Hydraulic sedimentary processes causing anastomosing morphology of the upper Columbia River, British Columbia, Canada

B. Makaske, D.G. Smith, H.J.A. Berendsen, A. de Boer, M.F. van Nielen-Kiezebrink, T. Locking

Research output: Chapter in Book/Report/Conference proceedingAbstract

Abstract

The upper Columbia River, British Columbia, Canada, shows typical anastomosing morphology — multiple interconnected channels that enclose floodbasins — and lateral channel stability. We analysed field data on hydraulic and sedimentary processes and show that the anastomosing morphology of the upper Columbia River is caused by sediment (bedload) transport inefficiency, in combination with very limited potential for lateral bank erosion because of very low specific stream power (= 2.3 W/m2) and cohesive silty banks. In a diagram of channel type in relation to flow energy and median grain size of the bed material, data points for the straight upper Columbia River channels cluster separately from the data points for braided and meandering channels. Measurements and calculations indicate that bedload transport in the anastomosing reach of the upper Columbia River decreases downstream. Because of lateral channel stability no lateral storage capacity for bedload is created. Therefore, the surplus of bedload leads to channel bed aggradation, which outpaces levee accretion and causes avulsions because of loss of channel flow capacity. This avulsion mechanism applies only to the main channel of the system, which transports 87% of the water and > 90% of the sediment in the cross-valley transect studied. Because of very low sediment transport capacity, the morphological evolution of most secondary channels is slow. Measurements and calculations indicate that much more bedload is sequestered in the relatively steep upper anastomosing reach of the upper Columbia River than in the relatively gentle lower anastomosing reach. With anastomosing morphology and related processes (e.g., crevassing) being best developed in the upper reach, this confirms the notion of upstream rather than downstream control of upper Columbia River anastomosis.
Original languageEnglish
Title of host publication27 th IAS Meeting of sedementology, Sedimentary environments of Mediteranean Island(s), Alghero, Italy, 20 - 23 September, 2009
EditorsV. Pascucci, S. Andreucci
Place of PublicationAlghero, Italy
PublisherEDES
Pages259-259
ISBN (Print)9788860251237
Publication statusPublished - 2009
Event27 th IAS Meeting of sedementology, Sedimentary environments of Mediteranean Island(s, Alghero, Italy -
Duration: 20 Sep 200923 Sep 2009

Conference

Conference27 th IAS Meeting of sedementology, Sedimentary environments of Mediteranean Island(s, Alghero, Italy
Period20/09/0923/09/09

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