Maarg Manthan · Topic 5.5

Fluvial Landforms and Drainage Patterns

Geography › Rocks, Erosion and Landforms · Topic 5.5

Fluvial landforms are shaped by running water. In its upper course a river cuts V-shaped valleys, gorges and waterfalls, in its middle course it forms meanders and floodplains, and in its lower course it builds levees, oxbow lakes and deltas. Drainage patterns, the arrangement of streams, such as dendritic, trellis, radial and rectangular, reflect the rock structure and slope of the land.

5 min read · UPSC Prelims · Geography · Rocks, Erosion and Landforms

At a Glance

Upper course V-valley, gorge, rapids, waterfall
Middle course Meanders, floodplain, terraces
Lower course Levees, oxbow lakes, delta
Delta types Arcuate, bird-foot, estuarine, cuspate
Patterns Dendritic, trellis, radial, rectangular, centripetal
Exam link UPSC Prelims, Geography: Rocks, Erosion and Landforms

Where Does It Fit?

This is the fifth topic of the category on rocks, erosion and landforms. The previous topic dealt with the loss of soil by water and wind, and this one describes the landforms made by rivers. The next topic covers karst landforms and the cycle of erosion. Previous topic: Soil Erosion – Water and Wind Erosion. Next topic: Karst Landforms and the Cycle of Erosion.

How Do Rivers Shape the Land?

In short: a river erodes in the hills, carries material through the plains and deposits it near the sea.

Running water is the most important agent of erosion and deposition on land. A river does three jobs: it erodes by hydraulic action, abrasion, attrition and solution, transports its load by traction, saltation, suspension and solution, and deposits it when its speed falls. The long profile of a river, from source to mouth, is steep at the top and gentle at the bottom, and three courses are recognised, each with typical fluvial landforms. The fluvial processes are part of the denudation described in Exogenic Movements, Denudation and Weathering.

What Landforms Are Typical of Each Course?

Course	Process	Landforms
Upper (youthful)	Vertical erosion; steep gradient, fast flow	V-shaped valleys, gorges and canyons, interlocking spurs, rapids, waterfalls and plunge pools, potholes
Middle (mature)	Lateral erosion along with some deposition	Meanders, wider valleys, floodplains, river terraces
Lower (old)	Deposition dominates; gentle gradient	Natural levees, oxbow lakes, braided channels, deltas, estuaries

Waterfalls: form where a river flows over a resistant rock layer; examples include Jog (Gersoppa) Falls on the Sharavathi, Kunchikal Falls and Dudhsagar.
Gorges and canyons: deep narrow valleys; the Grand Canyon of the Colorado River in the USA and the gorge of the Indus and Brahmaputra through the Himalaya.
Meanders and oxbow lakes: in a meander the river erodes the outer bank and deposits on the inner bank; if the neck is cut through, the abandoned loop becomes an oxbow lake, as seen in the Ganga plain.
Floodplains and levees: deposits on the valley floor form fertile floodplains, and during floods the heavier sediments are dropped near the bank to form raised natural levees.
Alluvial fans: where a stream leaves a mountain and slows, it spreads its load in a fan-shaped deposit; the Himalayan foothill bhabar belt is formed by such fans.

What Are the Types of Deltas?

A delta is a deposit formed when a river enters a sea or lake and slows. The shape depends on the balance between river, waves and tides.

Type	Shape	Examples
Arcuate	Fan-shaped with a curved edge	Ganga-Brahmaputra, Nile, Indus, Rhine
Bird-foot	Long fingers; where the river dominates	Mississippi
Cuspate	Pointed, tooth shape; waves dominate	Tiber
Estuarine	Rivers flow in a funnel-shaped mouth, with no real delta	Narmada, Tapi, Hooghly

The Ganga-Brahmaputra delta, including the Sundarbans, is the largest delta in the world, and the Sundarbans mangroves are shared by India and Bangladesh. The eastern-flowing rivers of the Peninsula, the Mahanadi, Godavari, Krishna and Kaveri, make deltas, while the westward-flowing Narmada and Tapi, which run in rift valleys, end in estuaries, as in Divergent Boundaries and Rift Valleys.

What Are Drainage Patterns?

A drainage pattern is the arrangement of streams in an area, which is determined by the slope, the nature and structure of the rocks and the geological history. The dendritic pattern is the most common, and the others are variations that point to special structures. Studying patterns helps in interpreting maps and in finding structure.

Pattern	Description	Typical setting and example
Dendritic	Branches like a tree	Uniform rock and gentle slope; Ganga plains and many Peninsular rivers
Trellis	Main streams parallel with short tributaries at right angles	Folded mountain areas with alternating hard and soft rocks; Singhbhum, parts of the Himalaya
Rectangular	Right-angled bends	Jointed or faulted rocks; Vindhyan region
Radial	Streams flow out from a central high point	Dome or volcanic cone; Amarkantak range, source of the Narmada, Son and Mahanadi
Centripetal	Streams flow inward to a basin	Basins and depressions; Loktak lake in Manipur
Parallel	Streams run side by side	Steep, uniform slope; rivers of the Western Ghats flowing west
Annular	Ring-like	Eroded dome with alternate hard and soft layers
Deranged	Irregular, with many lakes	Recently glaciated land

As an analytical point, the delta of a river is a trade-off between sediment supply and sea action: dams reduce the silt reaching deltas and make them shrink and sink, which is a growing concern for the Ganga, Krishna and Godavari deltas, and the drainage of India is covered in Classification of Drainage Systems of India.

Why Is This Topic Important?

Landforms Frequent figure-based questions
Deltas Indian and world examples
Patterns Map interpretation

What Came Next?

The next topic describes karst landforms and the cycle of erosion. Next topic: Karst Landforms and the Cycle of Erosion.

Key People and Terms

Meander Bend of a river
Oxbow lake Cut-off meander loop
Levee Raised bank built by floods
Delta Deposit at a river mouth
Alluvial fan Fan of deposits at a mountain foot
Interlocking spurs Ridges that alternate along a valley

Exam Corner

Points to Remember

V-shaped valleys are typical of the upper course.
Oxbow lakes are cut-off meanders.
Ganga-Brahmaputra is the largest delta.
Narmada and Tapi form estuaries.
Radial pattern: Amarkantak.

Do Not Confuse With

Levee and terrace Raised bank by flooding versus old floodplain step
Delta and estuary Deposit land versus drowned mouth
Trellis and rectangular Folded versus jointed rocks

Memory Hook

Hills cut V, plains bend and flood, sea builds delta; branches, trellis, spokes.

Mains Angle

Questions ask for river landforms and drainage patterns. These points add depth.

Courses Erosion upstream, deposition downstream
Deltas Shape depends on river and sea
Patterns Reflect structure

A Question You May Face

An original practice question, not a past paper question.

“Describe the erosional and depositional landforms made by rivers in their different courses.”

How to Answer

Three courses Upper, middle, lower.
Erosional Valley, gorge, falls.
Depositional Meander, levee, delta.
Examples Ganga and Narmada.

GS Relevance

Prelims: river landforms, delta types, drainage patterns. GS Paper 1: geomorphology.

Frequently Asked Questions

What are fluvial landforms?

Fluvial landforms are landforms made by running water. Erosional ones include V-shaped valleys, gorges, waterfalls and potholes, mostly in the upper course, while depositional ones include meanders, floodplains, levees, oxbow lakes, alluvial fans and deltas.

How is an oxbow lake formed?

An oxbow lake forms when a river meander becomes so curved that the neck between two bends is cut through during a flood. The river takes the shorter path, the loop is sealed off by deposits, and it remains as a crescent-shaped lake.

What are the types of deltas?

The main types of deltas are arcuate, fan-shaped with a curved edge, as in the Ganga and Nile; bird-foot, as in the Mississippi; and cuspate, as in the Tiber. Rivers such as the Narmada and Tapi form estuaries and not deltas.

What is a drainage pattern?

A drainage pattern is the arrangement of the streams in an area, controlled by slope, rock structure and geological history. Common patterns are dendritic, trellis, rectangular, radial, centripetal, parallel and annular, each indicating a particular type of land.

Which is the largest delta in the world?

The Ganga-Brahmaputra delta, in India and Bangladesh, is the largest delta in the world. It includes the Sundarbans, the largest mangrove forest in the world, and it is an arcuate or fan-shaped delta formed by the sediments of the two great rivers.

PYQ Practice — Statement Analysis

1 V-shaped valleys are formed in the upper course of a river.

True

Vertical erosion dominates there.

2 The Narmada and Tapi form large deltas.

False

They form estuaries.

3 A radial drainage pattern is seen around the Amarkantak range.