HR: 16:15h
AN: OS24A-02    [Abstracts]
TI: Bedform Migration and Bed Envelope Statistics
AU: * Gallagher, E L
EM: edith.gallagher@fandm.edu
AF: Franklin and Marshall College, PO Box 3003, Lancaster, PA 17604 United States
AU: Holman, R
EM: holman@coas.oregonstate.edu
AF: Oregon State University, COAS 104 Ocean Admin Bldg, Corvallis, OR 97331-5503
AB: The generation and migration of bedforms (ripples, megaripples and sand bars) on sandy bottoms in the nearshore (0-8 m water depths) provides a mechanism whereby objects on the seafloor can become buried. As a bedform migrates past an object, the object will fall to the low point of the bedform trough and be buried by the passage of the following bedform crest. Existing data sets are being used to examine the temporal evolution of the bottom profile envelope at fixed locations. The maximum envelope thickness, D$_{max}$, is defined as the difference between the maximum and minimum extent of the bed during a given time window (4 day- to 12 year-windows are used in this study). D$_{max}$ is hypothesized to grow as an exponential taper (quickly at first, then slowing and approaching an asymptotic value) as the time window increases and this is observed. However, envelope thickness takes a long time, 2-6 years, to level off and approach an asymptotic value. Both megaripples and larger-scale morphological changes (eg, bar migration) affect D$_{max}$. Envelopes owing to megaripple migration grow quickly, reaching a maximum of $<$ 50 cm within about 8 days. Bar-scale erosion and accretion generates envelopes that are larger (1-3 m depending on cross-shore location) and grow slowly. To examine burial of objects on the bed, W is defined as the vertical scale of an object and is compared with the instantaneous elevation of the seafloor above envelope minimum. When D exceeds W, an object on the bed will be buried. The likelihood of burial is being examined at the end of set time windows. Percent burial is shown to increase with time and to decrease in deeper water.
DE: 4546 Nearshore processes
DE: 4558 Sediment transport
DE: 3020 Littoral processes
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting