Eastern Coastal Plains

Introduction

The Eastern Coastal Plains form a broad, continuous lowland belt along India’s eastern seaboard, stretching approximately 1,600 km from the Subarnarekha River near the West Bengal-Odisha border to Kanyakumari at the southern tip. In contrast to the narrow and deeply indented western coast, the eastern plains are significantly wider — ranging from 100 to 130 km in width — and are characterized by the development of massive deltas at the mouths of the peninsular rivers. These plains represent one of India’s most fertile and densely populated agricultural regions, supporting intensive rice cultivation and extensive aquaculture.

Geomorphological Origin and Characteristics

The eastern coastal plains are predominantly a coastline of emergence — the land has risen relative to sea level or the sea has withdrawn, exposing former seabed areas. This emergence is related to the ongoing post-Pleistocene epeirogenic uplift of the eastern continental margin, accompanied by the enormous sediment deposition from the east-flowing peninsular rivers that have built deltas progressively seaward. Key geomorphological features include:

Deltaic Formation: The major rivers of the Deccan — Mahanadi, Godavari, Krishna, and Kaveri — descend from the Western Ghats, traverse the entire width of the peninsula, and deposit their sediment loads upon reaching the gentler gradients of the coastal plain, forming extensive deltas. The delta formation on the east coast compared to the absence of significant deltas on the west coast (except the Narmada-Tapti) is explained by the longer river courses, larger catchment areas, higher sediment loads, and the emergent nature of the eastern coastline that favors deltaic progradation rather than estuary formation.

Continental Shelf: The continental shelf on the eastern seaboard is relatively wide — averaging 50-120 km — compared to the narrow shelf (10-40 km) on the west coast. This wider shelf, rich in sediment and nutrients, supports productive fishing grounds particularly in the Bay of Bengal.

Sand Dunes and Beach Ridges: Extensive parallel beach ridges (locally called “teris” in Tamil Nadu) aligned parallel to the coastline preserve records of Holocene sea-level fluctuations. The Teri sands of the Tirunelveli and Thoothukudi districts contain archaeological evidence of microlithic human settlements that exploited coastal resources approximately 7,000-3,000 years before present.

The Utkal Coast (Odisha Coast)

The northern segment of the eastern coastal plains, extending from the Subarnarekha River delta to the Chilika Lake, is known as the Utkal Coast. This coastal stretch of approximately 450 km in Odisha is characterized by two major features:

The Mahanadi Delta: The combined delta of the Mahanadi, Brahmani, and Baitarani rivers forms one of India’s largest coastal sedimentary landforms, covering approximately 10,500 square kilometers. The delta is highly active, with distributary channel migration and coastal erosion-accretion cycles. The Bhitarkanika mangrove ecosystem within the delta — designated a Ramsar Wetland of International Importance — supports the largest nesting colony of olive ridley turtles (Lepidochelys olivacea) in the Indian Ocean and contains significant saltwater crocodile (Crocodylus porosus) populations.

Chilika Lake: Asia’s largest brackish water lagoon and India’s largest coastal lagoon, Chilika covers a variable area of 900-1,165 square kilometers depending on the season. Separated from the Bay of Bengal by a 60 km sand spit — effectively a barrier beach — Chilika is connected to the sea through a narrow mouth that was manually dredged in 2000 to restore the lagoon’s salinity regime and ecosystem. The lagoon is designated as India’s first Ramsar Wetland of International Importance (1981) and hosts over one million migratory waterfowl annually from as far as Siberia, the Caspian, and Ladakh during winter. The lake’s rich fisheries support over 200,000 local fisherfolk.

The Northern Circars Coast (Andhra Coast)

Extending approximately 550 km from Chilika Lake to the Pulicat Lake, the Northern Circars coast of Andhra Pradesh is dominated by the Godavari and Krishna deltas:

The Godavari Delta: With an area exceeding 12,000 square kilometers, the Godavari possesses India’s second-largest delta (after the Ganga-Brahmaputra). The river bifurcates at Dowleswaram into two major distributary systems — the Gautami flowing east and the Vasishta flowing south — each further subdividing into numerous branches before reaching the Bay of Bengal. The Kolleru Lake, a freshwater wetland of 245-900 square kilometers (seasonally variable) situated between the Godavari and Krishna deltas, serves as a critical flood-buffering system and bird habitat, designated a Ramsar site in 2002.

The Krishna Delta: The Krishna River begins its deltaic distributaries near Vijayawada, with the Prakasam Barrage regulating irrigation waters. The delta covers approximately 6,500 square kilometers and supports intensive rice cultivation, with the Nagarjuna Sagar project providing controlled irrigation.

The Coromandel Coast

The southern segment of the eastern plains, from Pulicat Lake to Kanyakumari, is historically known as the Coromandel Coast (deriving from “Cholamandalam” — the land of the Cholas). This coastal plain of Tamil Nadu is distinguished by:

Pulicat Lake: The second-largest brackish water lagoon in India (approximately 450 square kilometers), straddling the Andhra Pradesh-Tamil Nadu border. The barrier island of Sriharikota, separating Pulicat from the Bay of Bengal, hosts the Satish Dhawan Space Centre — India’s primary satellite launch facility. Pulicat is an important habitat for flamingos and supports traditional fishing communities.

The Kaveri Delta: The Kaveri River forms a classic fan-shaped delta in central Tamil Nadu covering approximately 10,000 square kilometers. This delta, built by the river’s numerous distributaries including the Kollidam (Coleroon), Vennar, and Arasalar, represents one of the oldest continuously cultivated landscapes in the world, with the Grand Anicut (Kallanai), built by the Chola king Karikalan in the 2nd century CE, being among the world’s oldest functioning water-diversion structures. The delta is the rice bowl of Tamil Nadu and is historically associated with high population density and sophisticated tank (eri)-based irrigation systems.

Coraline Islands: The Gulf of Mannar, between the Tamil Nadu coast and Sri Lanka’s northwest coast, features 21 low-lying coral islands — designated the Gulf of Mannar Marine National Park in 1986 and recognized as a UNESCO Biosphere Reserve in 2001. These islands and associated coral reefs support approximately 3,600 species of flora and fauna, including the endangered dugong (Dugong dugon). The Adam’s Bridge (Rama Setu) — a chain of limestone shoals between Pamban Island and Mannar Island in Sri Lanka — represents a geological formation of sandbanks and coral reefs that some theories suggest was a land connection during periods of lowered Pleistocene sea level.

The eastern coastal plain’s port infrastructure includes Paradip (Odisha), Visakhapatnam (Andhra Pradesh — one of India’s deepest landlocked natural harbors), Chennai (Tamil Nadu’s major port with an artificial harbor), and Thoothukudi (Tuticorin). The Ennore Port near Chennai and the recently developed Krishnapatnam and Gangavaram ports (both in Andhra Pradesh) represent newer deep-water facilities on this coast.