The Northern Plains of India, the Thar Desert, and the North-Western landforms constitute a contiguous physiographic macro-region. Shaped primarily by the Indus, Ganga, and Brahmaputra river systems, this region represents the world’s largest alluvial tract. Understanding the spatial distribution, ecological significance, and depositional features like floodplains and riverine islands is critical for analyzing India’s physical geography.
Micro-Physiographic Divisions of the Northern Plains
The Northern Plains are classified into distinct geomorphological zones from the Shiwalik foothills to the deltaic regions based on relief, soil texture, and moisture retention.
| Region | Geomorphological Characteristics | Agricultural & Ecological Significance |
| Bhabar | Narrow belt (8–10 km wide) parallel to Shiwalik foothills; composed of un-sorted boulders and pebbles; high porosity leads to disappearing rivers. | Unsuitable for cultivation; dominated by deep-rooted forest trees. |
| Terai | Marshy, swampy zone south of Bhabar (10–20 km wide); re-emergence of underground streams; high humus and thick vegetation. | Highly fertile after reclamation; major belt for wheat, rice, and sugarcane; hosts Jim Corbett and Dudhwa National Parks. |
| Bhangar | Older alluvium forming alluvial terraces above flood limits; contains calcareous deposits known as Kankar; less fertile. | Requires intensive irrigation; prone to soil salinity (Reh or Kallar) in arid tracts. |
| Khadar | Newer, younger alluvium deposited by annual river floods; fine silt and clay composition; highly fertile. | Intensive agriculture; self-enriching soil system requiring minimal chemical fertilizers. |
Floodplains: Genesis, Mechanics, and Regional Variations
Floodplains are low-lying landforms adjacent to river channels, formed by continuous lateral accretion and vertical deposition of fine sediments during high-discharge periods.
Geomorphic Features of Floodplains
- Natural Levees: Elevated ridges formed along river banks due to the immediate deposition of coarser sediments during overflows. They act as natural embankments.
- Bluffs: Steep riverbanks marking the outer limit of a lateral migration zone or the edge of the older Bhangar terrace.
- Oxbow Lakes (Mortlake): Crescent-shaped water bodies formed when a meandering river cuts off a loop to create a straighter channel. Locally called Chors in Bihar and Beels in Bengal.
Regional Variations in Northern Indian Floodplains
- Punjab-Haryana Plains (Bet Lands): Floodplains in this region are locally termed Bet. The land between two rivers (Doabs) defines the topography, such as the Bist Doab (between Beas and Satluj) and Bari Doab (between Beas and Ravi).
- Ganga Plains (Khdir and Diara): The Middle Ganga plain features massive floodplains subject to frequent course shifting. The flood-prone islands within the river channel are called Diara land.
- Brahmaputra Valley: Characterized by a narrow floodplain (approx. 80 km wide) bounded by steep hill slopes, making it highly susceptible to catastrophic annual flooding and intense bank erosion.
Riverine Islands: Dynamics of Channel Bars
Riverine islands are landforms surrounded by river water, generated through sustained instream deposition, braiding of channels, and tectonic tilts. They occur predominantly in mature and old stages of river courses where gradient decreases and sediment load peaks.
Genesis of Riverine Islands
When a river carries heavy sediment loads down a steep gradient (e.g., Eastern Himalayas) and enters a flat plain, its velocity drops abruptly. The river cannot transport the entire load, leading to channel choking, bar formation, and subsequent braiding.
Major Riverine Islands of India
Majuli Island (Assam)
- Location: Brahmaputra River, Assam.
- Status: Declared the first river island district of India in 2016. It is bounded by the Brahmaputra River to the south and the Subansiri and Kherkutia Xuti (an anabranch) to the north.
- Culture & Ecology: Seat of Neo-Vaishnavite Sattras culture initiated by Srimanta Sankardeva. It faces severe existential threats due to extensive bank erosion.
Umananda Island (Assam)
- Location: Brahmaputra River, near Guwahati.
- Trivia: Known as the smallest inhabited riverine island in the world. Also called Peacock Island by British administrators due to its shape. It hosts the 17th-century Umananda Temple.
Srirangam and Srirangapatna Islands
- Location: Cauvery River (Southern Peninsula, but relevant as comparative riverine systems). Created by the bifurcation of the Cauvery river channel into northern (Kollidam) and southern branches.
North-Western Landforms and the Indian Desert (Thar)
The North-Western landform unit shifts from the fertile Indus plain into the arid and semi-arid ecosystem of the Thar Desert (Marusthali) and its transitional zone (Bagari).
Geomorphological Features of the Thar Desert
- Marusthali: The true desert region characterized by shifting sand dunes (Dhrian).
- Rajasthan Bagar: The semi-arid transitional plain between Marusthali and the Aravalli Range, drained by short seasonal streams.
- Playas and Dhand: Shallow, ephemeral salt lakes located in internal drainage basins. Examples include Didwana, Kuchaman, and Sambhar Lake (India’s largest inland salt lake).
Paleofloodplains and Lost River Systems
- The Ghaggar-Hakra System: Considered the remnants of the ancient Saraswati River. The dry bed of this river acts as a paleofloodplain, featuring rich alluvial deposits beneath the desert sand, supporting localized agriculture (e.g., Ganganagar district).
- Luni River Basin: The only major integrated river system in the desert. It originates in the Pushkar valley of the Aravalli Range and terminates in the marshy lands of the Rann of Kutch. Its upper courses are fresh, while the lower courses become highly saline past Balotra due to high atmospheric evaporation and salt-rich subsoil.
Prelims-Centric Fact File
- Barind Plains: Deltaic dynamic formations in the lower Ganga-Brahmaputra plain composed of old alluvium, often characterized by lateritic clay formations.
- Chos: Seasonal torrents originating from the Shiwalik hills that cause severe soil erosion in the Punjab plains, particularly in the Hoshiarpur district.
- Kankar: Nodular calcium carbonate segregations found in the Bhangar soil layer, indicating poor leaching and high evaporation rates.
- Bh重复/Bhur: Isolated wind-blown sand accumulations forming ridges along the banks of rivers in the upper Ganga-Yamuna Doab.