Fluvial Landforms (AQA GCSE Geography)

River landscape characteristics

• The changes in river channel characteristics, lead to changes in the river landscape
• The upland and lowland areas of rivers have distinctive landforms
• Upland:
  • Waterfalls
  • Gorges
  • V-shaped valleys
  • Interlocking spurs
• These are landforms created through erosion

Waterfalls and gorges

• Waterfalls form where there is a drop in the river bed from one level to another
• This drop is often due to changes in the hardness of the rock, where hard rock overlies soft rock
• Hydraulic action and abrasion are the main erosional processes:
• • The soft rock erodes quicker, undercutting the hard rock and creating a plunge pool
  • This leads to the development of an overhang of hard rock which eventually over time, collapses 
  • The overhang falls into the plunge pool increasing abrasion and making the plunge pool deeper
  • The process then begins again and the waterfall retreats upstream leaving a steep sided gorge

Waterfall formation

V-shaped valleys 

• Vertical erosion is dominant in the upper course of the river
• This cuts down into the river bed and deepens the river channel 
• Weathering and mass movement leads to material from the valley sides collapsing into the river forming a steep v-shaped valley

Formation of a v-shaped valley

Interlocking spurs

• In the upper course of the river the channel starts to meander
• Erosion happens on the outside of the bend
• In the upland areas this forms interlocking spurs

Interlocking spurs

• Some landforms are created through a combination of erosion and deposition including:
  • Meanders
  • Ox-bow lakes

Meanders 

• In lowland areas lateral erosion is dominant
• Meanders increase in size
• The fastest water flow (thalweg) is on the outside of the river bends, leading to erosion:
  • The erosion undercuts the riverbank forming a river cliff
  • The riverbank collapses and the edge of the meander moves further out
• The slowest flow is on the inside of the river bends, leading to deposition:
  • The deposits form a slip-off slope
• Deposition on one side and erosion on the other leads to the meander migrating across the valley

Cross-section of a meander

Oxbow lakes

• With distance downstream the size of the meanders increase
• The erosion on outside bends can eventually lead to the formation of a meander neck
• At a time of the flood, the river may cut through the neck of the meander forming a straighter course for the water
• The flow of water at entry and exit from the meander will be slower, leading to deposition
• The meander becomes cut off from the main river channel, forming an oxbow lake

Oxbow lake formation

Floodplains and levees

• Floodplains are flat expanses of land on either side of the river
• The migration of meanders leads to the formation of the floodplain
• High discharge may cause the river to overflow the banks
• More of the water is in contact with the land surface as the water spreads across the floodplain
• Increased friction reduces velocity and material is deposited across the floodplain gradually increasing the floodplain height
• The heaviest material is deposited first nearest to the river channel forming natural embankments called levees

Levee and floodplain formation

Estuaries

• An estuary is where the river meets the sea
• Large deposits of sediment form mudflats and salt marshes
• These are the result of the interaction between the river and tides
  • Incoming tides bring in sediment which mixes with the sediment being carried by the river
  • When the incoming tide of salt water meets the freshwater of the river, the river velocity drops and deposition occurs
  • The deposited sediment builds up in layers to form mudflats which rise above the water surface, particularly at low tide
  • Eventually the vegetation starts to grow on the mudflats and form salt marshes

• The River Tees is located in north-east England
• It is 85 miles from source to mouth
• It flows eastwards from the source in the Pennines to the mouth where it flows into the North Sea

Map of the River Tees drainage basin

Landforms of erosion

• High Force waterfall is the highest waterfall in England
• High Force formed where dolerite, a hard igneous rock (known locally as 'whinstone') lays over a softer sedimentary rock, limestone
  • The water erodes the limestone more rapidly, undercutting the hard dolerite
  • Eventually the dolerite falls because it is unsupported and the process starts again
• The retreat of the waterfall upstream as a result of this process has left behind a steep sided gorge

Landforms of erosion and deposition

• In the middle and lower sections of the River Tees the river flows over flat, low-lying land
• Meanders form such as in the area to the south-east of Darlington

Landforms of deposition

• In the middle and lower sections floodplains and levées also form as a result of repeated flooding of the areas