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Lower Vellar, Cuddalore District, Tamil Nadu
Background Information
The area experiences a tropical humid climate influenced by the nearby Bay of Bengal. It receives an average annual rainfall of 1400 mm, both during southwest and northeast monsoons. The highest precipitation months are September to December, during the northeast monsoon.
The temperature is warm during the summer months with a maximum temperature of 41° C in May. The lowest temperatures range between 18° C and 21° C in winter months.
Relative humidity is at a maximum around 90% and at a minimum between 28 to 45%.
The area is drained by Paravanar and Uppanar rivers. Small nalas viz. Sengal Odai and Kaniyakoil Odai, also drain the area and join the Paravanar river. Perumal eri is the major water body existing within the area. It covers an area of 15 sq km and receives water from Paravanar and many small streams. During monsoon, the Perumal eri fills up and drains to the Uppanar river. The small nallas oriented along the northwest-southeast direction form the catchment of Perumal Eri.
The area is a gently sloping terrain characterized by alluvial plains, flood plains and coastal plains. Flood plains, including scattered sand bars, are developed along the river course and alluvial plains are well developed along the mouth of the river. The major geomorphic features along the coastal tract are coastal plains. The coastal plain is extensive in the south-eastern part and narrows down towards the north-eastern side. The coastal plains exhibit specific geomorphic features which include strand lines (paleo coast line) beach ridges, dune complex, sand dunes, mud flat, salt flat and salt pan. Backwater is observed in the northern part of the area.
The landforms play a crucial role in the recharge process and formation of shallow aquifer system especially in the coastal plain. The drainage anomaly of the river on the southern boundary indicates the possibility of significant changes in the underlying lithology / geological structure.
Figure 6.3: Satellite imagery showing historical coast lines, sand dunes and drainage anomaly
Source: Satellite data from the website of Department of Space, interpreted by J. Kumar
Red soil and river alluvium are the major soil types observed in the area.
Land use
Geologically, the Lower Vellar Sub Basin area presents three distinct formations:
Recent deposits, comprising soils, blown sands, kankar, laterites and lateritic gravel, and river alluvium. The alluvia of Manimuktha Nadhi and Vellar Rivers are mostly sands and sandy clays. Laterities and lateritic gravels overlie a large part of the area.
Tertiary formations, including:
Cuddalore Sandstone of Mio-Pliocene Age, comprising argillaceous sandstone, pebble bearing sandstone, ferruginous sandstone, grits and clay beds. Sandstones of the Cuddalore formation are whitish, pinkish, reddish or mottled in colour and are chiefly argillaceous in nature. Lignite deposits occur in these formations.
Gopurapuram formations, which are essentially argillaceous, comprising silts, clay stones, calcareous sandstones, siliceous limestones and algal limestones.
Upper Cretaceous calcareous Sandstones, fine to coarse grained, and limestones.
These are underlain by Archaean crystallines, occurring at shallow depth in the western part and dipping towards the coast in east and southeast directions. Thus, the eastern part holds a very thick sedimentary sequence of Cretaceous, Tertiary and Quaternary formations resting over the crystalline basement.
The geological succession is as follows:
Era Age Formation Lithology
Quaternary Recent to subrecent Alluvium and Laterite Alluvium, Coastal Sands, clays and Laterite
Tertiary Mio-Pliocene Cuddalore Sandstone Argilaceous sandstone, clays (variegated), with lignite seams and pebble beds
  Eocene Sandstone Black clays or shales, grey coloured sandstones, lignite, calcareous sandstones and shales and siliceous limestones with fossils
Mesozoic Cretaceous Ariyalur Limestone Shell and Siliceous Limestones, marls, etc.