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Hydrodynamic Processes and Heavy Mineral Deposits of the Southwest Coast, India

N.P. Kurian, T.N. Prakash, F. Jose and K.P. Black
Journal of Coastal Research
Special Issue 34. International Coastal Symposium (ICS 2000): CHALLENGES FOR THE 21ST CENTURY IN COASTAL SCIENCES, ENGINEERING AND ENVIRONMENT (August 2001), pp. 154-163
Stable URL: http://www.jstor.org/stable/25736284
Page Count: 10
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Hydrodynamic Processes and Heavy Mineral Deposits of the Southwest Coast, India
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Abstract

The beaches of Chavara and Manavalakuruchi of the southwest coast of India have rich heavy mineral concentrations with distinctive spatial and temporal distributions. Both locations exhibit high concentrations of heavy minerals on the northern sides of the headlands, with practically no concentration on the southern sides. Cross-shore, the sediments become less rich in the heavy minerals offshore. During the rough monsoon when the winds are onshore the concentration of heavy minerals along the mid-tide line of the beaches is considerably higher than during the calm non-monsoon when swell prevails. The concentrations of heavy minerals alongshore were highest in zones where the beach with relict sediments of high mineral content is eroding. We find that the patterns observed in the heavy minerals along the Chavara coast can be explained by a single hypothesis dependent on the presence of a source and the winnowing of the more easily entrained low-density fractions. The pattern appears to be slightly different for Manavalakuruchi coast where the zone of hundred percent enrichment is adjacent to the river mouth, indicating an additional source of river input. Analysis of wave and current data showed the dominant role of waves over coastal currents in the transport of these sediments and the wave-induced thresholds for initiation of motion indicated that the heavy component is less easily moved than the white sand (quartz) constituent. We suggest that the patterns can be explained by winnowing of the white sands from the eroded beach sediments during the stormy monsoon leaving higher enrichment at the beach. In the swell period of the post-monsoon, the erosion ceases as the asymmetric swells re-establish the beach, bringing proportionally more of the more-easily entrained white sediment shorewards, thereby explaining the reduced enrichment at this time. The cross-shore reduction in heavy minerals may be simply explained as an inverse relationship to distance from the beach source. The longshore distribution is a response to the presence of the source of black sands on the northern sides of the headlands. The headlands may simply act to isolate the source, thereby explaining the tendency for high concentrations on one side only.

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