HR: 0800h
AN: H51E-0821    [Abstracts]
TI: Legacy Sediments and Channel Morphology in the Feather and Yuba Rivers, California
AU: * James, A
EM: AJames@sc.edu
AF: University of South Carolina, Geography Department 709 Bull Street, Columbia, SC 29208, United States
AU: Ghoshal, S
EM: SubhajitGhoshal@gmail.com
AF: University of South Carolina, Geography Department 709 Bull Street, Columbia, SC 29208, United States
AU: Megison, M E
EM: mmegis1@yahoo.com
AF: University of South Carolina, Geography Department 709 Bull Street, Columbia, SC 29208, United States
AU: Singer, M B
EM: bliss@bren.ucsb.edu
AF: University of California, Institute for Computational Earth Systems Science, Santa Barbara, CA 93106, United States
AU: Aalto, R
EM: Rolf.Aalto@exeter.ac.uk
AF: University of Exeter, Department of Geography, Exeter, EX4 4RJ, United Kingdom
AB: Channel aggradation and morphologic change following 19th century hydraulic gold-mining in the Sierra Nevada, California, differed substantially between the lower Feather and Yuba Rivers. These differences can be explained in part by topographic position in the Sacramento Valley but also by differences in early 20th century engineering structures and management policies. Both rivers experienced extreme aggradation by mining sediment and substantial avulsions but the timing and mechanics of channel adjustments were dissimilar, in part due to varying strategies in river-training and flood control. River engineering and management in the late 19th century identified the lower Yuba River as a repository zone where mining sediment could be sequestered to reduce deliveries to navigable rivers downstream. Levees were set back up to 4 km allowing formation of a multi-thread channel system across a broad floodplain that is now deeply buried by mining sediment. In contrast, levees along the lower Feather were given narrow spacings to encourage self-scouring of channels and promote navigability of channels. The lower Feather River drains a larger basin and has a lower gradient than the Yuba River. Construction of Fremont Weir across the mouth of the Yolo Basin raised flood levels in the lower Feather River and may have reduced transport of bed sediment. This could explain the persistence of large sand sheets at and below the Bear River confluence. Data from historical maps, topographic surveys, aerial photographs, and 1999 LiDAR swath mapping are used to document and contrast channel changes and floodplain evolution between these two rivers. Topographic changes derived by differencing detailed 1906-1909 topographic maps and 1999 LiDAR data indicate substantial channel morphologic changes including channel filling, lateral migration, and evolution towards single-thread channel systems. Modern streambank stratigraphy reflects the differences in channel responses. Sites where channel avulsions moved the channel to its present position often have high banks of pre-historic soil with only a thin cap of historical alluvium at the top. In contrast, sites near original channel positions often have thick deposits of historical alluvium. These differences are key to understanding spatial patterns of storage of historic sediment which contains high concentrations of elemental mercury.
UR: http://people.cas.sc.edu/ajames/sacvalley.data/
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1640 Remote sensing (1855)
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
SC: Hydrology [H]
MN: 2007 Fall Meeting