Landforms & channel types along a river's course

A river runs from source along its course to the mouth of the river

What is a river's course?     Different stages of a river

What is the mouth of the river?     Where the river gets to the sea

What is the source of a river?     The start of a river

There are 4 main parts to a river's course:

- Upper course

- Middle course

- Lower course

- Mouth

Landforms are found at different stages of a river's course:

Upper course (steep v-shape downward erosion):

- Rapids

- V-shaped valley

- Waterfalls

- Interlocking Spurs

Middle course (u-shaped lateral erosion):

- Meanders

- U-shaped valley

- Oxbow lakes

Lower course (open/wide u-shape lateral erosion & deposition):

- Wide Floodplains

- Estuaries

- Levees

- Deltas

Landforms are produced by erosion, transport & deposition of rivers

KEY River landforms:

- Braided channels

- Rapids & Waterfalls

- Meanders & Oxbow lakes

- Floodplains

- Levees

- Deltas

Landforms are made by natural processes and can be seen on Earth's surface (e.g. meanders)

Braided channels

Braiding occurs when a river does not have the capacity to transport it's load in a single channel so deposits it in short term, temporary bars (eyots) or long term vegetated islands

A river may lose its capacity when:

- Discharge is reduced (e.g. Following a period of low rainfall)

- When they are shallow areas in river

Banks are easily erodible meaning river is heavily laden with sediment

Example of Braided River:     Brahmaputra River, Bangladesh

- A very large braided river

- Sediment is deposited during snowmelt from the Himalayas in the spring time, which is then shaped into eyots & during remainder of the year

Waterfalls

Waterfall = cascade of water falling from a height, formed when river falls off precipice/steep incline

- Waterfalls occur when river flows over rocks of differing resistance

- Harder more resistant rocks resist erosion but soft less resistant rocks erode quickly (differential erosion)

Mini case study:     High Force, River Tees, UK

- Located on River Tees in the UK

- 20m in height

- Formed where River Tees crosses whin sill (a hard layer of rock)

- Underlying the whin sill is a layer of carboniferous limestone (a softer rock) which is easily worn away by waterfall

- As limestone is eroded the whin sill is left overhanging the waterfall.

- Overhang eventually collapses

- As this process repeats, waterfall takes shape & retreats leaving a narrow, deep gorge in front of it.

Gorges

Gorge = narrow & deep section of a river valley with vertical/near-vertical valley sides

- Gorges are most commonly formed as a result of waterfall retreat (e.g. the 700m gorge in front of High Force waterfall, UK)

They can also be formed by:

- Movement and melting of glaciers which cut deep Valleys in the earth's surface

- Surface runoff over limestone during Ice Age (water within limestone froze, making it impermeable)

- During spring snowmelt, water remains over impermeable limestone, forming a gorge (e.g. Cheddar Gorge)

Meanders

Meander…