River Landforms

Notes

Rivers erode (hydraulic action, abrasion, attrition, solution), transport (traction, saltation, suspension, solution) and deposit. Landforms are grouped by the three courses of a river. A river tends to reach a graded profile and is limited by its base level (usually sea level).

Upper (youthful) course: erosion dominates

V-shaped valleys, gorges and canyons (Grand Canyon, Colorado River; the Indus and Brahmaputra gorges), interlocking spurs, rapids, potholes.
Waterfalls: Angel Falls (Venezuela, the highest uninterrupted fall, about 979 m), Niagara, Victoria. In India: Kunchikal (about 455 m, Karnataka, the highest), Nohkalikai (Meghalaya), Jog (Sharavati; about 253 m) and Dudhsagar (Goa).

Middle (mature) course

Meanders (river bends) with river cliffs on the outer bank and slip-off slopes on the inner bank; wide valleys; tributaries join.

Lower (old) course: deposition dominates

Flood plains, natural levees, oxbow (cut-off) lakes, braided channels, distributaries.
Deltas: arcuate (fan-shaped: Nile, Ganga, Indus), bird's foot (Mississippi), estuarine (Narmada, Tapti, Hudson; no delta), cuspate (Tiber).
Alluvial fans and cones where a stream leaves a mountain front.

Rejuvenation: renewed erosion after uplift or fall in base level produces river terraces, incised (entrenched) meanders and knick points.

Drainage patterns

Dendritic: tree-like, on uniform rock (northern plains).
Trellis: parallel main streams with right-angle tributaries (folded Himalaya, Appalachians).
Radial: rivers flow outwards from a high point (Amarkantak, Mt Kailash).
Rectangular: along joints and faults. Parallel: on a steep slope (Western Ghats). Centripetal: flow inward to a basin (Lonar Lake). Annular and deranged patterns also occur.

Key Points

Upper course: V-valleys, gorges, waterfalls; middle: meanders; lower: floodplains, levees, oxbow lakes, deltas.
Delta types: arcuate (Nile, Ganga), bird's foot (Mississippi), estuarine (Narmada).
Rejuvenation gives terraces and incised meanders.
Drainage patterns: dendritic, trellis, radial, rectangular, parallel.
Angel Falls: highest waterfall; Kunchikal: highest in India.

MCQs

Q1. An oxbow lake is formed by:

(a) Glacial erosion
(b) A meander that is cut off from the main river
(c) Wind action
(d) Tectonic subsidence
Ans: (b).

Q2. The Mississippi delta is an example of a:

(a) Arcuate delta
(b) Bird's foot delta
(c) Cuspate delta
(d) Estuarine delta
Ans: (b).

Q3. A trellis drainage pattern develops in:

(a) Uniform rock
(b) Folded mountain regions
(c) Volcanic cones
(d) Flat coastal plains
Ans: (b).