The Coastal Plains: a submerged west and an emergent east

Detail

1. What the coastal plains are

• The coastal plains of India are two strips of low, flat land. They lie between the edge of the Peninsular plateau and the sea.
• Western coastal plain: between the Western Ghats and the Arabian Sea.

• Eastern coastal plain: between the Eastern Ghats and the Bay of Bengal.

• The two plains were shaped by opposite processes. In the west the land sank. In the east the land rose.

• Submerged coast: a coast where the land has sunk, or the sea has risen, so the sea floods the lower parts of the land. River mouths and valleys get "drowned".

• Emergent coast: a coast where the land has risen, or the sea has fallen, so the old sea floor now shows as flat, sandy land.

• Length of India's coastline (revised): 11,098.81 km, re-measured by the National Hydrographic Office (NHO) with the Survey of India [2][3].

• The old figure was 7,516.6 km. The Ministry of Home Affairs had used it since the 1970s [2][3].
• Why the new figure is longer: the 1970s figure was measured on small-scale maps (1:4,500,000 or smaller). The new one used larger-scale maps (1:250,000), measured along the High-Water Line with 2011 base data. A more detailed map picks up more bends in the coast, so the length goes up [2][3].
• The Ministry of Ports, Shipping and Waterways notified the revised length by a circular dated 29 April 2025 [2].

2. West vs east: a quick comparison

Feature	Western coastal plain	Eastern coastal plain
Type of coast	Submerged (land sank)	Emergent (land rose)
Width	Narrow; narrowest in the middle, broader in the north and south	Broad
Sea	Arabian Sea	Bay of Bengal
River mouths	Estuaries (Narmada, Tapi); no deltas	Large deltas (Mahanadi, Godavari, Krishna, Kaveri)
Harbours	Many natural harbours on a drowned, deep coast	Fewer good harbours; NCERT says the continental shelf runs up to 500 km out
Typical water bodies	Kayals (backwaters), creeks, coves	Large lagoons: Chilika, Pulicat
Main rain	South-west monsoon (June–September), very heavy	Coromandel: north-east monsoon and cyclones (October–December)
Parts (north → south)	Kachchh-Kathiawar → Konkan → Goan → Malabar	Utkal plain → Northern Circars → Coromandel

3. Western coastal plain: a submerged coast

• Proof of sinking: the ancient city of Dwaraka (Gujarat, on the Kathiawar peninsula) is believed to have been on the mainland. Today it is believed to lie under the Arabian Sea.
• Shape: a narrow belt. It is narrow in the middle (Konkan–Goa) and broader in the north (Gujarat) and south (Kerala).
• Parts, from north to south:

Part	State(s)	Key features
Kachchh and Kathiawar coast	Gujarat	Broadest northern part; site of drowned Dwaraka; Kandla (Deendayal) port
Konkan coast	Maharashtra (Daman to Goa)	Narrow, rocky, cut by creeks; very heavy rain
Goan coast	Goa	Marmagao (Mormugao) port
Malabar coast	Kerala and coastal Karnataka	Kayals (backwaters), coconut, spices; very heavy rain

Why the drowned coast gives good ports

• The land sank → the sea flooded the river valleys and low ground → deep, sheltered inlets formed close to the shore → ships can come near the land.
• So the west coast has many natural harbours:
• Kandla, renamed Deendayal Port from 25 September 2017 after Pandit Deendayal Upadhyay [7].
• Mazagaon (Mumbai).
• Jawaharlal Nehru Port (Nhava Sheva), near Mumbai.
• Marmagao (Mormugao), Goa.
• Mangaluru (New Mangalore), Karnataka.
• Kochi (Cochin), Kerala.

Why the west coast has no deltas

• A delta is a fan-shaped piece of land made of silt. It forms where a river drops its load at the mouth faster than the sea can carry it away.
• The west coast has no deltas for three reasons:
• Short, swift rivers: the rivers fall fast from the Western Ghats down a steep slope. They do not get time to drop their silt on the plain.
• Sinking coast: the land went down, so river mouths were drowned. They became estuaries instead of deltas.

• Estuary: a wide, funnel-shaped river mouth where fresh river water mixes with salt sea water and the tide moves in and out. Examples: the Narmada and the Tapi, which both flow west into the Gulf of Khambhat (Arabian Sea).

• The coast is also full of coves (small, curved bays), creeks (narrow inlets of the sea) and estuaries (Class 7 NCERT).

4. Konkan coast

• Location: Maharashtra, from Daman to Goa.
• Character: narrow, rocky and cut by many creeks. It gets very heavy rain.

• Why so rainy: the moist south-west monsoon winds hit the Western Ghats → the air is pushed up → it cools and its water vapour condenses → heavy rain falls on the coast and the side of the hills facing the wind (the windward side).

• Konkan Railway:

• Formed as a company in 1990 to build a rail link from Roha (near Mumbai) to Thokur (near Mangaluru) [6].
• The whole line opened for traffic on 26 January 1998 [6].
• It runs 741 km through Maharashtra, Goa and Karnataka, along the coast and the Western Ghats. It has 84 km of tunnels [6].
• The rocky, creek-cut coast and the steep Ghats made this one of India's hardest railway projects.

5. Malabar coast and the Kerala backwaters

• Location: Kerala and coastal Karnataka, the southern, broader end of the west coast.
• Character: famous for kayals, coconut, spices and very heavy rain. The south-west monsoon reaches here first.
• Kayal (backwater): a shallow lagoon or lake near the sea. It is cut off from the sea by a sand bar, a long ridge of sand built up by waves and currents.
• How they form: waves and currents pile sand into bars along the shore → the bars close off shallow bays and river mouths → calm, shallow water bodies form behind them → these become the Kerala backwaters.

• Uses: fishing, inland navigation (boats and houseboats) and tourism.

• Vembanad is the largest kayal.

• It is part of the Vembanad-Kol Wetland, a Ramsar site since 19 August 2002, covering 151,250 ha [5].
• It is fed by 10 rivers and is the largest brackish (partly salty), humid tropical wetland on India's south-west coast [5].

• It is known for its clams and supports the third-largest waterfowl population in India in winter [5].

• Nehru Trophy Vallamkali: a boat race of long "snake boats". It is held every year on Punnamada Kayal, which is part of Vembanad lake, near Alappuzha (Kerala).

6. Eastern coastal plain: an emergent coast

• Shape: broad. It is much wider than the western plain.
• Why it is broad and has deltas:
• The land rose, so a wide strip of former sea floor now forms flat land.
• The big Peninsular rivers flow east over a gentle slope. They are long and carry a lot of silt.

• The silt builds large deltas: from north to south, the Mahanadi (Odisha), Godavari and Krishna (Andhra Pradesh) and Kaveri (Tamil Nadu).

• Fewer ports: NCERT says the continental shelf extends up to 500 km into the sea.

• Continental shelf: the shallow, gently sloping sea floor at the edge of a continent, before the deep ocean begins.

• A wide, shallow shelf with silt from the deltas → shallow water near the coast → large ships cannot come close → good ports are hard to build and keep dredged.

• Regional names (north to south):

• Utkal plain: Odisha.
• Northern Circars: Andhra Pradesh.

• Coromandel coast: Tamil Nadu.

• Lagoons: a lagoon is a body of shallow water cut off from the sea by a natural barrier such as a sand bar, spit or reef.

• Chilika (Odisha): India's largest brackish-water lake. It is cut off from the Bay of Bengal by a long sandy ridge, and sea water still flows in and out, so its salt level changes a lot with the seasons [4]. It became a Ramsar site on 1 October 1981, with an area of 116,500 ha [4].
• Pulicat: on the Andhra Pradesh–Tamil Nadu border, north of Chennai.

East-coast ports (north to south)

Port	State	Note
Kolkata-Haldia	West Bengal	River port on the Hugli; Kolkata Port Trust renamed Syama Prasad Mookerjee Port (Cabinet approval, 2020) [9]
Paradip	Odisha	Near the Mahanadi delta
Visakhapatnam	Andhra Pradesh	Deep, naturally sheltered harbour
Chennai	Tamil Nadu	Artificial harbour
Ennore → Kamarajar Port	Tamil Nadu	Renamed after K. Kamarajar, former Chief Minister of Tamil Nadu [10]
Tuticorin → V.O. Chidambaranar Port	Tamil Nadu	Renamed in 2011 [10]

• Major Ports (12): Chennai, Cochin, Deendayal (Kandla), Jawaharlal Nehru (Nhava Sheva), Kolkata, Mormugao, Mumbai, New Mangalore, Paradip, V.O. Chidambaranar (Tuticorin), Visakhapatnam and Kamarajar [8].
• Six are on the west coast and six on the east coast. Even with fewer natural harbours, the east coast has as many Major Ports, because most of them are artificial or river ports.

7. Coromandel coast

• Location: Tamil Nadu.
• Character: low and sandy, with the Kaveri delta and lagoons.
• Rain pattern (a common exam trap):
• June–September (south-west monsoon): Coromandel stays fairly dry. It lies in the rain-shadow (the dry side of a mountain, away from the wind) of the Western Ghats, and the south-west winds blow parallel to this coast.

• October–December: the north-east monsoon (the retreating monsoon) picks up moisture over the Bay of Bengal → it reaches the Tamil Nadu coast → it brings most of the year's rain. Cyclones from the Bay of Bengal add heavy rain in the same months.

• 2004 Indian Ocean tsunami: it struck the Coromandel coast and the Andaman and Nicobar Islands.

• Tsunami: a series of very long, high sea waves caused by an undersea earthquake, landslide or volcano.
• The low, flat, sandy Coromandel coast let the waves reach far inland, which caused heavy damage.

Prelims Hooks

• Parts of the west coast, north → south: Kachchh-Kathiawar → Konkan → Goan → Malabar. East coast, north → south: Utkal → Northern Circars → Coromandel.
• West = submerged (drowned Dwaraka, estuaries, natural harbours); East = emergent (broad plain, deltas, fewer good ports). Watch for questions that swap the two.
• Narmada and Tapi form estuaries, not deltas. The Mahanadi, Godavari, Krishna and Kaveri form deltas.
• India's coastline: 11,098.81 km (revised; notified 29 April 2025), up from 7,516.6 km. The change comes from a more detailed map scale, not from new land [2][3].
• Vembanad is the largest kayal. The Nehru Trophy Vallamkali is held on Punnamada Kayal (Kerala). Vembanad-Kol became a Ramsar site in 2002 [5].
• Chilika (Odisha) is India's largest brackish-water lake and was one of India's first Ramsar sites (1981) [4]. Pulicat lies on the Andhra Pradesh–Tamil Nadu border.
• Renamed ports: Kandla → Deendayal (2017) [7]; Tuticorin → V.O. Chidambaranar (2011); Ennore → Kamarajar [10]; Kolkata → Syama Prasad Mookerjee [9].
• Konkan Railway: Roha–Thokur, 741 km, opened 26 January 1998, runs through Maharashtra, Goa and Karnataka [6].
• Trap: the Coromandel coast gets most of its rain in October–December (north-east monsoon), not in June–September.
• Trap: the Northern Circars are in Andhra Pradesh, not Odisha. Odisha's coastal plain is the Utkal plain.

Mains Points

• How coast type shapes the economy:
• A submerged west coast → deep, sheltered inlets → natural harbours (Mumbai, JNPT, Mormugao, Kochi) → port-based industry and trade with West Asia and Europe.

• An emergent east coast → broad deltas → fertile soil, dense population and rice farming (the Godavari, Krishna and Kaveri deltas are major rice bowls). But a shallow shelf and heavy silting raise the cost of dredging ports (GS-I, GS-III).

• Disaster exposure differs by coast:

• The low, flat east coast faces cyclones and storm surges in October–December, and tsunamis (2004).
• The west coast faces heavy monsoon floods and landslides along the Ghats and on the Konkan rail route.

• Coastal hazard mapping and protection (mangroves, shelterbelts) are key policy responses (GS-III Disaster Management).

• Coastal wetlands under pressure: Chilika and Vembanad-Kol are Ramsar sites [4][5], but face silting, changes in salt levels, land reclamation, aquaculture and tourism pressure. Managing them sustainably supports fisheries, birds and livelihoods (GS-III Environment).

• Coastline revision and maritime planning: a longer coastline (11,098.81 km) [2] affects coastal security, Coastal Regulation Zone planning, the blue economy and port-led development under programmes such as Sagarmala (GS-III Infrastructure, Security).