Major River Systems of India
Himalayan Rivers (Perennial)
Indus System:
- Indus (Sindhu): originates near Mansarovar Lake, Tibet. Flows through Ladakh, Pakistan. Total length 3,180 km.
- Tributaries in India: Jhelum, Chenab, Ravi, Beas, Sutlej (the five rivers of Punjab)
- Indus Waters Treaty (1960): India and Pakistan share Indus waters — India gets eastern rivers (Ravi, Beas, Sutlej); Pakistan gets western rivers (Indus, Jhelum, Chenab)
Ganga System:
- Ganga originates at Gangotri glacier (Uttarakhand); joins Bay of Bengal at Sagar Island (West Bengal)
- Length: 2,525 km; basin: 8.6 lakh sq km
- Key tributaries: Yamuna, Son, Ghaghra, Gandak, Kosi (from north); Chambal, Betwa (from south)
- Brahmaputra (Tsangpo in Tibet): originates near Mansarovar; enters India at Arunachal Pradesh; joins Ganga in Bangladesh (as Jamuna); forms world's largest river delta — Sundarbans
Peninsular Rivers (Seasonal, mostly eastward-flowing)
| River | Origin | Drains into | States Covered |
|---|---|---|---|
| Mahanadi | Chhattisgarh | Bay of Bengal | Chhattisgarh, Odisha |
| Godavari | Nashik (Maharashtra) | Bay of Bengal | Maharashtra, Telangana, AP |
| Krishna | Mahabaleshwar (Maharashtra) | Bay of Bengal | Maharashtra, Karnataka, AP, Telangana |
| Cauvery | Talakaveri (Kodagu, Karnataka) | Bay of Bengal | Karnataka, Tamil Nadu |
| Vaigai | Varushnad hills (Dindigul) | Bay of Bengal | Tamil Nadu |
| Tamiraparani | Agasthyamalai (Tirunelveli) | Bay of Bengal | Tamil Nadu |
West-flowing exceptions (unusual for Peninsular rivers):
- Narmada: Amarkantak Plateau (MP) → Arabian Sea. Flows through a rift valley. Total length 1,312 km.
- Tapti (Tapi): Betul district (MP) → Arabian Sea. Also flows through a rift valley.
Tamil Nadu Rivers
Cauvery (Kaveri)
- Origin: Talakaveri spring, Brahmagiri Hills, Kodagu (Coorg), Karnataka (alt. 1,341 m)
- Length: 805 km; basin: 81,155 sq km
- Enters Tamil Nadu at Hogenakal (waterfall)
- Mettur Dam (Stanley Reservoir): built 1934, on Cauvery at Salem district. Storage: 93.47 TMC. Largest dam in Tamil Nadu.
- Major tributaries: Hemavati, Kabini, Bhavani, Noyyal, Amaravathi
- Delta: Thanjavur, Tiruvarur, Nagapattinam districts — "rice bowl of Tamil Nadu"
- Cauvery river dispute: Between Karnataka and Tamil Nadu (see FAQ above)
Other Major Tamil Nadu Rivers
| River | Origin | Districts | Notes |
|---|---|---|---|
| Palar | Kolar (Karnataka) | Vellore, Ranipet, Chengalpattu | North Tamil Nadu; seasonal |
| Pennaiyar (Ponnaiyar) | Nandi Hills (Karnataka) | Krishnagiri, Villupuram | Krishnagiri Reservoir |
| Vaigai | Varushnad Hills (Dindigul) | Madurai, Ramanathapuram | Vaigai Dam near Madurai |
| Tamiraparani | Agasthyamalai (Tirunelveli) | Tirunelveli, Thoothukudi | Perennial; flows to Gulf of Mannar |
| Bhavani | Nilgiris | Erode | Joins Cauvery; Bhavani Sagar Dam |
| Noyyal | Vellingiri Hills (Coimbatore) | Coimbatore, Tiruppur, Erode | Joins Cauvery |
| Amaravathi | Anamalai Hills | Tiruppur, Karur | Joins Cauvery |
Lakes in Tamil Nadu
- Pulicat Lake: 2nd largest brackish water lagoon in India (after Chilika, Odisha). Straddles TN-AP border. Important for flamingoes.
- Kolleru Lake: AP (note: not TN — common confusion in exams)
- Veeranam Lake: Cuddalore district; supplies water to Chennai along with Poondi.
- Chembarambakkam and Red Hills: Chennai's main water supply reservoirs.
- Ooty Lake (Udhagamandalam Lake): Artificial lake, built by John Sullivan in 1824.
Major Dams of India
| Dam | River | State | Purpose |
|---|---|---|---|
| Tehri Dam | Bhagirathi (Ganga) | Uttarakhand | Hydropower, irrigation — India's tallest dam (260 m) |
| Bhakra-Nangal | Sutlej | Himachal Pradesh/Punjab | Irrigation, hydropower — Nehru called it "temple of modern India" |
| Hirakud Dam | Mahanadi | Odisha | Flood control, irrigation — longest dam in India (25.8 km) |
| Nagarjuna Sagar | Krishna | Telangana/AP | Irrigation — one of the world's largest masonry dams |
| Tungabhadra Dam | Tungabhadra | Karnataka | Irrigation, hydropower — supplies water to Hampi |
| Sardar Sarovar | Narmada | Gujarat | Irrigation, power — controversial due to displacement |
| Mettur Dam (Stanley) | Cauvery | Tamil Nadu | Irrigation — opens June 12 for Kuruvai crop season |
| Idukki Dam | Periyar | Kerala | Hydropower — India's first and largest arch dam |
Indian Climate and Monsoon
Climate Types in India (Köppen Classification)
India has a wide range of climates:
- Tropical monsoon (Am): Most of peninsular India including Tamil Nadu
- Tropical wet and dry (Aw): Interior Deccan
- Humid subtropical (Cfa): Northern plains, West Bengal
- Arid/Semi-arid (BWh/BSh): Rajasthan, parts of Gujarat, Deccan rain shadow
- Alpine/Tundra: High Himalayas, Ladakh
- Temperate (Cfb): Parts of Northeast, some Himalayan slopes
Monsoon Mechanism
India's climate is dominated by the monsoon — the seasonal reversal of winds.
Southwest Monsoon (June–September):
1. Arabian Sea branch: Hits Kerala June 1 → moves up western coast → heavy rain on Western Ghats 2. Bay of Bengal branch: Hits Odisha/Bengal → moves westward and northward
- Caused by low pressure over Thar Desert (intense summer heating)
- Two branches:
- Tamil Nadu is in the rain shadow of Western Ghats — Arabian Sea branch gives little rain
- Annual rainfall: Chennai ~1,270 mm, most Tamil Nadu 600–900 mm from northeast monsoon
Northeast Monsoon (October–December):
- Also called "Retreating monsoon" or "Winter monsoon"
- Winds blow from northeast (land) → Bay of Bengal → picks up moisture → hits Tamil Nadu and southeast Andhra Pradesh
- Tamil Nadu gets 60% of annual rainfall from northeast monsoon — unique in India
- Chennai receives ~600 mm from northeast monsoon alone
- 2015 Chennai floods — heaviest northeast monsoon rainfall in 100 years (November 2015)
Western Disturbances:
- Extratropical cyclones originating in the Mediterranean → bring winter rain to Northwest India (Punjab, Haryana, HP, J&K) from December to March
- Important for Rabi crop (wheat) in north India
Seasonal Variation in Tamil Nadu
| Season | Months | Rainfall Source | Impact |
|---|---|---|---|
| Summer | March–May | None significant | Extreme heat (40–43°C in interior) |
| Southwest Monsoon | June–September | Minimal (rain shadow) | 30–40% of annual rainfall |
| Northeast Monsoon | October–December | Bay of Bengal | 50–60% of annual rainfall |
| Winter | January–February | Western disturbances (minimal) | Cool, dry weather |
Cyclones and Tamil Nadu
Tamil Nadu's long coastline (1,076 km) is vulnerable to Bay of Bengal cyclones, primarily during October–December.
- Cyclone season aligns with the northeast monsoon
- Recent major cyclones: Vardah (2016, Chennai), Gaja (2018, Nagapattinam-Thanjavur), Nivar (2020, Puducherry), Michaung (2023, Chennai coast)
- IMD issues colour-coded cyclone warnings: Yellow → Orange → Red
- District Collector leads cyclone evacuation under DDMA
Board Exam Tips
- Mettur Dam (Stanley Reservoir) opening date: June 12 — for Kuruvai season paddy cultivation. Frequently asked.
- Northeast monsoon = Tamil Nadu's primary monsoon. This is unique — ask candidates why, and the rain shadow answer impresses.
- Narmada and Tapti flow westward — the only major Peninsular rivers that do. All others flow east.
- Hirakud Dam = longest dam in India (25.8 km, Odisha). Tehri = tallest (260 m).
- Indus Waters Treaty 1960: India gets Ravi, Beas, Sutlej. Pakistan gets Indus, Jhelum, Chenab.
- Cauvery origin: Talakaveri, Kodagu (Karnataka) — not Tamil Nadu.
- Pulicat Lake: 2nd largest brackish water lagoon. On TN-AP border.
Frequently Asked Questions
Himalayan rivers (Ganga, Brahmaputra, Indus) are perennial — fed by glacier melt and monsoon, so they flow year-round. They carry large sediment loads and form fertile deltas. Peninsular rivers (Cauvery, Krishna, Godavari, Mahanadi) are seasonal — fed mainly by monsoon rain, so they carry less water in summer. Exceptions: Narmada and Tapti flow west (unlike most peninsular rivers that flow east into Bay of Bengal).