Geologic Publications for Mount Rainier

River bed elevation changes and increasing flood hazards in the Nisqually River at Mount Rainier National Park, Washington

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Author(s): Sharain O. Halmon, Paul M. Kennard, Scott R. Beason, Elizabeth Beaulieu, Lloyd W. Mitchell

Category: PRESENTATION
Document Type: Abstract #H11B-1256
Publisher: American Geophysical Union, Fall Meeting 2006
Published Year: 2006
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Abstract:
Mount Rainier, located in Southwestern Washington, is the most heavily glaciated volcano of the Cascade Mountain Range. Due to the large quantities of glaciers, Mount Rainier also has a large number of braided rivers, which are formed by a heavy sediment load being released from the glaciers. As sediment builds in the river, its bed increases, or aggrades,its floodplain changes. Some contributions to a river's increased sediment load are debris flows, erosion, and runoff, which tend to carry trees, boulders, and sediment downstream. Over a period of time, the increased sediment load will result in the river's rise in elevation. The purpose of this study is to monitor aggradation rates, which is an increase in height of the river bed, in one of Mount Rainier's major rivers, the Nisqually. The studied location is near employee offices and visitor attractions in Longmire. The results of this study will also provide support to decision makers regarding geological hazard reduction in the area. The Nisqually glacier is located on the southern side of the volcano, which receives a lot of sunlight, thus releasing large amounts of snowmelt and sediment in the summer. Historical data indicate that several current features which may contribute to future flooding, such as the unnatural uphill slope to the river, which is due to a major depositional event in the late 1700s where 15 ft of material was deposited in this area. Other current features are the glaciers surrounding the Nisqually glacier, such as the Van Trump and Kaultz glaciers that produced large outbursts, affecting the Nisqually River and the Longmire area in 2001, 2003, and 2005. In an effort to further explore these areas, the research team used a surveying device, total station, in the Nisqually River to measure elevation change and angles of various positions within ten cross sections along the Longmire area. This data was then put into GIS for analyzation of its current sediment level and for comparison to previous cross sections, which were in 1993 and 2005. Results of the data analysis revealed changes in altitude of the sediment, as well as new areas of built up sediment. For example, a 7 foot increase in elevation, which was not revealed in the 2005 data, indicated there was an increased amount of debris that traveled from upstream. Further data will be obtained once all the cross sections are completed and data is closer analyzed.

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Suggested Citations:
In Text Citation:
Halmon and others (2006) or (Halmon et al., 2006)

References Citation:
Halmon, S.O., P.M. Kennard, S.R. Beason, E. Beaulieu, and L.W. Mitchell, 2006, River bed elevation changes and increasing flood hazards in the Nisqually River at Mount Rainier National Park, Washington: Abstract #H11B-1256, American Geophysical Union, Fall Meeting 2006,