HR: 14:25h
AN: H53D-04    [Abstracts]
TI: Experimental Study of Sinuous Channel Evolution Associated with Depositional Turbidity Currents
AU: * Straub, K M
EM: kmstraub@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave BLDG 54-824, Cambridge, MA 02139
AU: Mohrig, D C
EM: mohrig@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave BLDG 54-824, Cambridge, MA 02139
AU: Buttles, J
EM: buttles@erl.mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave BLDG 54-824, Cambridge, MA 02139
AB: We present results from a laboratory experiment documenting the evolution of a sinuous channel form via sedimentation from a series of 24 turbidity currents. An original channel was built using a sine-generated curve to describe its planform. Wavelength and amplitude of this curve were 2.27 m and 0.39 m, respectively, producing a channel with 3 bends and a sinuosity of 1.23. Initial thickness for each current was 0.10 m, the depth of the original channel form, and the mean streamwise velocity was 0.07 m/s. Sediment suspended in each current consisted of silica with particle diameters between 5-120 ŸYm and a median grain size of 30 ŸYm. Sedimentation patterns differed from those common to terrestrial channels. In particular, sedimentation in the channel was greatest on the outer banks of bends. This lead to a reduction in sinuosity as the channel aggraded vertically, a pattern commonly observed in acoustical surveys of submarine channels on continental slopes worldwide. The primary reason for this style of channel evolution was the small excess density of the laboratory currents, 3.8%, relative to the ambient fluid, water. This small density difference lead to a fraction of the confined flow running up and out the channel at the outer bank of each bend and to an exaggerated super-elevation for the remaining channelized current. Sedimentation within the channel was 3-4 times greater along the outer bank than the inner bank of bends, altering cross-sectional geometry with each flow. Deposition on the channel bottom reduced channel relief and increased the fraction of each current exiting the channel at the outer banks of bends. At all bends the coarsest deposit was found high on the outer wall of the channel at the levee crest. Grain size decreased systematically moving down from this position into the channel thalweg and then onto the inner channel bank. Deposition rates on the outer levee crest were 30-70% of deposition rates on the channel bottom at the first bend. The ability of turbidity currents to partially exit the channel at bends resulted in focused levee growth, reducing the rate at which channel relief decreases through time. This feedback provides an explanation for the observed persistence of strongly aggrading sinuous channels in the submarine environment.
DE: 1815 Erosion and sedimentation
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting