Sedimentological Studies of Nagavali-Vamsadhra Estuaries, East Coast of India, Andhra Pradesh

Abstract

The importance of textural characteristics of estuarine sediments in the present study is useful in understanding the intensity of sediment transportation in the fluvial systems. The importance of grain size parameters of the sediments is well recognized in sedimentology and has been well established. The present study illustrates the detailed textural characterization of Nagavali and Vamsadhara estuarine sediments of East Coast of India, Srikakulam, Tamil Nadu. The textural studies reflect that the sediments have significant fractions of fine to medium sand, silt and clay, where fine sand is predominant in both the estuaries. The statistical sedimentary analysis for the samples says mean size, standard deviation, skewness and kurtosis is carried out. The sediment is dominantly fine sand with moderately sorted, nearly skewed in Nagavali estuary whereas the sand is very well sorted and nearly symmetrical in Vamsadhara estuarine sediments. The sediments of both are similar in size and show low variance. The present study suggesting that the sediments deposited in low energy conditions. The Nagavali estuary samples shows nearly symmetrical skewness and the Vamsadhara estuary samples shows nearly symmetrical to positive skewness. Negative Skewness was being correlated with high energy and winnowing action and positive Skewness with lower energy levels. The present study demarcates the sedimentation have no influence of nearshore tidal activity.

Introduction

This study examines the textural characteristics and grain-size parameters of estuarine sediments from the Nagavali and Vamsadhara river systems to understand sediment transport intensity and depositional environments. Grain-size analysis is a well-established tool in sedimentology and is widely used to interpret both ancient and modern depositional settings such as rivers, beaches, and dunes.

The study area lies along the Bay of Bengal coast in Srikakulam District, Andhra Pradesh, where both rivers originate from the Eastern Ghats and flow southeastward to form estuaries. Geologically, the region is dominated by Archean rocks of the Eastern Ghats Supergroup, with widespread alluvial deposits over granite gneisses, creating a largely flat, agriculturally productive plain.

A total of 30 sediment samples (15 from each estuary) were collected using PVC tubes and grab samplers. After chemical treatment and drying, samples were subjected to sieve analysis, and statistical parameters such as mean size, standard deviation (sorting), skewness, and kurtosis were calculated following Folk and Ward’s method.

Results show that sediments in both estuaries are dominated by sand, with minor silt and clay.

• Nagavali estuary sediments range from medium to fine sand, are generally moderately sorted, mostly nearly symmetrical to slightly skewed, and show platy-, meso-, and leptokurtic distributions, indicating variable energy conditions.

• Vamsadhara estuary sediments also range from medium to fine sand but are very well sorted, mostly nearly symmetrical, and display platykurtic to very leptokurtic characteristics, suggesting more uniform and stable depositional conditions.

Scatter plot analysis of statistical parameters reveals interrelationships that help infer transport mechanisms and depositional environments, supporting earlier studies that grain-size trends can distinguish between fluvial and estuarine settings.

Conclusion

From grain size distribution studies of Nagavali and Vamsadhara Estuarine systems it is shown that most of the sediments are medium to fine sand and silts. The sediment deposition has taken place during the slow river discharge. Bivariant plots such as standard deviation vs mean, skewness vs mean, standard deviation vs skewness presents the following comparative statistics between the two estuaries. Comparison of the Nagavali and Vamsadhara River Estuaries: 1) The graphic mean size value depicts the average particle size or a measure of central tendency. The mean size of the both estuaries having the medium sand to fine sandy nature. The avg. value of the estuaries is 2.23 ? and 2.05 ?. The average value shows the dominance of medium sand (MS) size sediments and the rest very smaller amounts of silt. The variations in ? mean size reveals the differential energy conditions leads to their deposition of such sediments in different locations. 2) Standard deviation is a measure of the dispersion of the grain size distribution. It is an important parameter in sediment analysis because it reflects the energy condition of depositional environment. The Nagavali estuary sediments shows moderately sorted nature and Vamsadhara estuary sediments have Very well sorted nature. The present study suggesting that the sediments deposited in low energy conditions. The variations in the sorting values are likely due to continuous addition of finer/coarser materials in varying proportions. 3) The graphic Skewness is the measure of symmetrical distribution, i.e. predominance of coarse or fine sediments. The Nagavali estuary samples shows nearly symmetrical skewness and the Vamsadhara estuary samples shows nearly symmetrical to positive skewness. Negative Skewness was being correlated with high energy and winnowing action and positive Skewness with lower energy levels. 4) Variations in the kurtosis values are a reflection of the flow characteristics of the depositing medium, the dominance of finer size of platy kurtic nature of sediments.

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