River Landforms

River landscape characteristics

• The changes in river channel characteristics lead to alterations in the river landscape.
• Upland and lowland regions of rivers exhibit distinct landforms.
• Upland Features:
  • Waterfalls
  • Gorges
  • V-shaped valleys
  • Interlocking spurs

Waterfalls and gorges

• Waterfalls form when there's a descent in the river bed from one level to another.
• This descent often occurs due to variations in rock hardness, where hard rock overlays softer rock.
• The primary erosional processes involved are hydraulic action and abrasion.
  • Soft rock erodes more rapidly, creating an undercut beneath the hard rock, resulting in a plunge pool.
  • Subsequently, an overhang of hard rock develops, eventually collapsing over time.
  • The collapse contributes to the deepening of the plunge pool through increased abrasion.
  • The cycle repeats, causing the waterfall to retreat upstream, leaving behind a steep-sided gorge.

V-shaped valleys

• Vertical erosion is the primary force shaping the upper course of a river. It involves the downward cutting into the riverbed, gradually deepening the river channel.
• Weathering and mass movement processes contribute to the collapse of materials from the valley sides into the river, leading to the formation of a steep, V-shaped valley.

Interlocking spurs

• Meandering of the river channel begins in the upper course.
• Erosion occurs primarily on the outer side of the bends.
• In upland regions, this erosion process shapes interlocking spurs.

Lowland features

• Meanders
• Ox-bow lakes
• Floodplains
• Levees

Meanders

• In lowland regions, lateral erosion prevails.
• Meanders expand in size over time.
• The swiftest water flow, known as the thalweg, occurs on the outer side of the river bends, promoting erosion:
  • This erosion creates an undercut along the riverbank, resulting in a river cliff.
  • Subsequently, the riverbank collapses, causing the meander's edge to advance outward.
• Conversely, the slowest flow occurs on the inner side of the river bends, leading to deposition:
  • Deposits accumulate, forming a slip-off slope.
• The interplay of deposition and erosion causes the meander to migrate across the valley.

Oxbow lakes

• Meander size typically enlarges as distance downstream increases.
• Erosion along the outer bends can eventually create a meander neck.
• During floods, the river may breach the meander neck, creating a straighter path for water.
• Reduced water flow at the entry and exit points of the meander results in deposition.
• Eventually, the meander may become isolated from the main river channel, forming an oxbow lake.

Floodplains and Levees

• Floodplains are level areas of land situated on both sides of a river.
• The movement of meanders contributes to the creation of floodplains.
• Elevated discharge can result in the river overflowing its banks.
• As water spreads over the floodplain, a larger portion comes into contact with the land surface.
• Enhanced friction slows down the water's velocity, leading to gradual deposition of material across the floodplain, thereby elevating its height.
• Initially, the heaviest materials are deposited nearest to the river channel, forming natural embankments known as levees.