International Journal of Applied Environmental Sciences ISSN 0973-6077 Volume 14, Number 5 (2019), pp. 495-526 © Research India Publications http://www.ripublication.com

Studies on the Textural Characteristics of Sediments from Periyar River Basin, Kerala, Southern India

Arun T.J1, Krishna R Prasad1, Aneesh T.D1, Limisha A.T1, Sreeraj M.K1, Reji Srinivas1* 1Coastal Processes Group, National Centre for Earth Science Studies, Akkulam P.O, Thiruvananthapuram-695011, Kerala, India.

*Corresponding Author

Abstract The textural characteristics of sediments will provide valuable information to figure out the source of evolution under the river environment. The present work has been carried out to study the textural characteristics of river debris to understand the influence of sedimentary processes and the environmental factors on the distribution of grain size during the flood energy that interacts with the sediment transportation. The studies on textural characteristics clearly reveal that the sediments from the Periyar river basin were dominant in gravel and sand. The textural nomenclature of the sediments mostly shows in the order of gravelly sand - gravelly muddy sand - sandy gravel - slightly gravelly sand - muddy sandy gravel - slightly gravelly muddy sand and slightly gravelly sandy mud. The statistical parameters including the mean (Mz), standard deviation (σ1), skewness (Ski) and kurtosis (KG) sensitive to current energy changes which influences the dynamics of erosion, transportation and depositional velocity of the studied area establish that the entire river area is very coarse sand to very fine sand with very poorly sorted to moderately sorted nature. The debris was classified as coarse skewed to very fine skewed with platykurtic, mesokurtic and leptokurtic properties. The statistical parameters in the study area exhibit a little temporal as well as spatial variations. The lateral sediment inputs from the channel slope and the tributaries will influences strongly the variations in the textural characteristics in the bedload sediments towards the downstream direction within the study. The polymodal nature of sediments that confirming from the frequency distribution curves will support the observations. The unimodal and bimodal nature of the sediments were also present at certain locations of the study area. 496 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas

The hydrodynamic condition of deposition occurring in the region suggesting that the sediments are deposited under calm to a violent environment. The energy process discriminate functions of the sediments were deposited predominantly as the shallow agitated process under turbidity environment and remaining fluvial deltaic process. Based on the CM (Coarser one percentile value in microns) pattern, the river debris falls in the rolling and bottom suspension range. Keywords: Textural parameters, Periyar river basin, Frequency distribution curves, CM Pattern

INTRODUCTION The understanding of textural characteristics of sediment is relevant in sedimentological studies and it receives valuable attention in recent years. One of the most important natural properties of sediments and regularly used parameter for sediments are grain size analysis (Riyaz Ahmad Mir and Jeelani, 2015). The most fundamental natural properties of sediments that affecting their transport, entrainment as well the deposition is the distribution of grain size. The studies on the size of grains in the fluvial sediments will provide substantial information on the intrinsic properties within the sediments. The fundamental physical properties that controlling the hydraulics and the channel morphology of the stream will be exhibited by the sediments (Di Stefano and Ferro, 2002; Surian, 2002). The systematic studies on the granulometric analysis of fluvial sediments are able to provide an overview of the transportation histories as well as the depositional conditions (Blott, 2001; Mychielska-Dowgiallo, 2011). The rate of change in the size of sediment is closely related to the changes in the transportation of sediments and the flow resistance in the direction of downstream (Surian, 2002). The fining process towards the downstream is affected by the finer and coarser size fractions. Generally, the finer sediments are found in a low energy regime and the coarser sediments are clogged at a high energy environment (Bhattacharya et al., 2016). The most effective scavengers of chemical pollutants are the sediments that are enriched due to the transport of silt and clay particles as well as the erosion process (Rhoton et al., 2011). The physical transportation of sediments that including the sediment deposition and aggradations, tidal trapping and gravitational circulation will control the distribution of grain size (Wai et al., 2004). The resistance of flow will be influenced by the grain size of the sediment by altering the hydraulic characteristics near the bed of the channel (Jain et al., 2010). The distribution of grain size in sediments is considered as the normal sub-populations that representing the transportation of sediments by the process of saltation, rolling, and suspension (Inaman, 1952). The textural attributes of sediments are affected strongly by the considerable factors including the composition at the source area of adjacent lands, length, climate and energy that transporting the sediment and also the redox conditions near the environment of deposition (Fralick and Kronberg, 1997). The sandy silt and coarse-grained are the two types of texture that segregated by the fluvial sediments (Ramachandran, 2002). The sediment textural Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 497 attributes including the Mean (Mz), standard deviation (σ1), skewness (SK1), and kurtosis (KG) are widely used in reconstructing the environment of deposition of sediments and the sedimentary rocks (Komar 1998; Poppe and Elison, 2007). The depositional mechanism/processes of transport and the size parameters in sediments have a correlation between each other. Several studies in many ancient and modern sedimentary environments have established about these relationships (Itam et al., 2018; Chinna Durai et al., 2017; Temitope, 2016; Ganesh et al., 2013; Babu et al., 2007; Angusamy and Rajamanickam 2006). The knowledge of textural parameters and the sediment size is assumed to be one of the better tools to differentiate the various environments of depositional in recent as well as the ancient sediments (Kumar et al., 2010; Nordstorn, 1977). The Paleoclimate may also be interpreted from the analysis of grain size within sediments (Beal et al., 1956). Many attempts have been made by several sedimentologists to differentiate the sediments of various environments such as fluvial, fluviatile, and estuarine and other coastal environments over the years (Karuna Karudu et al., 2018; Mohtar et al., 2017; Bhattacharya et al., 2016; Manivel et al., 2016, Ramesh et al., 2015; Karuna Karudu and Jagannadha Rao, 2013).

MATERIALS AND METHODS The sediment samples that collected at each location of the study area using a stainless steel grab sampler were transferred into a pre-labeled airtight container. The sampling using grab will grant the collection of the sediments which including the sediments that transported through the bed and also the temporarily settled or trapped interstitially suspended materials among the bed load particles (Hajek, 2010). The samples were mixed thoroughly to make them homogeneous and a known quantity of samples was subjected to pre-treatment. The pre weighted samples were treated with dilute hydrochloric acid of 0.2N and hydrogen peroxide of 30% for removing the shell fragments as well as the organic matter, as they obstruct during the settling of the particles. The pretreated, samples were then washed and dried at ~50˚C for further analysis. Textural studies were carried out by standard sieving and pipette analysis techniques followed by (Carver 1971) and their statistical analysis following (Folk and Ward, 1957) was determined by using a modernized version of GRADISTAT software.

STUDY AREA The study area Periyar River Basin, (PRB) originating from the sivagiri hills on the southern Western Ghats (Figure 1). The Proterozoic high-grade Southern Granulite Terrain (SGT) of the Peninsular India that separated from the Archean low-grade Dharwar craton to the north by the orthopyroxene isograd advances the basin (Fermor, 1936). The Periyar River Basin that spreads in the districts including Idukki, Thrissur, and Ernakulam which falling within the central part of Kerala and lies between North latitudes 9°15’30” and 10°21’00”, East longitudes 76°08’38” and 77°24’32“. The river is having a 244 km of total length with a catchment area of 5398 498 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas km2 out of which, a total of 5284 km2 lies in the Kerala State and remaining in the Tamil Nadu State. From its origin, the river flows through an immense cliff of rocks in a north-westerly direction, before entering into the Arabian sea. Geologically, the crystalline rocks of Precambrian age are typically underlining the highland area of the basin, whereas the parts of lower-midland and the coastal land in the basin are covered by sedimentary deposits of Tertiary age. The crystallines are constituting of quartz-feldspar hypersthene granulites (charnockites), charnockite gneiss, hypersthene-diopside gneiss, hornblende gneiss, hornblende-biotite gneiss, quartz- mica gneiss, and pink granite.

Figure 1. Map of the Periyar River Basin showing the sampling locations

RESULT AND DISCUSSION Textural analysis in the sediments of the Periyar River was carried out to characterize the spatial variation in grain size characteristics qualitatively and statistically. The results are presented in (Table 1). Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 499

Table 1. Showing the textural characteristics of the sediments from Periyar River Basin

Sample no: Gravel % Sand % Mud % Sediment Type (Folk et al, 1970)

PR 01 44.86 53.80 1.34 sandy Gravel

PR 02 8.81 85.01 6.18 gravelly Sand

PR 03 3.35 87.60 9.05 slightly gravelly Sand

PR 04 7.79 88.29 3.91 gravelly Sand

PR 05 25.92 72.39 1.68 gravelly Sand

PR 06 6.61 88.72 4.67 gravelly Sand

PR 07 9.29 89.18 1.52 gravelly Sand

PR 08 30.15 66.76 3.09 sandy Gravel

PR 09 24.84 72.62 2.54 gravelly Sand

PR 10 1.41 89.49 9.10 slightly gravelly Sand

PR 11 32.03 60.94 7.03 muddy gravelly Sand

PR 12 27.18 68.02 4.80 gravelly Sand

PR 13 3.41 89.21 7.38 slightly gravelly Sand

PR 14 1.31 92.18 6.52 slightly gravelly Sand

PR 15 16.08 76.80 7.11 gravelly Sand

PR 16 17.56 77.72 4.72 gravelly Sand

PR 17 2.19 94.29 3.52 slightly gravelly Sand

PR 18 0.28 94.80 4.92 slightly gravelly Sand

PR 19 1.93 68.75 29.33 slightly gravelly muddy Sand

The sediment samples from the study area are substantially composed of gravel, sand, and mud. The overall distribution of grain size within the sediments is presented in (Figure 02). The proportion of gravel and sand in the sediments of the study area 500 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas shows (1% to 45% with an avg. 14%) and (54% to 96% with an avg. 80%) respectively with a mud percentage of (2% - 81%) with an avg. (19%) towards the downstream direction. The textural classification of sediments after Folk and Ward 1970 has been used to elucidate the textural nomenclature and results obtained are furnished in the (Figure 3). Based on the Folk and Ward classification, the study area exhibit a wide range in texture such as gravelly sand - gravelly muddy sand - sandy gravel - slightly gravelly sand - muddy sandy gravel - slightly gravelly muddy sand and slightly gravelly sandy mud. The channel gradient and the hard rock exposure within the channel of the river will influence the dominance of coarser particles in the sediments. So the changes in the granulometric composition of the river can be correlated to the local geology or the slope characteristics. The fining of sediments (sandy gravel to gravelly sand) are progressively abundant down the stream from the sample location (PR09), as the river enters into the midland and lowland region, where there is a change in physiography which in sequence are characterized by the fluctuating condition in the energy and also the variation in the granulometric composition. The abrasion and progressive sorting of sediments are the main reasons for a downstream decrease in phi mean and gradual enhancement of the fining of sediments (Riyaz and Jeelani, 2015; Allen 1970). Minor fluctuations in the sediment characteristics may be related to the changes in the river bed characteristics. Overall, the sediment samples exhibit a moderately immense value of sand during the time of the study. The innovative factors responsible for the noticed variation in the textural peculiarity of the riverine sediments are the conspicuous variation in the flow regimes. In addition to this, the construction of dams along the course of the river will also promulgate the drastic changes in the dispersal pattern of silt and clay in the sediment substratum.

Figure 2. Showing the grain size distribution of sediments collected from the Periyar River basin. Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 501

Figure 3. Showing the textural nomenclature after Folk and Ward (1970) of the Periyar river basin, based on sand silt clay ratios

The statistical parameters namely mean size, sorting, skewness, and kurtosis obtained from grain size analysis for the sediment samples of Periyar River were calculated and furnished in (Table 2). Table 2. A statistical overview of textural parameters of the sediments from Periyar River Basin

Sampl Mean Stan Skew Kurto Mean Size Stan Dev Skewness Kurtosis ID: Size Dev (KG) (SkI) (Mz) (σI) (SkI) (KG) (Mz) (σI)

PR 01 -0.340 1.096 0.545 0.753 Very Coarse Poorly Sorted Very Fine Platykurtic Sand Skewed

PR 02 0.747 1.607 0.134 1.816 Coarse Sand Poorly Sorted Fine Skewed Very Leptokurtic

PR 03 1.918 1.820 0.276 2.397 Medium Sand Poorly Sorted Fine Skewed Very Leptokurtic

PR 04 0.987 1.143 -0.156 1.510 Coarse Sand Poorly Sorted Coarse Skewed Very Leptokurtic

PR 05 0.294 1.334 0.007 0.722 Coarse Sand Poorly Sorted Symmetrical Platykurtic

PR 06 -0.042 0.978 0.567 5.832 Very Coarse Moderately Very Fine Extremely Sand Sorted Skewed Leptokurtic

PR 07 0.408 1.135 0.197 0.948 Coarse Sand Poorly Sorted Fine Skewed Mesokurtic

PR 08 -0.013 1.239 0.248 0.828 Very Coarse Poorly Sorted Fine Skewed Platykurtic Sand 502 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas

Sampl Mean Stan Skew Kurto Mean Size Stan Dev Skewness Kurtosis ID: Size Dev (KG) (SkI) (Mz) (σI) (SkI) (KG) (Mz) (σI)

PR 09 0.157 1.244 0.006 0.859 Coarse Sand Poorly Sorted Symmetrical Platykurtic

PR 10 2.029 1.598 0.487 2.271 Fine Sand Poorly Sorted Very Fine Very Leptokurtic Skewed

PR 11 0.395 1.816 0.121 1.086 Coarse Sand Poorly Sorted Fine Skewed Mesokurtic

PR 12 0.363 1.583 0.157 0.840 Coarse Sand Poorly Sorted Fine Skewed Platykurtic

PR 13 1.870 1.712 0.232 2.255 Medium Sand Poorly Sorted Fine Skewed Very Leptokurtic

PR 14 2.066 1.025 0.503 1.805 Fine Sand Poorly Sorted Very Fine Very Leptokurtic Skewed

PR 15 0.799 2.147 0.253 1.624 Coarse Sand Very Poorly Fine Skewed Very Leptokurtic Sorted

PR 16 0.200 1.336 0.155 1.200 Coarse Sand Poorly Sorted Fine Skewed Leptokurtic

PR 17 1.187 0.828 0.104 1.460 Medium Sand Moderately Fine Skewed Leptokurtic Sorted

PR 18 1.253 0.949 0.066 1.467 Medium Sand Moderately Symmetrical Leptokurtic Sorted

PR 19 3.275 3.321 0.643 1.018 Very Fine Sand Very Poorly Very Fine Mesokurtic Sorted Skewed

Mean Size (Mz) The graphic mean size will emulate the overall average size of the sediments in the grain size spectrum or the central tendency, that demonstrate the index of impacted energy to the sediment as a result of current velocity and turbulence of the medium of transport and also the energy circumstances of the environment of deposition (Chinna Durai et al., 2017; Itam et al., 2017; Sahu 1964). The graphic mean values in the surface sediments of the Periyar river ranges from (-0.340 to 3.275) with an average of (0.976), falling in the (very coarse sand to very fine sand) with the average displays course sand (Figure 4). The pattern of distribution in the mean size within the study area is revealing that the sediments were deposited under a moderately low energy condition and the low fluvial discharge. If the sediments become coarser then the phi mean size decreases and the phi mean size increases, then the sediment becomes finer due to the exponential transport mechanism that exists along with the river flow stated by (Ramesh, 2015; Anthony and Hequette, 2007). The coarser sediments in the sites will follow the impeachment under the little distance of transportation, moderate to high flow and also the presence of hard rock in the catchment area (Balamurugan et al., 2014; Eisma, 1981; Friedman and Sander, 1978). The fine sediments are eliminated by the strong winnowing action of the coarser particles in the high energy surroundings (Chinna Durai, 2017; Rieneck and Singh, 1980; Varathachari et al., 1968). The mean size within the sediments is exhibiting a trend, that decreasing towards the downstream direction and displays some fluctuations at certain locations. Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 503

The fluctuations are indicated by the changes in the hydrodynamic conditions that prevailing at the locations. Riyaz and Jeelani, 2015 suggested that the sediments that having coarser particles will be deposited and the finer will be transported further down towards the downstream direction as the competency of the river water slumps.

Figure 4. Spatial distribution of Mean size in the sediments of the Periyar River Basin

Standard Deviation (σI) The graphic standard deviation in sediments will indicate the degree of sorting or the uniformity in the distribution of particle size that describes the fluctuation in the aggressive energy either the acceleration conditions of the depositing agent and about its average velocity (Manivel et al., 2016). Spencer (1963) states that the standard deviation will reflect the energy condition of the depositional environment, without gauging the severity to which the sediment has been mixed. The higher value of standard deviation will exhibit the selection of grains that had taken place during the depositional as well as the transportation process. On the other hand, good sorting will represent the lower standard deviation values formed by the transport and deposits range of grain size due to the selective action of energy (Kamaruzzaman, 2002). The values of standard deviation within the Periyar river sediments range from (0.828 to 3.321) with the moderate value of (1.527) which indicating that the sediments are (moderately sorted to very poorly sorted) with the average was falling to the poorly sorted nature. In the study area, around 74% poorly sorted, 16% moderately sorted and 10% very poorly sorted (Figure 5). Like mean size, there is also a change in the values of standard deviation towards the downstream direction of the study area, that demonstrating the influence of mean grain size on the sediments sorting nature (Ramesh et al., 2015). The variability in the velocity of the depositing current as well 504 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas as the variation in the water turbulence will be attributed to the fluctuations in the sorting values (Rita et al., 2014). In general, the values of sorting are influenced by the continues involvement of coarser/finer sediments at varying proportions. So the decrease in the values sorting is mainly due to the transport of mixed sediments downstream. The distribution of sediments from the tributaries towards the river channel with high fluctuation in the velocity of flow and also the mass waste of consolidated soil materials during the rainy season due to the alteration of land will decline the sorting by the transport of mixed sediment downstream (Riyaz Ahmad Jeelani, 2015).

Figure 5. Spatial distribution of Standard Deviation in the sediments of the Periyar River Basin

Skewness (SkI) The skewness in sediments will measure the asymmetric degree of the frequency distribution of either predominant coarse or fine sediments with respect to the median (Xu et al, 2009). The variation in the energy conditions of the sedimentary process is reflected by the skewness (Jiang Siyi et al., 2014) and the skewness will be inversely proportional to the standard deviation (Cadigan, 1961). The amount of skewness in the Periyar river ranges from (-0.156 to 0.643) having an average of (0.240), declining of fine skewed (53%), very fine skewed (26%), Symmetrical (16%) and (5%) Coarse skewed nature respectively (Figure 6). The very finely skewed to finely skewed sediments generally imply the distribution of the grains from coarse to fine, then the rear end of the frequency curve will be at the finer end and whacks at the coarser end. If the sediments are coarse skewed, then the reverse condition will occur. The Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 505 sediments of Periyar Rivers are dominant in a very positively skewed nature. The unidirectional transportation, as well as the deposition of sediments at the low energy environments, is revealed by the positive skewness whereas the negatively skewed sediments, will illustrate the deposition at a high energy environment (Riyaz et al., 2015; Rajasekhara et al., 2008). The very fine skewed nature within the sediments will imply the enormous riverine input. The areas under high-intensity surroundings will develop the coarsely skewed sediments and the low energetic condition will flourish symmetrically skewed sediments. The variation in the values of skewness towards the downstream direction is also reflecting the changes in the flow pattern within the river (Riyaz and Jeelani, 2015).

Figure 7. Spatial distribution of Kurtosis in the sediments of the Periyar River Basin

Kurtosis (KG) The graphic kurtosis is the measure used to describe the departure from the normal distribution. The kurtosis is a measure of broadness or peakedness of the curve and it would be afflicted due to the irregularities near the distribution at the center (Cadigan, 1961). Kurtosis is inversely proportional as well as the important function of the standard deviation (Riyaz et al., 2015). The kurtosis values are a consensus for normal distribution and the greater kurtosis values will point out that 50 percent of the average velocity within the center is controlled by the fluctuation in the velocity. The kurtosis values in the sediments from the Periyar river ranges from (0.722 to 5.832) with moderate value (1.774) that revealing (platykurtic to extremely leptokurtic) with an average falling (very Leptokurtic) nature. The total samples show (26%) platykurtic (Central portion is better sorted than the tails), (58%) leptokurtic (tails better sorted than the central) and (16%) mesokurtic nature (Central and the tails have 506 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas uniform sorting) respectively (Figure 7). The variations in the velocity of the depositing medium are emulated in the kurtosis values. The greater fluctuations will imitate the higher value than unity (Verma and Prasad, 1981). The kurtosis values of the study area do not exhibit any particular trend in the downstream direction. The variation in the kurtosis value towards the downstream direction is a reflection of the flow peculiarity within the depositing medium (Baruah et al., 1997; Seralathan and Padmalal, 1994). The immaturity of the sand is imitated by the very platykurtic nature in the sediments, as a result of the uninterrupted addition of coarser/finer materials in the fluctuating proportion by the tributaries by the variation in the sorting values (Riyaz, 2015). The mesokurtic to leptokurtic nature within the sediments will be attributed to the unceasing admittance of well made or coarse grains after the scatter action along with with the equity in their original condition till the deposition (Avramidis et al., 2013).

Figure 7. Spatial distribution of Kurtosis in the sediments of the Periyar River Basin

Frequency Curves Frequency distribution curves (FDC) are the smooth curves that will represent the variation in the weight percentage of a different fraction within the sediments. The nature of the sediments can be illustrated through the FDC. The frequency distribution curves from the different locations of the study area are illustrated in (Figure 8). The distribution of frequency curves displays that the majority of the samples inferred the polymodal distribution. The studied sediments exhibit (74%) polymodal, (16%) bimodal and (10%) unimodal. The peak of an incremental frequency curve is served as the mode. The maximum concentration or the most frequently occurring particle size in a sample can be impersonated by mode. If a particle size of sediment is Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 507

PR 01 PR 02 PR 03 PR 04

PR 05 PR 06 PR 07 PR 08

Weight% PR 09 PR 10 PR 11 PR 12

PR 13 PR 14 PR 15 PR 16

PR 17 PR 18 PR 19 Phi Value

Figure 8. The Frequency distribution curves of the surface sediments in different locations (PR 01 - PR 19) of the Periyar River Basin domineering over the others in a sample, then it is termed as unimodal and the size- frequency curve can be characterized by more or less distinct peaks. Those curves are termed as bimodal that having two distinct peaks and polymodal are those which have more than two peaks. The polymodal nature of the curve is mainly due to the extreme fluctuations in the velocity at the depositing agent or the absence of a certain grain size in the size range of source material (Satyajit Sonowal and Jayanta Jivan Laskar, 2017; Sahu, 1964).

508 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas

Bivariate Plots The medium of transportation, energy condition and also the mode of deposition can be interpreted through the bivariate plots between certain parameters. (Visher, 1969; Folk and Ward, 1957) suggested that the interrelationship and trends displayed in the bivariate plots will demonstrate the depositional mode and its following environments.

(a) (b)

(c) (d)

(e) (f) Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 509

Figure 9. Binary plots between various textural parameters of the sediments of the Periyar River Basin. (a) Mean vs. Standard Deviation (b) Mean vs. Skewness (c) Mean vs. Kurtosis (d) Standard Deviation vs. Skewness (e) Standard Deviation vs. Kurtosis (f) Skewness vs. Kurtosis. (Index: VPS-very poorly sorted, PS-poorly sorted, MS, moderately sorted, MWS-moderately well sorted, WS-well sorted, VFS-very fine skewed, FS-fine skewed, NS-near symmetrical, VL-very leptokurtic, LK-leptokurtic, MK-mesokurtic, PK-platykurtic, VPK-very platykurtic) The geological significance of the parameters in grain size can be figured out through the bivariate plots (Sivasamandy and Ramesh, 2014). (Mason and Folk, 1958; Fredman,1961; Moiola and Weiser, 1968) used the bivariate plots between the values of graphic mean, graphic standard deviation, graphic skewness and also graphic kurtosis to differentiate the fields of river, beach and aeolian sediments. The interrelationship between the different size parameters can be exhibited in the bivariate plots (Sivasamandy and Ramesh, 2014). The bivariate plots of statistical parameters accomplished for Periyar sediments are portrayed in (Figure 9). The Mean size vs. Standard deviation is exhibited a linear relationship that the particles having the finer size (those particles having higher values of phi mean) displays enhanced sorting i.e. the sediment size decreases as the sorting worsens. The plot also showed the dominance of poorly sorted to very poorly sorted for a wide mean size. The sample shows the clustering of values to develop the broadened 'M' shaped established trend. This infers a stable and high energy flow during the deposition of these sediments. The Mean vs. Skewness indicates the decrease in grain size with positive skewed over negative skewed trend. The sediments of negative skewness ensure in a high energy environment and the positive skewness occurs under the low energy environments (Manivel et al., 2016). The plots between Mean and Kurtosis show a marginal rising linear pattern, that reflecting the combination of coarser and finer particles. The Standard Deviation vs. Skewness plot is showing that sediments are mostly coarse skewed to very fine skewed with very poorly sorted to moderately sorted behavior. This plot is generally used for the identification of a depositional environment following (Udhaba Dora, 2011). The plot of Standard Deviation vs. Kurtosis exhibits no distinct correlation amongst them. It shows that both statistical size parameters are independent of each other. The plot of Skewness vs Kurtosis indicates a positive correlation between them. The kurtosis increase and skewness also increase.

Suite Statistics Stewart, (1958) has proposed a plot of the discrimination field to understand the energy process by using the bivariate plot of mean and standard deviation (Figure 10). The sediments of the Periyar river were superimposed on the plot recommended by (Stewarts, 1958) and indicates that the majority of the sediments from Periyar were distributed in the field of river process except few in the inner shelf and quiet water environment. 510 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas

Figure 10. Energy Process based on Mean vs. Sorting (after Stewarts, 1958) for the sediment of the Periyar River Basin

Linear Discrimination Function The linear discrimination function analysis of the sediments was entrenched by Sahu to interpret the depositional setting by applying the following equations, where 'Mz' represents the mean grain size, 'ẟ1' represents the inclusive graphic standard deviation (sorting), 'Sk' represents the skewness and 'KG' represents the graphic kurtosis. a) Discrimination between Aeolian and Beach environment (Y1) 2 Y1 = -3.5688 Mz + 3.7016 ẟ1 - 2.0766 Sk + 3.1135 KG

If Y1 is ≥ -2.7411, the environment of deposition indicates Beach and Y1 is ≤ - 2.7411, then the environment of deposition implies Aeolian. b) Discrimination between the beach and the shallow agitated marine environment (Y2)

2 Y2 = 15.6534 Mz + 65.7091 ẟ1 + 18.1071Sk + 18.5043 KG

Here the Y2 ≥ 63.3650, the environment of deposition implies shallow agitated marine environment and Y2 is ≤ 63.3650, then the environment of deposition indicates the beach. c) Discrimination between shallow agitated marine and fluvial environment (Y3)

2 Y3 = 0.2852 Mz - 8.7604 ẟ1 - 4.8932 Sk + 0.0482 KG

If Y3 ≤ -7.4190, the environment of deposition indicates fluvial and Y3 ≥ -7.4190, the environment of deposition implies shallow marine.

Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 511 d) Discrimination between Fluvial and Turbidity (Y4)

2 Y4 = 0.7215 Mz - 0.403 ẟ1 - 6.7322 Sk + 5.2927 KG

If Y4 ≤ 10.000, the environment of deposition is fluvial and Y3 ≥ 10.000, the environment of deposition suggests turbidity. According to the linear discrimination function (LDF) analysis for the samples of Periyar (Table 3 and Figure 11), the values of Y1 falls in the Beach process. With reference to the values of Y2, the whole samples fall under a shallow agitating process. The Y3 values indicate the fluvial environment for the study area. The Y4 value shows that 68.42 % of Periyar river sediments are turbidity environment and the remaining 31.58 % are fluvial deltaic processes. So the result from the present study indicates that the depositions of the sediments in this area were derived from the fluvial environment (sediment discharged by the river).

Figure 11. Showing linear discrimination function (LDF) analysis in the sediments of the Periyar River Basin

512 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas

Table 3. Showing the linear discrimination function (LDF) analysis in the sediments of the Periyar River Basin

Sl No: Y1 Remarks-Y1 Y2 Remarks-Y2 Y3 Remarks-Y3 Y4 Remarks-Y4

PR 01 6.877 Beach 97.472 Sh. Agitated water -13.258 fluvial(deltaic) 6.926 turbidity

PR 02 12.270 Beach 217.380 Sh. Agitated water -22.974 fluvial(deltaic) 10.010 fluvial(deltaic)

PR 03 12.306 Beach 297.042 Sh. Agitated water -29.705 fluvial(deltaic) 14.596 fluvial(deltaic)

PR 04 6.337 Beach 126.419 Sh. Agitated water -10.329 fluvial(deltaic) 7.128 turbidity

PR 05 7.768 Beach 134.925 Sh. Agitated water -15.492 fluvial(deltaic) 3.361 turbidity

PR 06 20.674 Beach 180.420 Sh. Agitated water -10.890 fluvial(deltaic) 34.272 fluvial(deltaic)

PR 07 5.857 Beach 112.133 Sh. Agitated water -12.084 fluvial(deltaic) 6.118 turbidity

PR 08 7.797 Beach 120.546 Sh. Agitated water -14.633 fluvial(deltaic) 5.420 turbidity

PR 09 7.830 Beach 120.078 Sh. Agitated water -13.490 fluvial(deltaic) 4.077 turbidity

PR 10 8.267 Beach 250.301 Sh. Agitated water -24.051 fluvial(deltaic) 15.733 fluvial(deltaic)

PR 11 13.922 Beach 245.084 Sh. Agitated water -29.305 fluvial(deltaic) 5.521 turbidity

PR 12 10.273 Beach 188.720 Sh. Agitated water -22.575 fluvial(deltaic) 4.752 turbidity

PR 13 10.718 Beach 267.789 Sh. Agitated water -26.169 fluvial(deltaic) 13.667 fluvial(deltaic)

PR 14 1.091 Beach 143.890 Sh. Agitated water -10.992 fluvial(deltaic) 14.007 fluvial(deltaic)

PR 15 18.742 Beach 350.026 Sh. Agitated water -41.315 fluvial(deltaic) 9.017 turbidity

PR 16 9.306 Beach 145.338 Sh. Agitated water -16.268 fluvial(deltaic) 6.820 turbidity

PR 17 2.632 Beach 92.498 Sh. Agitated water -7.502 fluvial(deltaic) 9.006 turbidity

PR 18 3.289 Beach 107.116 Sh. Agitated water -7.782 fluvial(deltaic) 8.753 turbidity

PR 19 30.975 Beach 806.561 Sh. Agitated water -98.797 fluvial(deltaic) 7.638 turbidity

Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 513

Hydrodynamic Condition The sediments that laid down in different depositional environments, should have peculiar particle size distributions due to its differential erosion, transportation, and deposition (Lario et al., 2002). The hydrodynamic condition of deposition can be understood by using a ternary diagram proposed by Pejrup (1988) which mostly characteristics between an aggregated fine fraction and non-aggregated coarse fraction. The ternary diagram put forth by Pejrup (1988) has been applied in the sediments of the Periyar river to decipher the hydrodynamic dynamic condition of deposition that occurring in the region. The overall results show that the samples exhibit calm to violent environments (Figure 12).

Figure 12. Hydrodynamic deposition of the sediments (after Pejrup, 1988) for the Periyar River Basin

CM Pattern The cm pattern was introduced by Passega, 1957 to figure out the hydrodynamic forces that occupied at the time of impeachment of the granules. Passega, explained the distinct pattern of cm plots in terms of different modes during the transportation process by plotting the ' C ' i.e. coarser one percentile value grain size in microns and ' M ' median value in microns on log possibility scale. Visher (1969) elucidated the saltation, suspension, and surface creep or the rolling modes of transportation mechanism, by characterizing the log-normal subpopulations on the distribution curve of the total grain size. The CM pattern diagram perspectives an entire model of tractive current (the process of deposition) as illustrated by the (Passega, 1964), which is subdivided into several segments such as NO, OP, PQ, QR and RS displaying the different forms of debris convey. The segment NO represents the coarse grains transported by rolling, OP indicates the bottom suspension with rolling, PQ serves as 514 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas the graded suspension no rolling while the QR parallel to the line C=M represents the main channel deposits and the RS the uniform suspension. The CM plot for the Periyar sediments is shown in the (Figure 13). The result shows that most of the Periyar sediments fall in the NO region, which indicates the rolling field.

Figure 13. CM Pattern in the sediments of the Periyar River Basin

DISCUSSION The overall distribution of grain size in the study area exhibits a gradual downstream decreasing trend in the grain size. So the observed distribution of grain size is associated with the geological presumption of grain size that occurs in a tidal river during the downstream flow direction. The minimum current velocity required to move the sediments of a particular size is the critical erosion velocity that the sediments firm to motion, the movement stops at lowest transport velocity and deposited concede to the variation in the grain size with the heavier ones deposited first and more finer sediments come to rest as the current velocity decreases (Lawrence et al., 2015). So the relationship between the distribution of grain size and velocity of current that displayed in the study area can be described as the current velocity which is high upstream where the coarse grains remains and the decreased downstream towards the river mouth where the current energy is low. As the velocity increases in the upstream of the river channel, the more and more grains within the finer individuals on the spectrum of the particle are appropriated and will be selectively removed towards the downstream direction. This also agrees with the general rule after Chakrabarti (1974) for the mean grain size of sediments to decrease in the current flow direction. The hillslope process and the channel process will distribute the clastic sediments within the rivers. The gravity of the sediments is influenced by the hillslope processes and feasible to the river channel are through the overland flow, the various mass movement mechanism and the dissolution through the rain. The natural factors within the river channel such as terraces, bedrock outcrops, and tributaries that injecting Studies on the Textural Characteristics of Sediments from Periyar River Basin,… 515 materials those having the characteristics enact individually of processes will be negotiated longitudinally (Rice and Church, 1998). The materials that engender through these processes and the assign of sediments from upstream tributaries/channels will move through the river channel as a result of hydraulic conditions and velocity within the channel. The channel processes will control the deposition and transportation of the sediments (Pets and Forster, 1985). The higher percentage of sand within the freshwater region as compared to the river mouth can be explained by the process of abrupt rivers, which allows only the fine sediments to deposit first, but after reaching the river mouth this flow is declined dreadfully and allowing the very finer sediments to be deposited. In addition, the tides also play a major role in the transportation of offshore sediments onto the river mouth, thus the offshore materials that subsisting of mostly fine sediments would also be transported into the river but only little would reach further upstream due to the opposing river current (Kamaruzzaman, 2002). The subside in the velocities of the ebb-tidal currents as well as the occurrence of flocculation along with the impact of the flood tidal dominant current and the density current by salt wedges resulting in a wide distributional area having the very finer grain sediments (Fangjian et al., 2014). The velocities of the ebb-tidal currents that weakened quickly and the freshwater that mixed with the saltwater may also result in the accumulation of silt and clay in the areas of river mouth (Siyi et al., 2014; Pan et al., 2002). In addition, the rock exposures within the river channel, meanders, the anthropogenic interventions including the man-made structures including the check dams and the bridges in the fluvial system and the urbanized areas may also have a significant contribution to the changes in the overall dispersal pattern of sediments in the downstream of the rivers. The pronounced impressions of the longitudinal profile of the river channel could force a more expeditious decrease in the deposited material (Maria et al., 2008). Hence the minor fluctuations in the grain size population if any in the study area may also be attributed to these factors (Gohari et al., 2013, Wan Hanna, 2017).

CONCLUSION The present study was carried out to understand the nature of the distribution of grain size within the sediment samples collected at the Periyar river basin and suggested that the sediments are dominated by coarser particles. The various statistical parameters including the mean size, standard deviation, skewness, and kurtosis are evaluated in the sediments of the study area. The textural parameters exhibited that the sediments were very coarse sand to very fine sand, moderately sorted to Extremely poorly sorted with dominantly very positively skewed and platy kurtic to extremely leptokurtic nature showing texturally immature to sub matured debris of a fluvial surrounding. The fining of sediments in the downstream direction is attributed to the current velocity which is high upstream where the coarse grains remain and the decreased downstream towards the river mouth where the current energy is low and also due to change in physiography. Hence the variations of mean size within the 516 Arun T.J, Krishna R Prasad, Aneesh T.D, Limisha A.T, Sreeraj M.K, Reji Srinivas study area display the differential conditions of energy at different locations whereas, the variation in the values of sorting is indicated the continuous addition of finer to the coarser materials in varying proportions at different locations, particularly by the tributaries. The hydrodynamic condition of deposition clearly indicates that the sediments were deposited under the conditions of calm to a violent environment. Frequency distribution curves (FDC) drawn in the sediments of the study area clearly established that the sediments were dominantly made of polymodal in nature. The unimodal and bimodal nature of the sediments was also present at certain locations. From the energy process discriminate functions of the sediments were deposited predominantly as shallow agitated processes under turbidity environment and remaining fluvial deltaic process. The CM pattern diagram illustrates that the debris falls in the rolling with bottom suspension downward tractive current.

ACKNOWLEDGEMENT We would like to thank the Director, National Centre for Earth Science Studies (NCESS), Thiruvananthapuram, for his support and providing facilities to conduct this research.

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