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Northern Plains - Regional Divisions

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Introduction

The Northern Plains of India, while forming a continuous alluvial belt, exhibit significant regional variations in topography, drainage, soils, climate, and agricultural patterns. The traditional tripartite division — Punjab-Haryana Plains in the west, Ganga Plains in the center, and the Brahmaputra Plains in the east — provides a framework for understanding the physiographic and cultural diversity of this densely populated region. The regional divisions are separated by the Delhi Ridge (Aravalli outcrop) in the west and the Rajmahal-Garo gap in the east.

The Punjab-Haryana Plains (Indus Tributary Plains)

Extending from the Indus River boundary in the west to the Delhi Ridge-Aravalli axis in the east, these plains cover approximately 1.75 lakh square kilometers across Punjab, Haryana, and adjacent areas. The region is characterized by a unique interfluve landscape known as the Doabs (from Persian “do-ab” meaning two waters). Five major doabs are recognized between the Indus tributaries in their downstream reaches:

  • Bist Doab: Between the Beas and Satluj rivers
  • Bari Doab: Between the Beas and Ravi rivers (home to the city of Lahore)
  • Rechna Doab: Between the Ravi and Chenab rivers
  • Chaj Doab: Between the Chenab and Jhelum rivers
  • Sindh Sagar Doab: Between the Indus and Jhelum-Chenab combined channels

The Punjab Plains exhibit a gentle slope from northeast (approximately 400 meters near the foothills) to southwest (approximately 180 meters near the Rajasthan border). This slope, averaging about 30 cm per kilometer, determines the southwesterly drainage direction. The Ghaggar River, now a seasonal and often dry channel, represents a former course of the Satluj or possibly the ancient Saraswati River described in Vedic texts. The region receives 400-900 mm of annual rainfall, decreasing southwestward, with irrigation through an extensive canal network (dating from the British era and expanded after Independence) being essential for agriculture. The Indus Waters Treaty (1960) between India and Pakistan governs the sharing of these transboundary rivers.

The Ganga Plains

The Ganga Plains constitute the central and most extensive portion of the Northern Plains, stretching from the Yamuna River in the west to the western boundary of West Bengal state in the east, and from the Himalayan foothills in the north to the Peninsular craton in the south. Covering approximately 3.5 lakh square kilometers, these plains span the states of Uttar Pradesh, Bihar, and parts of Haryana, Delhi, and West Bengal.

Upper Ganga Plains: Comprising western and central Uttar Pradesh, this sub-region is drained by the Yamuna, Ganga, Ramganga, and Gomti rivers. The land slopes gradually east-southeastward, with elevations ranging from 300 meters in the north to 70 meters near Allahabad (Prayagraj). The interfluves here are relatively stable, wider, and well-defined. Allahabad marks the sacred confluence (Triveni Sangam) of the Ganga, Yamuna, and the mythical Saraswati. The Bhangar-Bhur formations represent older upland surfaces, while the extensive khadar lowlands adjacent to the rivers support intensive cultivation.

Middle Ganga Plains: Covering eastern Uttar Pradesh and Bihar, this sub-region receives higher rainfall (1,000-1,500 mm) and is characterized by greater fluvial dynamism. The Ganga here is joined by major Himalayan tributaries — the Ghaghara, Gandak, and Kosi — each contributing enormous sediment loads and exhibiting significant channel migration. The Kosi River particularly exemplifies this instability, having shifted westward by over 110 km since 1736, earning it the sobriquet “Sorrow of Bihar.” The convergence of multiple large rivers creates extensive flood-prone areas, with annual flooding affecting millions of hectares despite extensive embankment systems.

Lower Ganga Plains: In West Bengal, the Ganga (known as the Hooghly or Bhagirathi in its distributary form) branches into the deltaic distributaries that ultimately form the Sundarbans delta. This sub-region represents a transition from alluvial plains to deltaic environments, with declining river gradients, extensive wetlands, tidal influences, and the spread of rice-based agriculture. The Rarh region in western West Bengal represents an older, slightly elevated lateritic surface marking the boundary with the Chota Nagpur Plateau.

The Brahmaputra Plains

The Brahmaputra Plains in Assam represent a distinct physiographic province, separated from the main Ganga Plains by the Rajmahal-Garo gap where the river forces its way southward to enter Bangladesh. Covering approximately 56,000 square kilometers, these plains are narrower (80-100 km) than the Ganga Plains and are bounded by the Eastern Himalaya in the north, the Patkai-Naga Hills in the east, and the Meghalaya Plateau (Shillong Plateau) and Mikir Hills in the south.

The Brahmaputra is a highly braided river with exceptional discharge (average 19,830 cubic meters per second at Pandu, Guwahati) and sediment load that shapes a dynamic floodplain. The river gradient is steep (approximately 13 cm per km in the upper reaches, declining to 8 cm per km in the lower valley), contributing to its erosive power and transport capacity. Numerous riverine islands (chars) appear and disappear with shifting channels — Majuli Island in the Brahmaputra, once the world’s largest river island, has been reduced from approximately 1,250 square kilometers to about 550 square kilometers due to severe bank erosion. Annual flooding submerges 30-40% of the state’s area, making flood management the central challenge of Assam’s geography.

The valley is flanked by alluvial fans (notably the Manas, Subansiri, and Dibang fans) where Himalayan tributaries enter the plains. The Brahmaputra Plains receive 2,000-3,000 mm of annual rainfall, supporting lush natural vegetation transitioning to tea gardens and paddy cultivation on the higher terraces.