Physiographic ally the Indian coastal plains may be sub-divided into following three broad divisions: (a) Gujarat Coastal Plain, (b) West Coastal Plain, and (c) East Coastal Plain. ‘
(a) Gujarat Coastal Plain
Gujarat Coastal Plain (21° l’-24° 7’N and| 68°4′-74 4’E) occupies a total area of 1, 79,320 sq. km in Gujarat State (excluding Banaskantha and
Sabarkantha districts) and union territories of Daman, Diu and Dadra and Nagar Haveli. It is formed by the alluvial deposits of die Sabarmati, Mahi and numerous tiny parallel consequent streams whose process of formation is still continuing. Part of the plain is also die product of the depositional activity of the winds and recession of the sea.
The region consists of major and minor peninsulas, gulfs, islands, ranns, creeks, marshes, hills, plateaus etc. It contains Gondawana rocks (Umia series), resting over die marine Jurassic rocks and capped by Lower Cretaceous (Aptian) beds. The Deccan lava lies unconformably over the Umia series.
There appears simultaneous evidence of elevation and silting by die Peninsular Rivers in this region. Kadiiawar probably was linked with the mainland due to elevation and sedimentation. Relics of former channel-links exist in the form of marshes and lakes as also denial depression.
The eastern section of Gujarat Plain is a projected jet of Sindhu-Ganga alluvial tract in the Peninsular India. This projection is the outcome of an extensive Pleistocene sedimentation. Present rivers have further advanced this deposition to the Gulf of Cambay.
Among the highlands mention may be made of the Arasur mountains in eastern Gujarat, the Rajpipla hills (Satpura hills) famous for agate quarries, the Panieramountain in Bulsar district, Saliyadris in the southern side and the igneous complex of die Girnar Hills (Gorakhnatii peak 1117 m).
The Rann of Kachchh is ‘an extensive country of naked tidal mudflats transected by dead and live creeks. The whitish vertebrae of salts or ecums appear as white bonny structures in die dried creeks. Live creeks form dendritic pattern of drainage and there has been accentuation in this pattern due to eartiiquakes. South of the Rami lies Kachchh, formerly an island, this is almost surrounded by die Rann except in the south-west. Here Jurassic-Miocene sandstones capped widi basalts, rise to an elevation between 315-385 m (Pachcham Island in the nortii 534 m). On the outskirts of Kachchh, alluvial and aeolian deposits occur.
Physiographically the Gujarat plain may be divided into (i) die Rann, (ii) the Kachchh Peninsula, (iii) the Saurashtra Plain, and (iv) the Gujarat alluvial Plain.
(b) West Coastal Plain
West Coastal Plain (8° 15′-20° 22’N and 73° 40′-77° 30’E) between die Sahyadris and the Arabian Sea covers a total area of 64,264 sq. km (N-S length 1,400 km, E-W width 10-80 km). It has an elevation from sea level to 150 m, at places reaching more than 300 m. It is mainly characterised by sandy beaches, coastal sand dunes, mud flats, and lagoons, alluvial tracts along rivers, estuary, laterite platforms and residual hills.
The Sahyadris (elevation 760-1,220 m) run almost parallel and present their steep face to the low lands with Thalghat and B horghat gaps in the north and Palghat gap in the extreme south. The West Coastal Plain may be sub-divided into three main regions ;-(i) the Konkan, (ii) the Karnataka or Kanara, and (iii) die Kerala or Malabar. The Konkan Coastal Plain consisting of undulating lowlands is 530 km long and 30-50 km broad. It is widest near Mumbai, in ‘the amphitheatre-like basin of the Ulhas’ which has pushed the Sahyadris eastward away from the coast.
The North Konkan is characterised by sandy spits intruding into mudflats and wider creeks close to the sea and by low coastal ranges separated by longitudinal valleys away from the coast.
The South Konkan, in contrast, is a rocky and rugged country. Here lofty hills and elevated plateaus, intersected by numerous creeks and navigable streams, are found close to the coast. The coast along Goa is more deltaic and is of ria type characterised by wide estuaries.
The Karnataka Coastal Plain (525 km long and 8-24 km wide) depicts three parallel belts of landforms : (i) behind the coast lies a narrow belt of very recent deposits, forming sand dunes, lagunar or estuarine mudflats or marshes and valley plains (elevation 30 m), (ii) an erosion platform (width 25 km, height 61 m) well dissected by steepsided valleys and containing lateritic deposits of Pliocene age, (iii) inland belt of isolated hills of Archaean gneisses (91-305 m).
The Malabar Coast is 550 km long and 20-100 km wide. It is narrower in the north and south and wider in the middle section. Maximum extension is found in the valleys of the Beypore, the Ponnani (draining dirough Palghat gap), and the Periyar and Pamba-Achankovil rivers.
It also has belted arrangement of landforms. Sand dunes (locally known
as Teris) arc very common which have helped to form a number of shallow lagoons and backwaters (Kayals) along the coast. These lagoons are linked together to facilitate navigation through small country-boats. Here Ashtamudi and Vembanad lakes are important. The coast shows evidence of emergence.
(c) East Coastal Plain
The East Coastal Plains (8°-22° 13′ 30″ N and 77° 30′ 30″-87°20′ E) cover about 1,02,882 sq. km of area along the coasts of Orissa, Andhra Pradesh and Tamil Nadu. It lies between the Eastern Ghats and the Bay of Bengal and is more extensive and wide than its western counterpart.
These plains are formed by the alluvial fillings of the littoral zone comprising some of the largest deltas of the world. These plains extend from Kanniyakumari northwards to the Kaveri, Krishna and Godavari deltas for 1,100 km with an average width of 120 km. Further northward, they almost approach the sea but widen again north of Berhampur and extend to the Chilka lake, the Mahanadi delta, and the Balasore coastal plain, where they merge into the deltaic plains of the Ganga.
The East Coastal Plains mainly consist of Recent and Tertiary alluviums. These are monotonous plains rising gently westward to the foot of the Eastern Ghats. The monotony of the topography is broken by the presence of numerous hills, especially between the Adyar and Palar rivers in Tamil Nadu.
The region has a straight shoreline with well defined beaches of sand and shingles. The most famous beach is the Marina Beach in Chennai. All along the coast there are several sandbars generally athwart the river mouths. Between the mainland and the Gulf of Mannar and the Palk Strait there are tiny coral islands which form flourishing fishing centres. Further inland there is a zone of sand dunes caused mainly by the action of wind at low-water tide.
Adjoining the line of sand dunes all along the coast are found lagoons formed recently in association with coastal uplift. The Chilka Lake in the south-west of the Mahanadi delta is the biggest lake (65 km x 8 km) of country (area 780 to 1,144 sq km from winter to monsoon months).
The Pulicat lake lies further southward on the border of Andhra and Tamil Nadu coastal plains. The lake, 80 km long N-S and 3-18 km across, comprises several small islands within it.
Further south are other backwater lakes like Ennore and Mahabalipuram. The backwaters have also led to the formation of Marakaran, Veakaranyam and Mangreni swamps in Orissa and Andhra coasts. The Samang and Sur located north and north-east of Puri are sweet water lakes. Thus, in general, three types of shorelines have been developed along the East Coastal Plains: (a) the rocky shorelines between the deltas (Ganjam and Vishakhapatnam coast), (b) the sandy shorelines upon the Tertiary gravels, and (c) the alluvial and silty deltaic shorelines at the mouths of the Mahanadi, Godavari, Krishna and Kaveri rivers.
The East Coastal Plains may be divided into three smaller physiographic units: (i) Tamil Nadu Plains, (ii) Andhra Plains, and (iii) Utkal Plains. Tamil Nadu Plains stretch to about 675 km with an average width of 100 km between Cape Camorin and Pulicat Lake. Here Kaveri delta and Pulicat lagoon (separated from the sea by Sriharikota Island) are prominent features. The Andhra Plains lie between Berhampur and Pulicat Lake and have been formed by the deltas of the Krishna and Godavari rivers. Kolleru lake situated between these two deltas marks the coastline of the past indicating the seaward advance of the plains. The plains extend up to about 199 km inland along the Krishna and maintain almost same width up to Chennai.
The Utkal Coastal plains include the Mahanadi delta and extend for about 400 km. Here the coastline is smooth and is fringed with sand dunes. It shows signs of emergence. The plain is broad (100 km) in front of the mouth of Mahanadi.