Hydrodynamic Processes and Heavy Mineral Deposits of the Southwest Coast, India (original) (raw)
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Hydrodynamic processes and heavy mineral deposits of the southwest coast of India
Journal of Coastal Research
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.
Nearshore and Beach Sedimentary Dynamics in a Placer-Dominated Coast, Southwest India
Journal of Coastal Research, 2007
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.
1999
The present study on the heavy mineral assemblage from the sediments of beaches was made in order to understand the spatial, seasonal and longshore distributions, source of the sediment (Provenance) and the sediment movement. The study has indicated the presence of Magnetite, Ilmenite, Hornblende, Tourmaline, Sillimanite, Rutile, Garnet, Zircon. Kyanite etc.; they are enriched in finer sand fractions. The heavy mineral assemblage of this stretch indicates the mixed provenance of Igneous and Metamorphic rocks with reworked sediments especially at Belekeri bay beaches.
BEACH SEDIMENT CHARACTRISTICS OF VELNESHWAR BEACH, RATNAGIRI, MAHARASHTRA
Arts , Science and Commerce College Kolhar, Rahata Ahemadnagar , 2019
Grain size parameters provide an insight in to the nature and the energy flux of the multivarious transporting agents and their purview of depositional environment. This helps in understanding the various processes effecting erosion and deposition. Differentiation of depositional environments has been carried out based on size distribution of sedimentary particles. Surface texture of sand sized quartz grains with SEM technique has emerged in to a major approach for interpreting sedimentary environment and transport mechanism. The study is in line with the guidelines on the studies of shoreline changes in the Eastern African region, as well the study of the Eastern African database of coastal resources. The former has recommended detailed studies of shore morphological features, with updating of old information, while the later has recommended establishment and updating databases of coastal resources for the purpose of sustainable management of the existing resources. To explore the sandy beach sorting and sedimentary characteristic induced by wave action, a set of 2D wave flume experiments on a sandy beach were performed. The initial beach slope with non-uniform sand of combination of 1/10 and 1/20 was exposed to regular waves, random waves, cnoidal waves and solitary waves respectively. The evolution of cross-shore beach profiles and the grain size of sediments in different locations were measured and recorded. Experimental results show that the sediments of sandy beach under wave action produced obvious sorting phenomenon. The intense turbulence generated by breaking waves leads to the sediment-transporting, and provides the impetus for the movement of fine sands. Course sands deposited in intense turbulence deposition area because of carrying capacity of the flow is not enough due to turbulence effect. Fine sands were carried by the flow induced by breaking waves, and separately deposited in the area of weak turbulence. Significant salinity intrusion has been observed in the Pangani estuary, and this again has been related with the increased water abstraction, mainly due to irrigation along the Pangani catchment.
Equilibrium profile is one of the conce pts in coastal geomorphology which is a result of the balance of destructive versus constructive forces. Two e quilibrium be ach profile models, viz. Bruun/Dean's twothirds power mode l and modified Bodge expone ntial model were used to analyse the measured post-monsoon (winter) beach profiles from three beaches in Goa having varying coastal morphology settings. The major factors that affect the equilibrium beach profile, viz. the me dian grain size (D 50 ) and the profile shape factor m, which are inve rsely proportional to each othe r, have been analysed for their application to the study site. Also, the variation of these two parameters with beach slope and grain size is studie d. Longshore sedime nt transport rates (LSTRs) are estimate d at these three beaches from the littoral environme ntal observations. LSTRs show that during winte r months, the net transport is of the orde r of 10.83 10 6 m 3 /year (southe rly transport) and 9.02 10 6 m 3 /year (southerly transport) respectively, at Candolim and Ke ri beaches, whe reas it is about 0.62 10 6 m 3 /year (northerly transport) at Miramar. This article discusses the methods used and results of measure me nts of beach morphology, LSTRs, analysis of equilibrium profiles and influe nce of various paramete rs relate d to equilibrium profiles.
Sediment Texture and Geochemistry of Beaches between Redi-Vengurla, Sindhudurg, West Coast of India
Journal of Coastal Research, 2017
Textural and geochemical determinations were carried out on three beaches (Vengurla, Aravali, and Redi) of the Sindhudurg district, Maharashtra, west coast of India. Seasonal sediments from the beach were collected during 2003-04 to understand the sediment dynamics (texture, dispersal pattern, depositional environment, etc.) and geochemical characteristics. In general, a seaward grain size fining is seen along Vengurla beach (swash-backwash phenomenon), with a coarsening seaward trend along Aravali and Redi beaches (high-energy conditions). The CM pattern studies reveal traction currents as the transport mechanism. Thus, the sediments of the study area are deposited under moderate to high-energy conditions. The geochemical study shows that the percentages of V, Cr, and Zr are greater in
Seasonal Variation of Beach Sediment Dynamics of the Coleroon Coast, Tamil Nadu, India
International Journal of Earth Sciences and Engineering
The present study was carried out in order to study about the textural characteristics of sediments, and their seasonal changes along the coast of Coleroon. Samplings were done at different station during two seasons from monsoon 2009 to postmonsoon 2010. Granulometric studies reveals that the grain size parameters at different beach locations do not suggest a general trend of longshore variations, except on the beach close to the river mouth. The differences between the seasons were larger than those between the geomorphological units. During the monsoon the mean size was medium, sorting was worse and the distribution was more positively skewed. The major part of the sediment fall in a medium to fine grained category.
Seasonal (post-and pre-monsoon) changes in texture and environment of deposition of beach sediments of Karnataka coast have been studied using various statistical parameters (Mean size, Standard deviation, Skewness and Kurtosis). These parameters were obtained for all the sieved sediment samples (68 for each season), using Gradistat V8.0 and G-Stat software packages. Based on the range of variability of these statistical parameters, the studied coast has been divided into four sectors. Sector I extends from Talapady to Surathkal; sector II includes beaches from Mukka to Kota. Sector III comprises Marvanthe and Nesther beaches and those lying between Murdeshwara and Devbagh fall in sector IV.Passega's CM and Tractive current diagrams were prepared to understand the energy condition of depositional currents and mode of transportation of sediment respectively. Linear Discriminant Function (LDF) plots were used to understand the environment of deposition of sediments. TheCM diagram reveals predominance of beach and tractive currentconditions along the entire coast. The Tractive current diagram indicates that deposition of sediment takes place by rolling and bottom suspension during post-monsoon, whereas by graded suspension and no rolling conditions during pre-monsoon season in sector I. In sector II, deposition of sediment takes place by bottom suspension and rolling during both the seasons. In sector III, the sediments show change in energy conditions with time where they are deposited by rolling during post-monsoon, whereas prevailing of low energy condition during pre-monsoon season as deposition of sediment takes place by bottom suspension and rolling. In sector IV, bottom and graded suspensions have been the dominant mode of deposition during both the seasons. The LDF analysis of sediment samples indicates dominance of shallow marine environment of deposition for both the seasons. The LDF plotsreveal that sector I predominantly belongs to beach shallow to beach littoral environment for both the seasons. Shallow marine agitated environment of deposition was observed for the postmonsoon season in sector II, while increase in energy conditions at this sector led tobeach shallow environment of deposition during the pre-monsoon season. Sector III shows predominance of beach littoral environment of deposition for the post-monsoon, while beach shallow environment of deposition during the pre-monsoon indicating decrease in energy conditions. Sector IV plots show little or no change for both the seasons and the samples predominantly fall in shallow marine agitated environment of deposition.
Textural characteristics of beach sediments along Kalpakkam, south east coast of India
2017
Samples collected from foreshore region showed more variations in grain size as compared to mid-shore region samples. Median values varied from-0.08ø to 2.19 ø with an average of 1.04 ø (Std ± 0.65 ø). Mean value showed that samples were fine to coarse sand, whereas, only 1.8% of total samples were found as very coarse sand. During southwest monsoon the average mean size of the beach sediment was 0.98 ø, which is coarse sand in contrast to the medium sand observed during other seasons. Present study showed that, 81.7% of the samples were unimodal and 17.8% samples were bimodal. Sediment samples were very well sorted (0.18 ø) to poorly sorted (1.18 ø) and sorting characteristics decreased with increased wave energy. Skewness value indicated that 41% & 11% of the samples were positively skewed and negative skewed respectively, whereas, rest of the samples were symmetrical. All the beaches were dominated by mesokurtic sediment. Dominance of positively skewed sediment in the study area indicated the prevalence of low wave activity and longshore current. Presence of relatively high fraction of mesokurtic sediment indicated that the beaches along Kalpakkam by and large have uniform energy environment.