channel and appear to be controlled by valley constrictions and inflections. However, the lower channel has shown remarkable long-term stability in the face of significant sediment loads. Alder ages suggest fluvial high stands in the late 70's and early 90's, immediately following periods of significant debris flow activity, yet the river quickly returned to pre-disturbance elevations. On longer time scales, the presence of old-growth forest on adjacent floodplain/terrace surfaces indicates broad stability on both vertical and horizontal planes. More than a passive indicator, these forested surfaces play a significant role in maintaining channel stability through increased overbank roughness and the formation of bank-armoring log jams. Sediment transport mechanics along this lower reach are explored using the TomSED sediment transport model, driven by data from an extensive sediment sampling and stream gaging effort. In its current state, the model is able to replicate the stability of the channel but significantly under predicts total loads when compared to the LiDAR differencing.

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In Text Citation:
Anderson and others (2012) or (Anderson et al., 2012)

References Citation:
Anderson, S.W., P.M. Kennard, and J. Pitlick, 2012, Geomorphic response to significant sediment loading in Tahoma Creek, Mt. Rainier, WA: Abstract #EP53C-1055, American Geophysical Union, Fall Meeting 2012,