River Landforms (DP IB Geography)

Upper Course Landforms

Waterfalls

• Occur on horizontally bedded rocks

• Soft rock is undercut by hydraulic action and abrasion

• Due to the weight of the water and no support, the waterfall collapses and retreats upstream

• Over thousands of years, waterfalls may create a gorge

Formation of a waterfall 

Middle & Lower Course Landforms

Meanders

• Meanders are formed in rivers due to the combination of erosion and sediment deposition processes

• The river erodes the outer bank of a bend, creating a cutbank

• Deposition occurs along the inner bank, forming a point bar

• As the water flows faster along the outer bend (cutbank) it erodes the bank more, deepening the channel

• Sediment is deposited along the inner bend (point bar), causing the bank to build up

• Over time, erosional and depositional processes cause the river to develop a sinuous, meandering course

Cross-section through a meander

Floodplains

• When a river floods, a floodplain is formed

• Alluvium is a mixture of sand and gravel that is eroded on the outside of the meander

• Floodplains are built up by channel deposition

• Floodplains consist of finer materials

Levees

• A landform of deposition

• Levees are raised banks

• Coarse material is deposited near the channel

• Finer material is deposited and carried to the floodplain

• Levees are found on the edge of the river

• They are formed by repeated flooding

• When a river floods, the river’s energy is reduced

• Coarse material is dropped first and then lighter material 

• Over time, the levees build up from coarse material

Floodplain and levee formation

Deltas

• Deltas are formed when streams flow into standing bodies of water

• Rivers must carry a large amount of sediment for deltas to form

• Flocculation increases deposition

• Bioconstruction increases deposition

• Delta formation must have a rapid drop in stream velocity

• There are a variety of delta formations, such as arcuate and bird’s foot

Types of delta