Preprint 06-041
SME Annual Meeting Mar. 27-Mar.29, 2006, St. Louis, MO Preprint 06-041 A MEANDER CUTOFF INTO A GRAVEL EXTRACTION POND, CLACKAMAS RIVER, OREGON P. J. Wampler, Grand Valley State Univ., Allendale, MI E. F. Schnitzer, Dept. of Geology and Mineral Industries, Albany, OR D. Cramer, Portland General Electric, Estacada, OR C. Lidstone, Lidstone and Assoc(s)., Fort Collins, CO Abstract Introduction The River Island mining site is located at approximately river mile The River Island site provides a unique opportunity to examine (RM) 15 on the Clackamas River, a large gravel-bed river in northwest the physical changes to a river channel resulting from avulsion into a Oregon. During major flooding in February 1996, rapid channel gravel extraction pond. Data from before and after the meander cutoff change occurred. The natural process of meander cutoff, slowed for allow evaluation of changes to river geometry, sediment transport, several years by dike construction, was accelerated by erosion into temperature, habitat, and channel form. gravel extraction ponds on the inside of a meander bend during the An avulsion is defined as a lateral migration or cutoff of a river. It flood. involves the diversion of water from the primary channel into a new In a matter of hours, the river cut off a meander and began flowing channel that is either created during the event or reoccupied. through a series of gravel pits located on the inside of the meander Avulsions may be rapid or take many years to complete (Slingerland bend. The cutoff resulted in a reduction in reach length of and Smith, 2004).
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