HR: 17:00h
AN: H54A-05    [Abstracts]
TI: Controls on the Alluviation of Oxbow Lakes by Bed Load as Observed Along the Sacramento River of California
AU: * Constantine, J A
EM: jconstantine@bren.ucsb.edu
AF: Department of Earth Science, University of California, Santa Barbara, CA 93106, United States
AU: Dunne, T
EM: tdunne@bren.ucsb.edu
AF: Department of Earth Science, University of California, Santa Barbara, CA 93106, United States
AU: Dunne, T
EM: tdunne@bren.ucsb.edu
AF: Donald Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106, United States
AU: Piegay, H
EM: hpiegay@free.fr
AF: Centre National de la Recherche Scientifique, UMR 5600, Lyon, 69362, France
AU: Kondolf, G M
EM: kondolf@calmail.berkeley.edu
AF: Department of Landscape Architecture and Environmental Planning, University of California, Berkeley, CA 94720, United States
AB: As the products of meander cutoff that are widespread within many floodplains, oxbow lakes can affect the ability of rivers to migrate across their valleys, as well as physical and chemical exchanges between the river and floodplain environment. The particular functions of the oxbow lake are determined by the manner it is filled by sedimentation. Although the alluviation of oxbow lakes has been observed in natural settings and generalized by means of rules in planform evolution models, no theory exists to explain how oxbow lakes are filled because the controls on the process have not been widely studied or physically interpreted. Utilizing existing theory and field data from lakes of the Sacramento River, we examined the controls on oxbow alluviation by bed load and found that the transport of bed material through a channel abandoned by cutoff is highly sensitive to the orientation of the abandoned-channel entrance. In particular, the diversion angle, the angle between the approaching active- channel flow and the abandoned-channel entrance, is a direct control on discharge through the abandoned channel, and thus can significantly reduce boundary shear-stress and limit the transport capacity of bed load. The higher the angle, the more greatly reduced is the capacity to transmit bed material, and the more quickly the channel is hydraulically disconnected as diverted bed load rapidly aggrades the channel entrance. In contrast, the lower the angle, the longer the duration the channel remains hydraulically connected, and the more likely it will experience filling and narrowing by bed load because sufficient flow allows for the downstream and transverse transport of bed material. Our findings from the Sacramento River compare well to observations from other large meandering rivers and may explain why some lakes are terrestrialized within decades of cutoff, whereas others remain as open-water habitat for considerably longer.
DE: 1820 Floodplain dynamics
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
DE: 1860 Streamflow
DE: 1861 Sedimentation (4863)
SC: Hydrology [H]
MN: 2007 Fall Meeting