Basic Concepts

River: A continuous body of water that flows downhill under the influence of gravity.

• Source: The origin point where a river begins, often referred to as its headwaters.
• Mouth: The location where a river empties into another large body of water, such as a larger river, sea, or ocean.

• Tributary: A smaller stream or river that feeds into a larger river. 
• Confluence: The point where two rivers meet.
• Distributary: A branch of a river that diverges from the main river and does not rejoin it. For instance, the Bhagirathi and Hooghly are distributaries of the Ganga.
• Drainage Basin: The region where all precipitation drains into a particular river or a network of rivers, also known as a catchment area.
• Watershed: The boundary that separates adjacent drainage basins; it is essentially a smaller drainage basin.

Types of Drainage Systems

Drainage systems are divided into two main categories: Sequent and Insequent systems.

• Sequent Drainage System: Rivers that follow the natural slope of the land.
• Insequent Drainage System: Rivers that do not follow the land’s natural slope and do not align with the geological structure.

Drainage Patterns

These are the various shapes formed by a river and its tributaries across the drainage basin.

• Dendritic Drainage: A tree-like pattern formed by rivers and their tributaries.
  Example: Indus, Mahanadi, Godavari.
• Trellised Drainage: Primary tributaries run parallel, and secondary ones join at right angles.
  Example: River Seine (France).
• Rectangular Drainage: Tributaries meet the main river at steep angles.
  Example: Chambal, Betwa, Ken.
• Radial Drainage: Formed when a river flows outward from a central elevated region.
  Example: South Koel, Subarnarekha, Kanchi, Karo.
• Centripetal Drainage: Streams converge towards a central depression.
  Example: Lower Chambal Basin.

• Annular/Circular Drainage: Formed by tributaries arranged in a circular shape.
  Example: Sonapet dome in Uttarakhand.
• Parallel Drainage: Tributaries run parallel to each other, following the natural slope of the land.
  Example: Rivers flowing from the Western Ghats into the Arabian Sea.
• Barbed Drainage: Tributaries flow in the opposite direction to the main river.
  Example: Arun River.
• Pinnate Drainage: Resembling the veins of a leaf, formed in narrow valleys surrounded by steep slopes.
  Example: Son and Narmada.

The Course of a River

River Course and Erosion Processes

• Corrasion (Abrasion): The action of solid materials, like boulders, carried by the river scraping and wearing down the valley walls.
• Solution (Corrosion): The dissolving of soluble materials from rocks like carbonate rocks through chemical processes.
• Hydraulic Action: The breakdown of rocks due to the direct impact of water.
• Attrition: The grinding and collision of rocks against each other, breaking them into smaller pieces.

Erosional Landforms

River Valleys: Extended depressions where rivers flow. The shape of valleys changes with the erosion stage.

• Youth Stage: Steep, narrow valleys formed by vertical erosion.
• Mature Stage: Broader, “U” shaped valleys from lateral erosion.

• Gorges: Narrow valleys with steep, rocky walls.
  Example: Kali Gandaki Gorge.
• Canyons: A type of gorge, broader at the top than at the base.
  Example: Grand Canyon in Arizona.
• Waterfalls: Sudden drops of water from a height, often creating pools below.
  Example: Niagara Falls and Victoria Falls.
• Rapids: Smaller waterfalls formed in areas where rivers flow over uneven rock resistance.
• Potholes and Plunge Pools: Circular depressions in rocky riverbeds, often forming at the base of waterfalls.
• River Terraces: Flat surfaces along the valley floor that indicate former floodplain levels.
  • Paired Terraces: Equal elevation on both sides of the river.
  • Unpaired Terraces: Found on one side of the river only, or at varying heights. 
• River Meanders: Curves in the river formed due to erosion on the outer bank and deposition on the inner bank. 

• Ox-Bow Lakes: Formed when a meander is abandoned, creating a lake in the old loop.
  Example: Kanwar Lake in Bihar.

River Transportation

Rivers transport materials in the following ways:

• Traction: Large rocks roll, slide, or bounce along the riverbed.
• Saltation: Medium-sized particles move along the riverbed in jumps.
• Suspension: Small particles like sand and silt are carried by the flowing water.
• Solution: Soluble materials dissolve in the water and are carried along.

Depositional Landforms

Alluvial Fans and Cones: Sediments deposited by rivers as they move from narrow mountain valleys to plains, forming fan- or cone-shaped deposits.

• Flood Plains: Flat, sloping land beside rivers, formed by sedimentary deposits.
• Natural Levees: Ridges formed by sediment deposition along riverbanks.
• Point Bars: Sediments deposited on the inner bank of river bends.
• Deltas: Triangular or fan-shaped features formed at river mouths due to sediment deposition.

Types of Deltas

• Arcuate Delta: Shaped like an arc.
  Example: Nile Delta, Ganga Delta.
• Bird-foot Delta: Resembling a bird’s foot.
  Example: Mississippi Delta.
• Estuarine Delta: Formed in submerged river mouths (estuaries).
  Example: Narmada and Tapi deltas.
• Cuspate Delta: Formed where sediment collisions create uneven distribution.
  Example: Tiber River Delta.