Fluvial landforms are created by running water (rivers). Rivers drain nearly 68% of Earth’s land surface and act as major agents of erosion, transportation, and deposition.

I. BASIC CONCEPTS

Drainage Basin

• Area drained by a trunk river and its tributaries.
• Also called a catchment/watershed.
• Acts like a funnel collecting runoff.

Drainage Divide

• Ridge separating adjacent drainage basins.
• Prominent in youthful topography (e.g., Himalayas).

Consequent Stream

• The initial stream flows down the original slope.

II. FLUVIAL EROSION

Types of River Erosion

• Hydraulic Action – Mechanical loosening of rocks by water pressure.
• Abrasion/Corrasion – Rock fragments strike and wear the bed & banks.
• Attrition – Rock fragments collide and reduce in size.
• Solution/Corrosion – Chemical dissolution of soluble rocks.
• Downcutting – Vertical erosion (valley deepening).
• Lateral Erosion – Sideward erosion (valley widening).
• Headward Erosion – Upstream extension of the valley.

III. STAGES OF RIVER COURSE

Youth Stage

• Dominant vertical erosion.
• Deep, narrow V-shaped valleys.
• Features: Gorges, Canyons, Waterfalls, Rapids.
• Poorly developed floodplains.

Mature Stage

• Lateral erosion dominates.
• Wider valleys.
• Meanders develop.
• Floodplains begin forming.

Old Stage

• Deposition dominant.
• Extensive floodplains.
• Oxbow lakes, levees, deltas.
• Low gradient & heavy sediment load.

IV. FLUVIAL EROSIONAL LANDFORMS

1. Valleys

V-Shaped Valley

• Formed by vertical erosion.
• Narrow & deep.

Gorge (I-shaped Valley)

• Deep, narrow valley with steep sides.
• Example: Indus Gorge (Kashmir).

Canyon

• Wider at the top, step-like slopes.
• Common in horizontal sedimentary rocks.
• Example: Grand Canyon (USA).

2. Waterfalls & Rapids

• Formed due to differential erosion.
• Create plunge pools.
• Recede upstream over time.
• Large waterfalls on major rivers are called Cataracts.

3. Potholes & Plunge Pools

• Circular depressions in rocky river beds.
• Formed by rotating pebbles.
• Large ones at the waterfall base = plunge pools.

4. Interlocking Spurs

• Alternating projections of high land in V-shaped valleys.

5. River Terraces

• Old floodplain levels.
• Indicate rejuvenation.
• Paired terraces occur at the same level on both sides.

6. Incised/Entrenched Meanders

• Deeply cut meanders in hard rocks.
• Result of rejuvenation or uplift.

7. Structural Benches

• Step-like valleys.
• Due to the differential erosion of hard & soft rocks.

8. Peneplain

• Almost level surface.
• Represents near-final stage of fluvial erosion.

V. DRAINAGE PATTERNS

Dendritic

• Tree-like pattern.
• Example: Northern Plains rivers.

Trellis

• Right-angle tributaries.
• Found in folded mountains.

Radial

• Streams flow outward from the central high.
• Example: Amarkantak.

Centripetal

• Streams flow inward to the depression.
• Example: Loktak Lake.

Rectangular

• Right-angle bends due to jointed rocks.

Parallel

• On steep slopes.

Annular

• Circular pattern around domes.

VI. FLUVIAL DEPOSITION

Occurs when river velocity decreases (lower course).

VII. FLUVIAL DEPOSITIONAL LANDFORMS

1. Alluvial Fans

• Cone-shaped deposits at mountain foothills.
• Coarse sediments were deposited first.
• Steeper in arid regions.

2. Floodplains

• Formed by repeated flooding.
• Built by layers of silt & clay.
• Active & Inactive floodplains.

3. Natural Levees

• Raised embankments along river banks.
• Formed by coarse sediments during floods.
• Example: Yellow River (China’s Sorrow).

4. Meanders & Oxbow Lakes

• Erosion on the concave side → Cut bank.
• Deposition on convex side → Point bar.
• Cut-off meander forms Oxbow Lake.

5. Braided Channels

• Multiple channels separated by bars (eyots).
• Occur with high sediment load & low velocity.

6. Delta

Definition

Fan-shaped deposit at the river mouth.

Conditions

• High sediment supply.
• Shallow sea.
• Weak tides & currents.
• No large lakes upstream.

Types

• Bird’s Foot Delta – Example: Mississippi River
• Arcuate Delta – Example: Nile River
• Cuspate Delta – Example: Ebro River
• Estuarine Delta – Example: Amazon River

VIII. DOAB

• Land between two rivers.
• A common term in the Indo-Gangetic plains.