Scholarly article on topic 'Textural Characterization of Coastal Sediments along Tamil Nadu Coast, East Coast of India'

Textural Characterization of Coastal Sediments along Tamil Nadu Coast, East Coast of India Academic research paper on "Earth and related environmental sciences"

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{"Grain Size" / "Weight Percentage" / Mean / Skewness / Kurtosis / Gradistat / Tri-plot.}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — Sathish Sathasivam, R.S. Kankara, S. Chenthamil Selvan, Manikandan Muthusamy, Arockiaraj Samykannu, et al.

Abstract Particle size characterizations of beach sediments along Tamil Nadu coast was carried out in the present study. The main objective of this work is to identify the textural behaviour of beach sediments and how wave energy correlates with grain size distribution. To achieve this goal tri-plot analysis was performed. Grain size characteristics such as central tendency, kurtosis and skewness were estimated using an updated version of the GRADISTAT programme and discussed in this paper. The highest sediment samples having medium sand with unimodal and bimodal characters at all along the coast. The entire coastal area was characterized as well sorted, moderately well sorted and moderately sorted sediment environments. Sediments were identified as fine skewed to coarse skewed with platykurtic, mesokurtic and leptokurtic characters. Grain characteristics varied spatially and temporally along with beach orientation, foreshore slope withwave action and skewness correlates with shoreline changes. In some coastal tract having the negative skewness along the study region, but not very significant. The study depicts that the sedimentary coastal environment were influenced by the relatively medium wave action and some places were observed high wave action. From this study, it was concluded that the beach erosion, accretion, and stability of beaches are controlled by strong hydrodynamic and hydraulic process.

Academic research paper on topic "Textural Characterization of Coastal Sediments along Tamil Nadu Coast, East Coast of India"

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Procedía Engineering 116 (2015) 794 - 801

Procedía Engineering

www.elsevier.com/locate/procedia

8th International Conference on Asian and Pacific Coasts (APAC 2015)

Textural Characterization of Coastal Sediments along Tamil Nadu

coast, East coast of India.

Sathish Sathasivama, R.S.Kankaraa, S. Chenthamil Selvana, Manikandan Muthusamya, Arockiaraj

Samykannua and Rajan Bhoopathia

aMinistry of Earth Sciences,ICMAM - Project Directorate, NIOT Campus, Chennai- 600 100, India

Email:athi_geo@yahoo. co. in

Abstract

Particle size characterizations of beach sediments along Tamil Nadu coast was carried out in the present study. The main objective of this work is to identify the textural behaviour of beach sediments and how wave energy correlates with grain size distribution.To achieve this goal tri-plot analysis was performed. Grain size characteristics such as central tendency, kurtosis and skewness were estimated using an updated version of the GRADISTAT programme and discussed in this paper. The highest sediment samples having medium sand with unimodal and bimodal characters at all along the coast. The entire coastal area was characterized as well sorted, moderately well sorted and moderately sorted sediment environments. Sediments were identified as fine skewed to coarse skewed with platykurtic, mesokurtic and leptokurtic characters. Grain characteristics varied spatially and temporally along with beach orientation, foreshore slope withwave action and skewness correlates with shoreline changes. In some coastal tract having the negative skewness along the study region, but not very significant. The study depicts that the sedimentary coastal environment were influenced by the relatively medium wave action and some places were observed high wave action. From this study, it was concluded that the beach erosion, accretion, and stability of beaches are controlled by strong hydrodynamic and hydraulic process.

© 2015TheAuthors.PublishedbyElsevierLtd.Thisisan open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer- Review under responsibility of organizing committee , IIT Madras , and International Steering Committee of APAC 2015 Keywords:Grain Size, Weight Percentage, Mean, Skewness, Kurtosis, Gradistat, Tri-plot.

1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer- Review under responsibility of organizing committee , IIT Madras , and International Steering Committee of APAC 2015 doi:10.1016/j.proeng.2015.08.366

1. Introduction

Grain size is the one of most significant physical property of sediment and commonly used parameterfor understanding the processes involved in transportation and deposition of sediments (Inman, 1952; Folk and Ward, 1957; Mason and Folk, 1958; Friedman, 1961; Krumbein and Sloss, 1963; Nordstrom, 1977). Some of the pioneering studies on grain size characteristics are still referred by many researchers. Grain-size parameters are required and the mean size of medium to very coarse silt has proved to be a useful measure of the speed of the depositing flow(McCave, 2008). Geologist employs the sediment particle size data to study the trends of surface processes related to the dynamic conditions of transportation and deposition. Engineers apply grain size to revise sample permeability and stability under load. In the great majority of cases, this has been for non-cohesive sands and gravels. Hydrologists use it when studying the movement of subsurface fluids (McCave and Syvitski, 1991). The objectives of a grain-size analysis are to accurately measure the individual particle sizes to determine their frequency distribution, and to calculate a statistical report that effectively characterizes the samples. In this study, an attempt has been made to analyse the beach sediment characterstics along Tamil Nadu coast.

2. Study Area

The study area covers 950 km coastline between Kalpakam to Colachal in Tamil Nadu (TN), covering 11coastal districts(Figure.1). The coastline is endowed with various geomorphologic features. The coastal zone is under development pressure and coast is experiencing a range of management problems including shoreline erosion. About 42% of TN coast is facing erosion. The mean tidal range varies between 0.6 m - 1.5 m. and average wave height varies from 0.3m-l.8m.

Figure 1: Map of the study site showing the sampling locations.

Tamil Nadu is having a two-monsoon system viz. Southwest summer monsoon (June to September) and the Northeast monsoon (October to December). Coastal Tamil Nadu receives about 60% of its annual rainfall and interior Tamil Nadu receives about 40-50% of annual rainfall during the northeast monsoon. The beaches and beach ridges along the southern division of the east coast of India around Tirunelveli, Kanyakumari and

Manavalakurichi are occurred with economically viable placer deposits (Loveson, 1993; Bruckner, 1988). These deposits are economically feasible and being mined in many places and brings revenue for our country. The sediment ofcoastalareahave age ranging from Late Pleistocene to Recent(Chauhan, 1989).

3. Materials and Methods

One sixty five sediment samples were collected during the month of August, 2013from the backshore, bermline and foreshore of Tamil Nadu coastal prefecture. Hereafter backshore, bermline and foreshore are BS, BL, and FS respectively. Concurrently positioning of samples was conducted by using handled GPS. Samples were carefully preserved in polythene bags and they brought into the ICMAM-PD sedimentology lab. In the laboratory, dead shells were separated from sediments and the mixed saline content was removed from the grains by washing with water. The grain size distribution was carried out by using a sieve shaker and it is consisting of 8 sieves containing mesh sizes 75^m, 125^m, 180^m, 250^m, 355^m, 500^m, 1000^mand 2000^m.

250 500

750 1000 1250 1500 1750 2000

Garin size(^m)

backshore backshore backshore backshore backshore backshore backshore backshore backshore backshore backshore backshore backshore backshore backshore

a? 50 £ 40 30 * 20 10 o

250 500

750 1000 1250 1500 1750 2000

Grain size(^m)

bermline bermline bermline bermline bermline bermline bermline bermline bermline bermline bermline bermline bermline bermline bermline bermline

70 60 50 40 . 30 20 10 0

250 500 750 1000 1250 1500 1750 2000

Grain size(^m)

foreshore foreshore foreshore foreshore foreshore foreshore foreshore foreshore foreshore foreshore foreshore foreshore foreshore foreshore foreshore foreshore

Figure 2: Weight % curves of samples

The sediment distribution is presented graphically as weight percentage curves of backshore (Figure.2a), bermline (Figure.2b) and foreshore (Figure.2c). The statistical parameters such as mean, standard deviation, skewness and kurtosis were computed by (Folk and ward, 1957) using the GRADISTAT grain size distribution and statistical package (Blott and Pye, 2001).

3.1. Measurements of Statistical properties

Sediments have many imperative characteristics of which particle size is only one. Particle size refers to the sizes of all of the particles in sediment. If you compute the mean particle size, this does not tell you about the range of sizes occurring. If you estimate a range, this does not tell you the shape of the distribution, which might be normal or strongly skewed to coarse or fine particles. Mean is the arithmetic average size of the sediment and is expected to be influenced by source of supply, transportation and environment of deposition.

4.Result

The parameters used to describe the particle size distribution fall into four primary groups: those are the mean, standard deviation (sorting), skewness and kurtosis. These parameters can be easily acquired by mathematical or graphical methods. The mathematical 'method of moments' (Krumbein and Pettijohn, 1938; Friedman and Johnson, 1982) is the most accurate since it represented the entire sample population. However, consequently the statistics are greatly affected by outliers in the tails of the distribution, and this form of analysis should not be used unless the size distribution is known (Mcmanus, 1988). The grain size parameters of the study area and statistical properties of grain sizes and its interpretations are shown in figures 3-6. Standard deviation of most of the backshore samples emerge well sorted to moderately sorted (1.29 to 1.79), mean values indicating medium sand to coarse sand (135.60 to 807.10), skewness values having symmetrical to coarse skewed (-0.25 to +0.36) and kurtosis values depicts mesokurtic to leptokurtic (0.82 to 1.49). The bermline values conquered that moderately well sorted to well sorted, mean values dominating from fine sand to medium sand and the skewness is symmetrical to coarse and kurtosis occurred in all types. In foreshore, standard deviation values implying moderately well sorted to well sorted (1.2 to 1.98),the meanvalue indicating fine sand to medium sand (130.00to 490.80), the kurtosis depicts platykurtic to leptokurtic (0.84 to 1.69). Friedman (1962) suggested that extreme high or low values of kurtosis imply that part of the sediment achieved its sorting elsewhere in a high energy environment. The skewness is varying coarsely skewed to fine skewness (+0.55 to -0.35). The negative skewness values indicate coarse-skewed material, whereas the positive values represents more material in fine skewed. Fine sediments were found in the northern part(Kalpakkam to Kodiakarai) of the study area because of the prevailing high wave energy condition. This is also evidenced by the erosive action of the waves (Rajamanickam et.al., (1995) reported high energy condition is also attributable to the presence of submarine canyons in the Pondicherry and Cuddalore regions. Numerous factors influenced to textural characteristics of coastal sediments. They are composed of neighbouring lands, climatic condition of that area, tide, littoral transport, length and energy of sediment transport, redox conditions in the depositional environments (Bhatia and Cook, 1986; Fralick and Kronberg, 1997; Anithamary et.al., 2011). Moreover, spatial dissimilarity in sediment composition can help to determine the present environmental conditions. Statistical methods are commonly employed to simplify the necessary comparisons among samples and quantify the observed differences. Sedimentologists follow to describe particle distributions by mathematical moments (Krumbein and Pettijohn, 1938) and inclusive graphics (Folk, 1974) and statistical methods. In this context, the particle distribution is used for grain size analysis.

0.0 ...........................

13 5 7 9 1113 1517192123252729313335373941434547 49515355

Sample number

Figure 3: Standard deviation of BS, BL, FS

Figure 4: Mean of BS, BL, FS

Figure 5: Kurtosis of BS, BL, FS

Sample number

Figure 6: Skewness of BS, BL, FS

5. Discussion

The weight percentage distribution curves show that the grain size variation was more along foreshore due to the effect of wave activity compared to bermline. The statistical properties of sediment samples illustrate that unimodal and bimodal character is dominated in the backshore, bermline and foreshore along the study area. The backshore sediments predominantly having the medium sand with moderately well sorted to well sorted samples. In bermline samples, the fine sand to medium sand with moderately well sorted and well sorted was found. In foreshore, mainly fine sand to medium sand and moderately sorted to moderately well sorted was observed. The range of kurtosis values more or less same from samples 1-23 (northern part) and sample from 23-55 (southern part). The 29% (16 nos) of backshore samples are negatively skewed, while 31% (17 nos) bermline samples are negatively skewed. However, the foreshore samples have relatively lower 24% (13 nos) negatively skew specimens. The study showed that the negatively (coarse) skewed and positively (fine) skewed samples, indicating strong deposition and erosion tendency along the study region. The negative skewness was correlated with the long

term shoreline change (1990-2014) result. It was observed that the eroding locations such as Vyalikuppam, Ganapathychettikulam,Chinnamudhaliyarchavadi,Pombuhar,Tharangapadi, Mimisal, Muthaipuram and Periyathalai (Kankara and Selvan, 2012) had similar trend of skewness. The results of shoreline changes v/s negative skewness for foreshore locations are shown in figure 7. In addition, to understand the hydrodynamic process such as wave with particle size distribution, unconventionally the tri-plot (Figure. 8) method was also adopted. From the tri-plot analysis, in backshore area, Central part of the Tamil Nadu coast, having fine sand, Southern part of Tamil Nadu has medium sand and Northern region of coastal zone has coarse sand. Whereas in bermline, Central part of the Tamil Nadu coast possesses fine sand, Southern part of Tamil Nadu has medium sand and Northern side consists of coarse sand. In foreshore zone, Northern side comprises fine sand and the Southern side is dominating the medium sand. The above finding is closely matched with the wave distribution pattern from south to north of Tamilnadu coast (Sivakokholandu et.al., 2014) where the significant wave height is showing a decreasing trend from Kanyakumari to Pondicherry

Figure 7: Comparison of measured shoreline change and skewness values where erosion is prominent.

Figure 8: a)tri-plot for textural analysis of all sediments, b)Different type of sands, c)Foreshore samples,

d)Backshore samples, e)Bermline samples

6. Conclusion

In order to conclude the discussion above which reveals that surface sediment properties of the TN coastal area, their major inputs and their main transport, depositional processes. Geomorphology and climatic conditions play a crucial role to control the sediment dynamic nature of the study area. The northern part of TN coast starting from Kalpakkam to Kodiakarai having fine sand with high energy condition existing, central coast begins with Kodiakarai and ended with Mandapamincluding Rameshwaram was dominated by medium sand with less energy condition and similar feature also observed in the southern part from Mandapam to Kanyakumari.

Acknowledgements: Authors would like to thank Dr.Shailesh Nayak, Secretary, Ministry of Earth Sciences, Government of India and Dr. M.A. Atmanand, PD-ICMAM for their keen interest, encouragement and provided facilities for this study.

7. References

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Blott, S.J., Pye. K., 2001. GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments. Earth Surface Processes and Landforms, Vol. 26, No 11, 1237-1248.

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