Seasonal Variation in Textural Characteristics and Sedimentary Environments of Beach Sediments, Karnataka Coast, India Academic research paper on "Earth and related environmental sciences"

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Aquatic Procedia 4 (2015) 117 - 124

INTERNATIONAL CONFERENCE ON WATER RESOURCES, COASTAL AND OCEAN

ENGINEERING (ICWRCOE 2015)

Seasonal Variation in Textural Characteristics and Sedimentary Environments of Beach Sediments, Karnataka Coast, India

Sarang J.Kulkarnia,*,Praveen G. Deshbhandaria and K.S.Jayappaa

aDepartment of Marine Geology, Mangalore University, Mangalagangothri 574199, Karnataka, India

Abstract

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 GradistatV80 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 post-monsoon 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.

© 2015TheAuthors.PublishedbyElsevier B.V. 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 of ICWRCOE 2015

Keywords:Grain size;Beach sediment; Environment of deposition; Karnataka; India

* Corresponding author. Tel.: +91-986-075-2979 E-mail address:sarangkulkarni01 @gmail.com

2214-241X © 2015 The Authors. Published by Elsevier B.V. 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 of ICWRCOE 2015

doi: 10.1016/j.aqpro.2015.02.017

1. Introduction

Grain-size studies of beach sediments provide a wealth of information on the intrinsic properties of sediments and their depositional environment (Rajaganapathyet al. 2012). As being a dynamic zone where air, land and water interact, the coastal zone is a focus of particular interest among the scientific community. The complex coastal processes operated in the past and in the present have left their imprints in the sediments. In this regard, sedimentology of beach sediments plays a vital role in documenting the depositional history of a region. Pioneering studies were undertaken by Bascom (1951), Inman and Chamberlin (1955), Freidman (1967), Passega (1964), Visher (1969), Folk and Ward (1957) and others. Sedimentologists are particularly concerned with three aspects of particle size: (a) Techniques for measuring grain size and expressing it in terms of a grade-scale, (b) Methods for quantifying the grain size data and presenting them in a graphical and a statistical form, and (c) The genetic significance of these data. Systematic granulometric studies of east and west coasts of India have been carried out by many researchers (Rajamanickam and Gujar 1984, 1985, 1993; Chaudhariet al. 1981; Rao et al. 2005; Anguswamy and Rajamanickam 2006, 2007; Rajaganapathyet al. 2012).

2. Study Area

The study area extends over a distance of 300 km along Karnataka coast bounded by Talapady in the south and Devbagh in the north (12°46'43.5" N to 14°51' 23.3" N Lat. and 74°51' 28.7" E 74°06' 41.1" E Long.). There are three districts - DakshinKanada, Udupi and Uttar Kanada - along this coast and totally 25 locations have been chosen for sediment sampling (Fig. 1). This coast consists of long, narrow and straight open sandy beaches, spectacular spits, barrier beaches, estuaries, mud flats and few patches of mangroves along DakshinKanada and Udupi districts, on the other hand Uttar Kanada beaches are mainly crescent shaped, pocket beaches lying between rocky headlands (Jayappa and Vijaya Kumar 2006). The study area lies on basement gneisses which are overlain by

laterites and Recent alluvium brought by the west flowing rivers._

Location Map

Fig. 1: Location map of the study area showing various sectors and sediment sampling locations.

3. Materials and Methods

The sampling included collection of surface sediment samples along each beach profile from the foreshore, berm (mid-shore) and backshore during post-monsoon (October 2013) and pre-monsoon (March 2014). A total of 136 (68 for each season) samples were collected along the 25 beach profiles. Foreshore slope, beach orientation, and littoral environmental parameters - wave direction, wave breaker height, wave period, longshore current direction and speed - were also measured / recorded during sample collection.

All the sediment samples were dried in a hot air oven at 65°C, then size of the samples were reduced to ~100 gms by coning and quartering. These representative samples were then washed with distilled water to remove salt content and further treated with 1:10 parts of HCl to remove CaCo3 shells. In order to eliminate organic content, the sediment samples were treated with 30 % H2O2 (Ingram 1970). Later these samples were washed again with distilled water and dried inside hot air oven at 65°C.

After drying, the sediment samples were weighed again to calculate the loss of CaCo3 and the organic content. Then the samples were sieved on a Ro-Tap mechanical sieve shaker for 15 minutes using ASTM sieves at 0.500 intervals between mesh #5 and #230. The sieved samples were collected from all the sieves, weighed and packed separately for further analysis.

The grain-size data obtained after sieving is processed using software packages such as GradistatV80 and G-Stat. The Gradistat package was used to calculate all the statistical parameters such as Mean 0 size, Sorting (Standard deviation), Skewness and Kurtosis by Folk and Ward graphic method (1957). The Trivariate plots of these samples have been plotted showing relationship between the above mentioned parameters. The G-Stat software package was used for obtaining the CM diagram and Tractive current diagram (Passega 1964; Visher 1969). Linear discriminate function (Sahu 1964) was used for interpretation of energy and fluidity fluxes and depositional environment of the sediment.

4. Results and Discussion

The results of textural analysis reveal that 63% of the samples collected during post-monsoon are unimodal, 24% of them are bimodal and 13% are trimodal, whereas the pre-monsoon samples revealed that 88% of them are unimodal and only 12% are bimodal in nature. The textural attributes of sediment samples, viz Mean, Sorting, Skewness and Kurtosis show on an average moderately sorted and symmetrically skewed nature as revealed by Folk and Ward (1957).Based on the textural characteristics of the beach sediments, the study area has been divided into four sectors from south to north, starting from Talapady to Devbagh.

4.1.1. Sector //This sector comprises of seven beaches between Talapady and Surathkal (Fig. 1). The samples of this sector during the post-monsoon season, show a range of variation in mean phi size from max (0.4420) to min (2.0810) i.e. ranging from coarse to fine sand and moderately sorted to well sorted nature. Skewness values range from coarse skewed to fine skewed and Kurtosis values range from very leptokurtic to platykurtic in nature. Whereas, the sediments of pre-monsoon show a range of variation in the mean phi size from max (0.4130) to min (2.5490) i.e. ranging from coarse to fine sand and moderately sorted to well sorted nature. Skewness values range from very coarse skewed to fine skewed and Kurtosis values range from leptokurtic to platykurtic in nature (Folk and Ward 1957). The foreshore slope of this sector on an average was found to be steeper and as the slope of the beach increased the mean grain size also increased.

4.1.2. Sector ///This sector comprises of eight beaches between Mukka and Kota (Fig. 1). Sediment samples of this sector for the post-monsoon profiles, show a range of variation in the Mean phi size from max (1.320 0) to min (2.922 0) i.e. ranging from medium to fine sand and moderately well sorted to well sorted nature. Skewness values range from very coarse skewed to fine skewed and Kurtosis values range from leptokurtic to platykurtic in nature. The sediment samples of pre-monsoon profiles show a range of variation in the Mean phi size from max (1.0260) to min (2.5570) i.e. ranging from medium to fine sand and moderately well sorted to well sorted in nature. Skewness values range from coarse skewed to fine skewed with dominance of symmetrically skewed samples and Kurtosis values range from leptokurtic to platykurtic in nature. The foreshore slope is generally found to be significantly

gentler in this sector.

4.1.3. Sector ///.-This sector comprises of two beaches (Marvanthe and Nesther) (Fig. 1). The samples of this sector during the post-monsoon season, show a range of variation in Mean phi size from max (-0.1830) to min (1.8020) i.e. ranging from very coarse to medium sand and were moderately well sorted to well sorted in nature. Skewness values range from coarse skewed to fine skewed and Kurtosis values range from leptokurtic to platykurtic in nature. The sediment samples of pre-monsoon profiles show a range of variation in the Mean phi size from max (0.9000) to min (1.9200) i.e. ranging from coarse to medium sand and are moderately sorted to moderately well sorted nature. Skewness values range from coarse skewed to fine skewed and kurtosis values range from leptokurtic to mesokurtic in nature, with the foreshore slope getting steeper in this sector.

4.1.4. Sector /V:This sector comprises of eight beaches from Murdeshwara to Devbagh (Fig. 1). The samples of this sector during the post-monsoon season show a range of variation in Mean phi size from max (1.536 0) to min (3.0980) i.e. ranging from medium to very fine sand and moderately well sorted to very well sorted nature. Skewness values range from very coarse skewed to fine skewed and Kurtosis values range from very leptokurtic to platykurtic in nature. The sediments of pre-monsoon profiles show a range of variation in the Mean phi size from max (1.6440) to min (3.0570) i.e. ranging from medium to very fine sand and are moderately sorted to well sorted nature. Skewness values range from coarse skewed to fine skewed and Kurtosis values range from leptokurtic to platykurtic in nature. The foreshore slope of this sector is gentle when compared to other three sectors.

4.2. CM Diagram

The grain size parameters and plots of CM patterns are used to distinguish between sediments of different environments (Passega 1964, Visher 1969). In the present study, an attempt has been made to identify the seasonal variation in mode of deposition of sediments along the Karnataka coast by using CM pattern, where parameters C (One percentile of the grain size distribution) and M (the Median) have been plotted with phi values of the C and M obtained from cumulative curves in microns. The relation between C and M is an effect of sorting by bottom turbulence. CM pattern is subdivided into five segments viz; rolling (NO), bottom suspension and rolling (OPQ), graded suspension no rolling (QR), uniform suspension (RS) and pelagic suspension (S) as shown in (Fig. 2). The sediment samples of Karnataka coast fall predominantly in the tractive current and beach environment (that is by interaction with wave action) for both the seasons (Fig. 2).

10000000 Post-monsoor lOOOOOOf = Pre-monsoo n

6 6

1000000 lOOQOtH

I 100000 3 i lOOOOt 1 a lit

I i

Í 10000 100m =

tfi ts g 1000 IS 2 « 5, S 1.1 ill jjJMe 1 RK s agic Ar-Tprr»T4i <0 m {g loot 2 [■■' a ftfF 1 .Tills 2-Pelag" rttfl Tarra/'p

5 100 4:| 1 TTTj 5 .Tractive Current .Beach 0 IOC 4 -r/ 4.Tractive Current 5.Beach

6.Beach Gravel 6.Beach Gravel

10 1 10 100 1000 10000 100000 lOOOOOO Median Size, In Microns It 1 IO 100 1000 10000 1000001000000 Median Size, In Microns

Fig. 2. CM diagram plot showing seasonal variation in energy conditions for Karnataka coast.

The Tractive current diagram has been plotted which is indicative of the post-monsoon samples of sector I predominantly fall in the rolling condition, while few samples fall in bottom suspension and rolling conditions. Sediments of pre-monsoon season show that some samples fall in graded suspension and no rolling condition indicative of comparatively low energy conditions at some locations (Fig. 3a). Samples of sector II predominantly fall in bottom suspension and rolling condition for post- monsoon as well as pre-monsoon seasons with slight increase in C parameter thus indicating increase in energy level of the depositional currents (Fig. 3b). Sector III shows change in energy condition and the samples fall in rolling condition indicating high energy condition for the post-monsoon season, while a complete contrast is seen for the pre-monsoon season as majority of samples fall in bottom suspension & rolling condition depicting a drop in energy level (Fig. 3c). Samples of sector IV fall in bottom suspension & rolling and graded suspension no rolling condition with little or no change for both the seasons thus indicating low energy condition (Fig. 3d).

Sector I

post-mosoon pre-mosoon

1uuui £ looi — ___ luuut s loot == - = = = = :

e 1 -

p/ j iv pi" ■

i w s 1« =; M e: i 55 Tn s 101 1—e 7t

eee eeee: .jpc eeee:

it -- / iaii ■ii 1 .bottoni jllliil.n .pelagic su su s si i; mn& rolling ion no rollinç L 7 untforn 1 .pelagic s si k>nst rolling ion no rollim r

1 1 10 100 1000 median size, in microns it p 1 id 100 1000 median size, in microns

Sector III

post-monsoon p re-monsoon

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o / / Uniforrr SL on &. Rolling on No Rollin« o Uniforn 1 iei onS Rolling

/ Pelagic »

10 100 Median Size, In Microns 1000 10 100 Median Size, In Microns 1000

Sector IV

Fig. 3. (a - d): Tractive Current plots for the Karnataka coast.

4.3. Linear Discriminant Analysis (LDA)

The linear Discriminant function of Sahu (1964) has been used for multivariate analysis of beach sediments. According to Sahu, the statistical method of analysis of the sediments to interpret variations in the energy and fluidity factors seems to have excellent correlation with different processes and environment of deposition. The following formulae and their limitation to a particular environment were utilised to interpret the environment of deposition of sediments.

To distinguish environment of deposition between aeolian and beach, the following equation has been applied: Y1Aeol: Beach = -3.5688M+ 3.7016r2- 2.0766SK+ 3.1135KG (1)

Where if Y is > -2.7411, environment of deposition is beach, and if Y is < -2.7411, environment of deposition is aeolian.

To delineate and to confirm the environment of deposition between beach and shallow marine, the following equation has been applied: Y2 Beach: Shallow manne = 15.6534M+ 65.7091r2+ 18.1071SK + 18.5043KG (2) Where if Y is > 63.3650, environment of deposition is shallow marine, and if Y is <63.3650, environment of deposition is beach.

To distinguish environment of deposition between shallow marine and fluvial, the following equation has been applied:

Y3 Shallow marine: Fluvial= 0.2852M- 8.7604r2- 4.8932SK+ 0.0428KG (3) Where if Y is >-7.4190, environment of deposition is shallow marine, and if Y is <-7.4190, environment of deposition is fluvial.

(M= mean, r = standard deviation, SK= skewness and KG= kurtosis)

After calculating the above mentioned statistical parameters for all the samples using the equations given above, it is observed that 100% of the samples used to calculate Y3 for both the seasons, fall in the shallow marine condition. As far as Y2 is concerned, ~ 88% of the samples belong to shallow marine and ~12 % belong to beach environment for the post-monsoon samples, while pre-monsoon samples show distinct increase in shallow marine environment accounting 94% of the samples and only 6% of them belonging to beach environment. While for Y1, the samples show sector-wise as well as season-wise changes. Sectors I and III are predominantly beach environment and sectors II and IV are predominantly belong to a shallow agitated environment of deposition during post-monsoon. The pre-monsoon samples of sectors I and IV showing within range variations, while sector II has shown a predominant change with clustering of LDF plots is seen in beach environment of deposition. Sector III shows extreme change in energy condition as it changes from beach littoral to beach shallow environment of deposition. This change in energy condition can be very well correlated with tractive current plots. Sector IV shows little or no change in the energy conditions and clustering of plots is seen in shallow agitated environment (Fig. 4).

Aeolian/Shallow agitated

Aeolian Littoral Environment

post-monsoon

• Sector I

• Sector II ■ Sector III

• Sector IV

♦ •< S

Beach shallow ► Environment

_Stl__

Beach Littoral Environment

Shallow marine Beach

• Sector 1

♦ Sector II

■ Sector III

• Sector IV

Shallow marine Agitated

Fig. 4. (a ,b): Linear Discriminate Function (LDF) plotsfor the Karnataka coast.

5. Conclusion

The Karnataka coast studied for its beach sedimentary textural characteristics has been divided into four sectors from south to north where, the sectors I and III have coarser sediment with steeper foreshore slope while sectors II and IV show comparatively finer sediment with gentler foreshore slope. The significant difference in the foreshore slope in all these sectors can be correlated with the grain size distribution. Seasonal comparison of textural attributes of post-monsoon with pre-monsoon reveals more information thus enabling us to comment on the energy fluctuations and its effect on the sedimentation pattern along the coast. The CM diagram and the LDA reveal high energy environments at the time of deposition of sediments in sectors I and III and comparatively lower energy environment operated in sectors II and IV during post-monsoon season, while pre-monsoon season shows within range changes in these environments with slight increase in energy conditions in sector II and decrease in sector III. The increase in unimodality of the samples during pre-monsoon season is indicative of stabilization of the beaches throughout the coast.

Acknowledgement

The First two authorsare thankful to the Mangalore University for the award of fellowship under UGC SAP (DRS-I).The authors are thankful to Prof. C. Krishnaiah, Research Co-ordinator, OASTC for extending sieve analysis facilities and to Mr Athith Shetty for his immense support in the field as well as in the lab.

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