India - Drainage Systems

In physical geography and fluvial geomorphology, a Drainage System refers to the integrated flow network of surface water through definite channels, streams, and rivers governed by gravity, slope gradient, and rock resistance.

• Drainage Basin (River Catchment): The specific territorial area drained by a master river along with all its tributaries and distributaries. India's largest river basin is the Ganga basin, encompassing over 860,000 km² in India alone.
• Water Divide (Watershed / Drainage Divide): An elevated geographical feature, such as a mountain ridge or plateau highland, that separates adjacent drainage basins. Surface runoff on opposite slopes travels to distinct river systems.
  • Delhi Ridge & Aravalli Range: Separates the westward-flowing Indus river system from the eastward-flowing Ganga system.
  • Satpura & Vindhyan Ranges: Separates the North Indian Gangetic drainage from the Peninsular Deccan drainage.
  • Western Ghats (Sahyadris): The primary continental water divide of peninsular India, separating short, torrential west-flowing rivers (Arabian Sea) from extensive east-flowing rivers (Bay of Bengal).
• Antecedent vs. Superimposed Drainage:
  • Antecedent Drainage (পূর্ববর্তী নদী): Rivers that existed before the uplift of a mountain barrier and maintained their established courses by incising deep, steep-walled gorges at a rate matching or exceeding the rate of tectonic uplift. Examples: Indus, Satluj, Brahmaputra, Subansiri, Arun (tributary of Kosi).
  • Superimposed Drainage (অধ্যারোপিত নদী): A river system that developed on an initial covering stratum of rock and subsequently cut down into discordantly structured underlying older geological formations. Examples: Subarnarekha, Chambal, Banas, Damodar.

The geometric arrangement and spatial configuration formed by streams in a drainage basin reflect underlying geological structures, rock hardness, and regional slope:

The Himalayan river network originates in the perennial snowfields and high glaciers of the Trans-Himalayan and Greater Himalayan zones. Key diagnostic features include:

• Perennial Regime: Fed by both seasonal monsoonal rains (July-September) and summer glacial meltwater (April-June), ensuring perennial water discharge throughout the year.
• Youthful Dynamic Stage: Deep narrow V-shaped valleys, dramatic river gorges (such as the 5,180 m Indus gorge near Gilgit and the Dihang gorge at Namcha Barwa), steep gradients, rapids, and cascading waterfalls in their upper reaches.
• Heavy Siltation & Meandering: Massive silt loads deposited upon entering the flat plains, leading to braided channels, oxbow lakes, riverine islands, and catastrophic avulsion (channel-shifting).

The Indus (Sanskrit: Sindhu) is one of the world's greatest river systems, with a total length of approximately 2,880 km (1,114 km within Indian territory) and a total drainage basin of 1,165,000 km² (321,289 km² in India).

• Origin: Glacial melt at Bokhar Chu near Mount Kailash in the Tibetan plateau (~4,164 m elevation). Known in Tibet as the Singi Khamban ("Lion's Mouth").
• Course in India: Flows northwest between the Ladakh and Zaskar ranges, cuts through Ladakh at Leh, traverses the stunning Rondu gorge, and enters Pakistan near Chilas in the Dardistan region.
• Right-Bank Tributaries: Shyok (River of Death), Gilgit, Hunza, Shigar, Gasting, Dras, Kabul, Kurram, Tochi, and Gomal.
• Left-Bank Tributaries (The Panjnad - পাঁচ নদী):
  • Jhelum (ঝিলাম / वितस्ता): Originates at Verinag spring at the foot of Pir Panjal in Kashmir; flows through Srinagar and Wular Lake; forms Indo-Pak border before joining Chenab at Jhang.
  • Chenab (চন্দ্রভাগা / अस्किनी): Largest Indus tributary by discharge; formed by the confluence of two mountain torrents, Chandra and Bhaga, at Tandi near Keylong in Himachal Pradesh; cuts across Pir Panjal.
  • Ravi (ইরাবতী / परुष्णी): Originates in the Kullu hills near Rohtang Pass in Himachal Pradesh; flows between Pir Panjal and Dhauladhar ranges.
  • Beas (বিপাশা / विपाशा): Originates at Beas Kund near Rohtang Pass; cuts an impressive gorge at Larji; lies entirely within Indian territory, merging with the Satluj at Harike barrage (Punjab).
  • Satluj (শতদ্রু / शतद्रु): An antecedent river originating at Rakas Lake (Rakshastal) near Mansarovar in Tibet (~4,555 m); known as Langchen Khambab; cuts through the Zaskar range and enters India through Shipki La pass; feeds the Bhakra Nangal multi-purpose reservoir (Govind Sagar).
• Indus Waters Treaty (1960): Brokered by the World Bank between India and Pakistan. Allocates exclusive rights over the three eastern rivers (Ravi, Beas, Satluj) to India, while Pakistan receives the waters of the three western rivers (Indus, Jhelum, Chenab), subject to limited non-consumptive and run-of-the-river hydroelectric usage by India.

Originating from the Chemayungdung glacier of the Kailash range southeast of Lake Mansarovar at an altitude of 5,150 m:

• Tibetan Course: Known as the Tsangpo ("The Purifier"). Flows eastward for nearly 1,200 km through southern Tibet parallel to the main Himalayan axis as a sluggish, high-altitude stream.
• The Great U-Turn & Namcha Barwa: Near Namcha Barwa peak (7,757 m), the river executes a dramatic hairpin turn, carving out the world's deepest canyon (Yarlung Tsangpo Grand Canyon), and enters India through Arunachal Pradesh under the name Siang and then Dihang.
• Assam Valley & Brahmaputra formation: Near the town of Sadiya, the Dihang is joined by two torrential mountain rivers from the east: the Dibang and the Lohit. From this confluence onward, the river is known as the Brahmaputra ("Son of Brahma").
• Hydrological Features:
  • Braided Channel & Majuli Island: Carries an immense sediment load due to high seismicity, steep slopes, and excessive rainfall in Assam and Arunachal Pradesh. The braided channel hosts Majuli, recognized as the world's largest inhabited freshwater riverine island and India's first river island district.
  • Major Tributaries: Right-bank: Subansiri (antecedent), Kameng, Manas, Sankosh, and Teesta. Left-bank: Burhi Dihing, Dhansiri, and Kopili.
  • Course in Bangladesh: Enters Bangladesh near Dhubri, where it is called the Jamuna. It merges with the Padma (Ganga) at Goalundo and later with the Meghna before debouching into the Bay of Bengal.

The Ganga is the national river of India, extending across 2,525 km. Its headstream, the Bhagirathi, rises from the Gaumukh ice-cave of the Gangotri Glacier in Uttarkashi district of Uttarakhand at an elevation of 3,892 m. The Alaknanda rises from the Satopanth and Bhagirath Kharak glaciers above Badrinath.

The holy confluence network of the Garhwal Himalayas forms the famous Panch Prayag (পঞ্চপ্রয়াগ), an essential sequence for board examinations:

The Ganga debouches from the Siwalik hills onto the northern alluvial plains at Haridwar. Traversing Uttarakhand, Uttar Pradesh, Bihar, and West Bengal, it receives major left-bank and right-bank tributaries:

• Right-Bank Tributaries:
  • Yamuna (যমুনা): Longest and westernmost tributary of the Ganga (1,376 km). Rises from the Yamunotri glacier on the Bandarpoonch peak. Flows parallel to the Ganga, joining it on the right bank at Prayagraj (Triveni Sangam). Its major tributaries include the Chambal (famous for ravines and badland topography), Sind, Betwa, and Ken.
  • Son (শোন): Originates at the Amarkantak plateau; cuts through the Kaimur hills and joins the Ganga just upstream of Patna.
  • Damodar: Historically joins the Hooghly in lower Bengal.
• Left-Bank Tributaries:
  • Ramganga: Rises in Garhwal hills, joins Ganga near Kannauj.
  • Gomti: Ground-fed river originating from Gomat Taal (Fulhar Jheel) in Pilibhit; Lucknow is situated on its banks.
  • Ghaghara (ঘর্ঘরা / Karnali): Rises in the Mapchachungo glacier of Tibet; carries the largest volume of water among all Ganga tributaries; joins near Chhapra.
  • Gandak (গণ্ডক): Rises near the Nepal-Tibet border between Dhaulagiri and Mount Everest; joins Ganga at Sonpur near Patna.
  • Kosi (কোশী): Formed by seven streams (Saptakoshi); main stream Arun is an antecedent river originating in Tibet; notorious as the 'Sorrow of Bihar' due to frequent devastating floods and westward channel migration (over 120 km in the last 250 years).
  • Mahananda: Rises in the Darjeeling hills; acts as the last left-bank tributary of the Ganga in India before bifurcation.

At Farakka in Murshidabad district (West Bengal), the Ganga bifurcates into two distinct distributary channels:

1. Bhagirathi-Hooghly (ভাগীরথী-হুগলী): Flows southwards through the Rarh and deltaic plains of West Bengal past Kolkata and Haldia, entering the Bay of Bengal near Sagar Island.
2. Padma (পদ্মা): The main hydraulic volume enters Bangladesh as the Padma, receives the Jamuna (Brahmaputra), and later joins the Meghna to form the world's largest fluvio-marine delta: the Ganga-Brahmaputra Delta (Sundarbans).

The Peninsular drainage system is geologically far older than the Himalayan system. The rivers flow through wide, shallow, and senile valleys, having attained graded profiles (base level of erosion). Key evolutionary factors include:

• Subsidence of Western Flank: Submergence of the western flank of the Peninsular block during the Tertiary period created the Western Ghats escarpment and interrupted the original symmetrical drainage.
• Slight Tilt of Peninsular Block: Tectonic tilting of the Deccan plateau from northwest to southeast directed the major river systems toward the Bay of Bengal.
• Trough Faulting (Rift Valleys): Formation of linear grabens and down-faulted rift valleys between the Vindhya and Satpura ranges allowed the Narmada and Tapi to flow westward in opposition to the general peninsular tilt.

Unlike east-flowing rivers, west-flowing rivers do not build deltas; instead, they empty into the sea via deep estuaries, rocky drowned inlets, and tidal lagoons:

• Narmada (নর্মদা): Longest west-flowing river (1,312 km). Rises from the Amarkantak plateau (~1,057 m) in Madhya Pradesh. Flows westward through a magnificent rift valley bounded by the Vindhyan range to the north and the Satpura range to the south. Cascades over the picturesque Dhuandhar Falls in white marble rocks near Jabalpur. Major dam: Sardar Sarovar Dam (Gujarat). Empties into the Gulf of Khambhat through a 27-km-long funnel-shaped estuary.
• Tapi / Tapti (তাপ্তি): Second major west-flowing river (724 km). Rises in Multai in the Betul district of Madhya Pradesh on the Satpura plateau. Flows parallel to Narmada in a rift valley south of the Satpuras through Maharashtra, MP, and Gujarat. Major multi-purpose projects: Ukai Dam and Kakrapar Project. Enters Gulf of Khambhat near Surat.
• Other Significant West-Flowing Streams:
  • Sabarmati: Originates in Aravalli range (Udaipur, Rajasthan); flows through Ahmedabad into Gulf of Khambhat.
  • Mahi: Originates in Vindhyan hills (MP); cuts across the Tropic of Cancer twice; empties into Gulf of Khambhat.
  • Luni (লুনি): Primary river of inland drainage in the Thar Desert. Originates near Pushkar (Ajmer) in the Aravallis, flows southwest, and dissipates into the marshy flats of the Rann of Kutch. Its water is fresh up to Balotra and turns saline downstream.
  • Goan Rivers: Mandovi and Zuari (vital waterways supporting iron ore transport; Marmagao port situated on Zuari estuary).
  • Karnataka Rivers: Sharavathi (famous for Jog/Gersoppa Falls, 253 m high), Kali, Netravati.
  • Kerala Rivers: Periyar (longest river of Kerala, 244 km; Idukki arch dam), Bharathapuzha (largest basin area), Pamba (drains into Vembanad Lake).

For WBCHSE higher secondary examinations, mastering the drainage network of West Bengal is mandatory. The state's rivers are classified into three distinct physiographic groups:

Characterized by snowmelt and torrential monsoonal precipitation, high velocity, steep gradient, heavy boulder/gravel transportation, and frequent shifting of river beds in the Terai and Dooars:

• Teesta (তিস্তা - Lifeline of North Bengal): Originates from the Pauhunri glacier (Tso Lhamo Lake) in North Sikkim (~7,068 m). Carves a deep gorge through the Darjeeling Himalayas, joined by the Rangeet (Great Rangit) at Teesta Bazaar. Enters the plains at Sevoke near Siliguri, flows through Jalpaiguri, enters Bangladesh, and merges with the Jamuna (Brahmaputra). Historical shift: Prior to the catastrophic 1787 floods, Teesta was a tributary of the Ganga; flood avulsion diverted it eastward into the Brahmaputra system.
• Torsa (তোর্সা): Originates in the Chumbi Valley of Tibet (known as Amo Chu); flows through Bhutan and Alipurduar district (past Jaldapara National Park); enters Bangladesh to join the Jamuna.
• Jaldhaka (জলঢাকা): Originates from Bitang Lake in southeast Sikkim; flows through Bhutan, Kalimpong, Jalpaiguri, and Cooch Behar; historic hydro-project at Jhalong.
• Mahananda (মহানন্দা): Originates in the Mahaldiram hills near Kurseong (Darjeeling district); flows past Siliguri and Malda; serves as an important tributary meeting the Ganga at Godagari (Bangladesh border). Major tributaries include Balason and Mechi.
• Other North Bengal Streams: Kaljani, Raidak, Sankosh (forms West Bengal-Assam boundary).

Originating from the ancient Chota Nagpur Plateau, these rivers are rain-fed and non-perennial, exhibiting torrential flash floods during peak monsoon months and drying up into sandy trickles during summer:

• Damodar (দামোদর - 'Sorrow of Bengal' / বাংলার দুঃখ): Originates at Khamarpat hill on the Chota Nagpur plateau (Palamu, Jharkhand). Flows eastward across Purulia, Bankura, Burdwan, and Hooghly districts. Known historically for devastating floods in lower Bengal. Tamed by India's premier multi-purpose river valley project: the Damodar Valley Corporation (DVC), established in 1948 on the model of the Tennessee Valley Authority (TVA) in the USA. Multi-purpose dams: Tilaiya, Maithon, Konar, and Panchet, along with the Durgapur Barrage. Empties into the Hooghly river near Shyampur.
• Rupnarayan (রূপনারায়ণ): Formed by the confluence of the Dwarkeswar and Silabati (Silai) near Ghatal in Paschim Medinipur; joins the Hooghly at Geonkhali.
• Kangsabati / Kansai (কংসাবতী): Originates in the Chota Nagpur hills in Purulia; united with Kumari river where the vast Mukutmanipur Dam (second largest earthen dam in India) is constructed.
• Mayurakshi (ময়ূরাক্ষী): Originates in the Trikut hills of Deoghar (Jharkhand); site of the Massanjore Dam (also called Canada Dam); flows through Birbhum and Murshidabad into the Bhagirathi.
• Subarnarekha (সুবর্ণরেখা): Originates near Ranchi; traverses Purulia, Jharkhand, and Odisha; famous for Hundru Falls; carries traces of alluvial placer gold in its riverbed sands.

In the low-lying active delta of the Sundarbans (South and North 24 Parganas), channels are interconnected tidal inlets rather than conventional fresh streams. Rivers such as the Matla, Gosaba, Bidyadhari, Raimangal, Saptamukhi, Thakuran, and Jamira are fed by marine tidal influx twice daily. Siltation has disconnected many from their upstream freshwater sources, increasing salinity and exacerbating erosion during cyclonic storm surges.

Tidal Bore (বাণ ডাকা / Tidal Surge): In the funnel-shaped estuary of the Hooghly River, incoming spring tides clash against the opposing river current, generating a steep, roaring wall of tidal water several meters high that travels upstream past Diamond Harbour and Kolkata.

A River Regime represents the seasonal pattern of discharge and water flow volume across a calendar year, typically illustrated by an annual discharge hydrograph:

• North Indian Himalayan Regime: Demonstrates a bimodal (double-peaked) hydrograph:
  1. First Peak (May - June): Accelerated melting of Himalayan snow and glaciers during late spring and early summer.
  2. Second and Dominant Peak (July - September): Torrential precipitation brought by the Southwest Monsoon. Discharge drops to low levels during the dry winter (December - February).
• South Indian Peninsular Regime: Demonstrates a unimodal (single-peaked) hydrograph with extreme seasonal fluctuations:
  • Discharge peaks sharply in July-August following torrential monsoon downpours.
  • During the dry winter and summer months (March - May), runoff plummets dramatically; smaller tributaries dry up completely due to lack of glacial sources.
  • Exception: The Kaveri River maintains a balanced, double-season regime because its upper catchment receives the Southwest Monsoon and its lower catchment receives the retreating Northeast Monsoon.

To mitigate the paradox of concurrent floods in eastern India and severe droughts in western and peninsular regions, the Ministry of Jal Shakti and National Water Development Agency (NWDA) formulated the National River Linking Project, divided into two major components:

1. Himalayan Component (14 Links): Transfers surplus floodwaters from the Ganga and Brahmaputra basins to the west (Indus basin) and south (Mahanadi basin).
2. Peninsular Component (16 Links): Interlinks peninsular rivers, including the Ken-Betwa Link Project (KBLP), India's first operational river interlinking project designed to irrigate the drought-prone Bundelkhand region across MP and UP.

Rapid industrialization, discharge of untreated municipal sewage, chemical fertilizer runoff, and intensive dam impoundments have severely degraded the ecological health of Indian rivers:

• Namami Gange Programme: An integrated flagship mission launched in 2014 by the Government of India with a comprehensive budget to accomplish the dual objectives of effective abatement of pollution and conservation/rejuvenation of the National River Ganga. Pillars include:
  • Sewage Treatment Infrastructure (creating modern STPs to stop direct discharge of municipal blackwater).
  • River-Front Development & Ghat Cleaning (e.g., at Varanasi, Haridwar, Kanpur).
  • River Surface Cleaning & Biodiversity Conservation (Gangetic Dolphin, Gharial, Golden Mahseer).
  • Afforestation along riverbanks and organic farming in riparian buffer corridors.
• Concept of Environmental Flow (E-Flow): The minimum guaranteed quantity, timing, and quality of freshwater flow required downstream of dams and barrages to sustain freshwater ecosystems, maintain navigation, dilute effluents, and preserve river geomorphology.