Narmada and Tapi as west-flowing rivers

Topic: Drainage System of India: Rivers, Basins and Patterns · NCERT: Class 11, Ch 3 "Drainage System"

Meaning

The Narmada and the Tapi are the two large Peninsular rivers that flow west into the Arabian Sea through rift valleys (long, narrow valleys where land sank between two faults), and they end in estuaries, not deltas. They matter because they break the usual rule that Peninsular rivers flow east, and UPSC regularly tests why they do and why they form no delta.

Explanation

Why they flow west: cause → process → result

• The general rule: the Peninsular plateau tilts gently to the east, towards the Bay of Bengal.
• So most large rivers (Mahanadi, Godavari, Krishna, Kaveri) flow east.

• They build deltas (fan-shaped piles of river sediment at the mouth).

• Cause: faulting. During the uplift of the Himalayas, the northern part of the Peninsular block bent and sank. The crust cracked into long parallel faults (breaks in the rock).

• Process: a block of land sank between two faults and formed a trough fault (the sunken block itself). The low ground of this trough slopes west.
• Result: the Narmada and the Tapi do not cut their own valleys slowly. They follow these ready-made troughs westward to the Arabian Sea. Their valleys are partly filled with old debris.
• With the Mahi, they are the only three major Peninsular rivers that run east to west. Only the Narmada and the Tapi are rift-valley rivers.

The two rift valleys

Narmada

• Source: the western flank of the Amarkantak plateau (about 1,057 m), Madhya Pradesh.
• Rift: between the Vindhyan Range to the north and the Satpura Range to the south.
• Size: about 1,312 km long. Its catchment is about 98,796 sq km. It is the largest west-flowing river of the Peninsula.
• Mouth: the Gulf of Khambhat, south of Bharuch, Gujarat. The estuary is about 27 km long.
• Tributaries: about 41 important tributaries [2]. Steep fault walls on both sides mean most tributaries are short. The basin is long and narrow, not fan-shaped.
• Left bank (Satpura side): Burhner, Banjar, Sher, Shakkar, Dudhi, Tawa, Ganjal, Chhota Tawa, Kundi, Goi, Karjan [2].

• Right bank (Vindhyan side): Gaur, Hiran, Barna, Tindoni, Kolar, Chankeshwar, Kanar, Man, Uri, Orsang [2].

• Gorge and falls: at Bhedaghat, near Jabalpur, it cuts a deep, narrow gorge (steep-sided valley) through white marble, called the Marble Rocks. Here it drops about 30 m at the Dhuandhar Falls ("smoke-mist", because the spray looks like smoke).

Tapi (Tapti)

• Source: Multai, Betul district, Madhya Pradesh, in the Satpura range, at about 752 m [3].
• Rift: between the Satpura (north) and the Ajanta–Satmala hills (south).
• Size: 724 km long, with a basin of 65,145 sq km [3]. It is the second-largest west-flowing interstate basin, after the Narmada [3].
• Mouth: an estuary near Surat, Gujarat.
• Tributaries: Purna, Girna, Panjhra, Bori, Aner, Vaghur, Arunavati, Gomai and others [2].
• Parallel rivers: the Narmada and the Tapi run side by side, separated by the Satpura.

Why estuaries, not deltas

An estuary is a wide, open river mouth where tides mix fresh river water with salty sea water. Sediment is swept away, so no new land builds up.

• Little silt: the rivers cross hard rock, so they pick up little sediment.
• Fast final stretch: the last part of their course is short and steep. The water moves fast and does not drop its load.
• Strong tides: tides in the Gulf of Khambhat scour (wash out) the mouths twice a day.
• Drowned coast: parts of the west coast are submerged (drowned by the sea), which leaves wide, open mouths.
• Result: funnel-shaped estuaries at Bharuch and Surat, not fans of new land.

Feature	Delta (Mahanadi, Godavari, Krishna, Kaveri)	Estuary (Narmada, Tapi)
Sediment load	Large, from soft alluvium	Small, from hard rock
Gradient near mouth	Gentle, long plain	Short, steep
Tides	Weak (Bay of Bengal)	Strong (Gulf of Khambhat)
Coast	Broad, emergent	Narrow, partly submerged
Landform	Fan with distributaries	Funnel-shaped open mouth

Where it occurs

• Narmada basin: mostly Madhya Pradesh, plus Gujarat and Maharashtra [2]. It runs from Amarkantak to Bharuch.
• Dams: Indira Sagar (Madhya Pradesh, upstream) and Sardar Sarovar (Gujarat).
• Narmada Water Disputes Tribunal: award in 1979. It shared the water among Gujarat, Madhya Pradesh, Maharashtra and Rajasthan. Rajasthan gets water even though it is not a basin state.
• Narmada Bachao Andolan: a people's movement against the displacement of villagers, many of them tribal.

• "Namami Devi Narmade": a Madhya Pradesh mission to clean the river and plant trees along its banks.

• Tapi basin: about 72°38′–78°17′ E and 20°05′–22°03′ N [2].

• Share: Maharashtra about 79% (about 51,504 sq km) [3], Madhya Pradesh about 15%, Gujarat about 6%.

• Dams and weirs: Ukai Dam and Kakrapar Weir (Gujarat); Hatnur Dam and Girna Dam (Maharashtra) [2].

• Estuary ports: Bharuch (Narmada) and Surat (Tapi).

Don't confuse with

• Mahi and Sabarmati: they also flow west into the Gulf of Khambhat, but they do not flow in rift valleys. The Mahi rises in the Vindhyas and crosses the Tropic of Cancer twice. The Sabarmati rises in the Aravallis.
• East-flowing Peninsular rivers (Mahanadi, Godavari, Krishna, Kaveri): they follow the eastward tilt of the plateau and build deltas. The Narmada and Tapi follow faults and form estuaries.
• Western Ghats rivers (Sharavati, Netravati, Periyar, and others): they also flow west and form estuaries, but because of the steep Ghats slope close to the coast, not faulting. They are short coastal streams, not long rift-valley rivers.
• Luni: a west-of-Aravalli river in Rajasthan that ends in the Rann of Kachchh without an open sea mouth. It is inland drainage, not a rift-valley river.

Prelims Hooks

• Rift-valley pairs: Narmada = Vindhya (north) and Satpura (south). Tapi = Satpura (north) and Ajanta–Satmala hills (south).
• Source–mouth: Narmada: Amarkantak → south of Bharuch (27 km estuary). Tapi: Multai, Betul (MP) → near Surat [3].
• Size ranking: Narmada (1,312 km, 98,796 sq km) is the largest west-flowing Peninsular river. Tapi (724 km, 65,145 sq km) is the second-largest west-flowing interstate basin [3].
• Basin share trap: the Tapi rises in Madhya Pradesh, but about 79% of its basin is in Maharashtra [3].
• Waterfall–river–state: Dhuandhar Falls – Narmada – Madhya Pradesh (Bhedaghat, Marble Rocks gorge).
• Trap statements: "The Narmada forms a delta" is false. "The Mahi is a rift-valley river" is false.

Mains Points

• Why the west-flowing rift rivers build estuaries (GS-I):
• They follow trough faults over hard rock and carry little silt.
• Their final stretch is short and steep, and strong Gulf of Khambhat tides scour their mouths on a partly submerged coast.

• So the west coast has open estuaries that favour ports (Bharuch, Surat), while the east coast has fertile deltas suited to farming.

• Big dams on rift-valley rivers (GS-III):

• Benefits: irrigation, power, and drinking water for drought-prone Saurashtra, Kachchh and Rajasthan (Sardar Sarovar, Indira Sagar, Ukai).

• Costs: displacement of mostly tribal people (Narmada Bachao Andolan), plus the need for interstate tribunals such as the NWDT award of 1979.

• Basin shape and planning:

• The narrow rift basins have short tributaries and steep walls. Good dam sites are confined to a few spots, and reservoirs flood narrow valleys where people live.
• Water sharing that covers non-basin states (Rajasthan) shows how a river basin can serve regions far beyond its own catchment.

Related concepts

• Narmada river
• Marble Rocks and Dhuandhar Falls
• Tapi river
• West-flowing rivers of the Peninsula
• Jog Falls
• Luni river
• Inland drainage

Read more

• The west-flowing rivers, rift valleys and the Luni's inland drainage