A coastal plain is flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and a piedmont area.
The Coastal Plains of India lie on either side of the Deccan Plateau, along the western and eastern coasts of India. They extend for about 6,150 km from the Rann of Kutch in the west to West Bengal in the east.
The Indian coastline which is 7516.6 km long covers 6100 km of mainland coastline along with the Andaman, Nicobar, and the Lakshadweep islands.
The straight and regular coastline of India is the result of the faulting of the Gondwana land during the Cretaceous period.
The coastline of India touches 13 states andUnion Territories. The western coastal plains are along the Arabian Sea whereas the eastern coastal plains are located along the Bay of Bengal.
Coastal Plains of India are broadly divided into the Western Coastal Plains and the Eastern Coastal Plains.
Coastal Plains of India – West Coast
The west coast strip extends from the Gulf of Cambay (Gulf of Khambhat) in the north to Cape Comorin (Kanniyakumari).
The Western Coastal Plain is a narrow strip of land sandwiched between the Western Ghats and the Arabian Sea, ranging from 50 to 100 km (31 to 62 mi) in width.
It extends from Gujarat in the north and extends through Maharashtra, Goa, Karnataka, and Kerala.
West Coast, starting from north to south, it is divided into
(i) the Konkan coast,
(ii) the Karnataka coast and
(iii) the Kerala cost.
Mostly originating in the Western Ghats, the rivers are fast-flowing, usually perennial, and empty into estuaries. Major rivers flowing into the sea are the Tapti, Narmada, Mandovi and Zuari.
It is made up of alluvium brought down by the short streams originating from the Western Ghats.
It is dotted with a large number of coves (a very small bay), creeks (a narrow, sheltered waterway such as an inlet in a shoreline or channel in a marsh) and a few estuaries.
The estuaries, of the Narmada and the Tapi are the major ones.
The Kerala coast (Malabar Coast) has some lakes, lagoons and backwaters, the largest being the Vembanad Lake.
Vegetation is mostly deciduous, but the Malabar Coast moist forests constitute a unique ecoregion.
Western Coastal Plains of India
Rann of Kachchh in the north to Kanniyakumari in the South.
These are narrow plains with an average width of about 65 km.
Western coast plains are mainly divided into four categories
Kachchh and Kathiawar coast
Kutch and Kathiawar region
Kutch and Kathiawar, though an extension of Peninsular plateau (because Kathiawar is made of the Deccan Lava and there are tertiary rocks in the Kutch area), they are still treated as integral part of the Western Coastal Plains as they are now levelled down.
The Kutch Peninsula was an island surrounded by seas and lagoons. These seas and lagoons were later filled by sediment brought by the Indus River which used to flow through this area. Lack of rains in recent times has turned it into arid and semi-arid landscape.
Salt-soaked plain to the north of Kutch is the Great Rann. Its southern continuation, known as the Little Rann lies on the coast and south-east of Kachchh.
The Kathiawar Peninsula lies to the south of the Kachchh. The central part is a highland of Mandav Hills from which small streams radiate in all directions (Radial Drainage). Mt. Girnar (1,117 m) is the highest point and is of volcanic origin.
The Gir Range is located in the southern part of the Kathiawar peninsula. It is covered with dense forests and is famous as home of the Gir lion.
The Gujarat Plain lies east of Kachchh and Kathiawar and slopes towards the west and south west.
Formed by the rivers Narmada, Tapi, Mahi and Sabarmati, the plain includes the southern part of Gujarat and the coastal areas of the Gulf of Khambhat.
The eastern part of this plain is fertile enough to support agriculture, but the greater part near the coast is covered by windblown loess (heaps of sand).
The Konkan Plain south of the Gujarat plain extends from Daman to Goa (50 to 80 km wide).
It has some features of marine erosion including cliffs, shoals, reefs and islands in the Arabian Sea.
The Thane creek around Mumbai is an important embayment (a recess in a coastline forming a bay) which provides an excellent natural harbour.
Karnataka Coastal Plain
It extends from Goa to Mangalore.
It is a narrow plain with an average width of 30-50 km, the maximum being 70 km near Mangalore.
At some places the streams originating in the Western Ghats descend along steep slopes and make waterfalls.
The Sharavati while descending over such a steep slope makes an impressive waterfall known as Gersoppa (Jog) Falls which is 271 m high. [Angel falls (979 m) in Venezuela is the highest waterfall on earth. Tugela Falls (948 m) in Drakensberg mountains in South Africa is the second highest.]
Marine topography is quite marked on the coast.
Malabar Plain (Kerala Plain)
The Kerala Plain is also known as the Malabar Plain.
Between Mangalore and Kanniyakumari.
This is much wider than the Karnataka plain. It is a low-lying plain.
The existence of lakes, lagoons, backwaters, spits, etc. is a significant characteristic of the Kerala coast.
The backwaters, locally known as kayals are the shallow lagoons or inlets of the sea, lying parallel to the coastline.
The largest among these is the Vembanad Lake which is about 75 km long and 5-10 km wide and gives rise to a 55 km long spit.
Coastal Plains of India – East Coast
Lies between the Eastern Ghats and the Bay of Bengal.
It extends from the Ganga delta to Kanniyakumari.
It is marked by deltas of rivers like the Mahanadi, the Godavari, the Krishna, and the Cauvery.
Chilka lake and the Pulicat lake (lagoon) are the important geographical features of the east coast.
The temperature in the coastal regions often exceeds 30 °C (86 °F), and is coupled with high levels of humidity.
The region receives both the northeast monsoon and southwest monsoon rains. The southwest monsoon splits into two branches, the Bay of Bengal branch and the Arabian Sea branch.
The Bay of Bengal branch moves northwards crossing northeast India in early June.
The Arabian Sea branch moves northwards and discharges much of its rain on the windward side of Western Ghats.
Annual rainfall in this region averages between 1,000 and 3,000 mm (39 and 118 in). The width of the plains varies between 100 and 130 km (62 and 81 mi).
The plains are divided into six regions—the Mahanadi delta, the southern Andhra Pradesh plain, the Krishna-Godavari deltas, the Kanyakumari coast, the Coromandel Coast, and sandy coastal.
Eastern Coastal Plains of India
Extending from the Subarnarekha river along the West Bengal-Odisha border to Kanniyakumari.
A major part of the plains is formed as a result of the alluvial fillings of the littoral zone (relating to or on the shore of the sea or a lake) by the rivers Mahanadi, Godavari, Krishna and Cauvery comprising some of the largest deltas.
In contrast to the West Coastal Plains, these are extensive plains with an average width of 120 km.
This plain is known as the Northern Circarsbetween the Mahanadi and the Krishna rivers and Carnaticbetween the Krishna and the Cauvery rivers.
Eastern coast is divided into three categories-
The Utkal Plain comprises coastal areas of Odisha.
It includes the Mahanadi delta.
The most prominent physiographic feature of this plain is the Chilka Lake.
It is the biggest lake in the country and its area varies between 780 sq km in winter to 1,144 sq km in the monsoon months.
South of Chilka Lake, low hills dot the plain.
South of the Utkal Plain and extends upto Pulicat Lake. This lake has been barred by a long sand spit known as Sriharikota Island (ISRO launch facility).
The most significant feature of this plain is the delta formation by the rivers Godavari and Krishna.
The two deltas have merged with each other and formed a single physiographic unit.
The combined delta has advanced by about 35 km towards the sea during the recent years. This is clear from the present location of the Kolleru Lake which was once a lagoon at the shore but now lies far inland.
This part of the plain has a straight coast and badly lacks good harbours with the exception of Vishakhapatnam and Machilipatnam.
Tamil Nadu Plain
The Tamil Nadu Plain stretches for 675 km from Pulicat lake to Kanniyakumari along the coast of Tamil Nadu. Its average width is 100 km.
The most important feature of this plain is the Cauvery delta where the plain is 130 km wide.
The fertile soil and large scale irrigation facilities have made the Cauvery delta the granary of South India.