HR: 1340h
AN: H53B-0462    [Abstracts]
TI: Can Interlocked Grains Reduce the Mobility of Gravel Bed Rivers?
AU: * Wydzga, A M
EM: wydzga@umail.ucsb.edu
AF: Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106 United States
AU: Hassan, M A
EM: mhassan@geog.ubc.ca
AF: Department of Geography, University of British Columbia, Vancouver, B.C V6T 1Z2 Canada
AU: Venditti, J G
EM: jgvenditti@yahoo.ca
AF: Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA 94720 United States
AU: Dunne, T
EM: tdunne@bren.ucsb.edu
AF: Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106 United States
AB: Channel stability of gravel bed rivers is enhanced by coarsening and structural modification of the bed, which determines the bed's resistance to entrainment, and hence the mobility of particles on the bed. In this study we propose a grain-scale classification system that qualitatively and quantitatively describes grain-to-grain interactions of fluvially re-worked gravel beds. The quantitative measure takes the form of the ratio of the vertical plucking force (Fv) required to remove a grain from a static, dry bed to the weight of the grain (Fw). Fv/Fw is an empirical measure of the restraining effect of neighboring grains and can range between 1 when the bed is loosely packed to >> 1 when the grains are interlocked. Preliminary results from a large (30 m long and 0.86 m wide) flume channel suggest that individual grains range from being loosely arranged on the bed (mean Fv/Fw approx. = 1) to highly packed or interlocked grains (mean Fv/Fw approx. = 5). Preliminary data from ephemeral rivers suggests a mean Fv/Fw ratio of approximately 3. Other packing arrangements observed and measured both in the flume and in the field include imbricated, embedded, and partially buried grains. These results suggest that the equations for predicting the mobility of coarse heterogeneous sediments may require reexamination before application to channels downstream of dams and in other low sediment supply channels where tight interlocking is expected to occur.
DE: 1808 Dams
DE: 1813 Eco-hydrology
DE: 1825 Geomorphology: fluvial (1625)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: Fall Meeting 2005