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1 November 2007 Nearshore and Beach Sedimentary Dynamics in a Placer-Dominated Coast, Southwest India
T. N. Prakash, K. P. Black, J. Mathew, N. P. Kurian, K. V. Thomas, T. S. Shahul Hameed, M. V. Vinod, K. Rajith
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Abstract

The suspension and enrichment of heavy sands at Chavara, southwest coast of India, were examined by studying the beach and nearshore sedimentology, mineralogy, fall velocity patterns, bed reference concentrations, and mixing length characteristics. The outer shelf is carpeted with sand mixed with silty-clay sediments. On the inner shelf, the coarse fraction of the heavy sands increases near the coast, whereas the finer fraction spreads more evenly right across the shelf, to both the south and north of Chavara. The beach is composed mainly of medium to fine sand. Seasonally, beach sediments are poorly sorted during the postmonsoon, and settling velocity measurements indicated that sediment grain size was coarser at this time than during the monsoon period. Further, the beach face becomes enriched with heavy sands, with a corresponding loss of quartz sands, during erosive monsoonal events. A bimodal coarse population of mixed colour of black and white arrived at the beach after the monsoon. Although sediment trap data exhibited maximum sedimentation during the monsoon, sediments on the inner shelf out to an 8-m depth were highly mobile because of waves and currents throughout the year. A log-linear concentration profile was found with the sediment traps, and the grain fall velocities decreased with elevation. The evidence suggests that the postmonsoon coarse fraction comes from the inner shelf, with denser minerals near the bed moved most effectively toward shore. This may occur because of wave asymmetry causing shoreward near-bed sediment migration of the denser sands during the clean swells of the post monsoon. The finer sands, which penetrate higher in the water column, are not subject to bedload asymmetrical transport and so they are relatively absent from the beach when the heavier sands start arriving in the postmonsoon.

T. N. Prakash, K. P. Black, J. Mathew, N. P. Kurian, K. V. Thomas, T. S. Shahul Hameed, M. V. Vinod, and K. Rajith "Nearshore and Beach Sedimentary Dynamics in a Placer-Dominated Coast, Southwest India," Journal of Coastal Research 2007(236), 1391-1398, (1 November 2007). https://doi.org/10.2112/04-0391.1
Received: 11 January 2005; Accepted: 1 October 2005; Published: 1 November 2007
KEYWORDS
Beach
beach placers
enrichment
Nearshore
sediment traps
southwest coast of India
Suspension
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