. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography Shelf Sedimentation 129 lands are flooded. Gravel and coarse sand are deposited as a substratum of braid bars and mean- der point bars, respectively, and are veneered with a top stratum of overbank clays. Silt undergoes temporary deposition in levees in the lower flood- plain, but these tend to be undermined, so that their deposits reenter the transport system. Thus the floodplain environment serves as a skewed bandpass filter, with preferential byp
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography Shelf Sedimentation 129 lands are flooded. Gravel and coarse sand are deposited as a substratum of braid bars and mean- der point bars, respectively, and are veneered with a top stratum of overbank clays. Silt undergoes temporary deposition in levees in the lower flood- plain, but these tend to be undermined, so that their deposits reenter the transport system. Thus the floodplain environment serves as a skewed bandpass filter, with preferential bypassing of the medium grades, entrapment of some fines over bank, and much coarse material deposited in channel axes. This process continues through the tidal swamp environment, where the entrapment of fines dominates. Reversing tidal flows generate vel- ocities of 40-180 cm/sec in tidal creeks, enough to move sand and gravel. Entrapment of fines over- bank in the mangrove swamps is enhanced by the phenomena of slack high water and the prolonged period of reduced velocity associated with it. Fines then deposited begin to compact, and require great- er velocities to erode them than served to permit their deposition. Major channels, which pass through the inter- tidal environment to the sea, must store their coars- er sediment during low-water stages at the foot of the salt wedge, where the landward-inclined sur- face of zero net motion intersects the channel floor. During high-water stages, stored bottom sediment must be rhythmically flushed out of the estuary mouth by the tidal cycle. Sand coarser than the effective suspension threshold of 230 microns (Bag- nold, 1966) will be deposited on the arcuate estuary mouth shoals (Oertel and Howard, 1972), where, after a prolonged period of residence in the sand circulation cells of the shoal, it leaks into the downcoast littoral drift system. Finer sand is en- trained into suspension by large-scale top-to-bottom turbulence in the high-
Size: 1614px × 1549px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionamericana, booksponsorlyrasismemb
