River Landforms

• Formation of interlocking spurs

  • The upper corse the river erodes vertically to create a steep sides V shaped valley.
  • The river is not powerful enough to erode laterally through areas of hard rock so it winds around them
  • These areas of hard rock are called interlocking spurs
  • Interlocking spurs are fingers of land that jut into the river valley and streams and rivers are forced to flow around them in the upper course
• Waterfalls

  Occur where hard rock overlies a softer rock
• Formation of waterfalls

  1. Softer rock is eroded (By hydraulic action, abrasion and solution) more easily than the harder rock

  2. This enables the river to cut down into the channel

  3. Creates a plunge pool where the power of the water causes hydraulic action

  4. Rocks carried untie the plunge pool by the river will rub against the bed and banks of the plunge pool deepening it by abrasion

  5. Softer rock is eroded further undercutting the hard rock

  6. Overhang collapses due to gravity because it is unsupported

  7. Waterfall retreats upstream
• Gorge

  Steep sided valley created as the waterfall retreats upstream
• This process will repeat with the waterfall retreating upstream forming a gorge
• Meander

  Large bends that develop in a river during the middle course due to lateral erosion
• Formation of a meander

  1. River has a slight bend caused by weaving around an obstacle

  2. Water flows faster on the outside of the bend where it is deeper and there is less friction, and slower on the inside where it is shallower and there is more friction

  3. Outside of the bend gets eroded by hydraulic action while material is deposited on the inside of the bend

  4. Outside of the bend gets eroded more to form a river cliff and the inside of the bend builds up by deposition to form a slip off slope

  5. Bend grows into a meander

  6. Meander will continue to move downstream and change (meander migration)
• The river does not get any wider as the meander forms
• Formation of an Oxbow lake

  1. There is a meander

  2. Water flows faster on the outside of the bend than on the inside due to less friction

  3. Erosion on the outside (hydraulic action and abrasion) and deposition on the inside of the bend

  4. Erosion on the outside of the bend causes the neck of the meander to become very narrow

  5. If there is a lot of rain a flood will occur

  6. River breaks through and takes a short cut straight across the neck of the meander

  7. River now flows along the shortest course, missing out the loop

  8. Water flows faster in the middle of the new river channel because it is straighter, current is slowest at the sides which causes deposition to occur

  9. Deposition cuts off the meander, forming an oxbow lake
• Formation of a flood plain

  • Floodplains are wide, flat areas of land found either side of a river
  • They are prone to flooding
  • When a river floods, material being carried by the river is deposited on the floodplain (known as alluvium).
  • Over time this raises the height of the floodplain.
  • Floodplains are made wider due to the migration of meanders.
  • The alluvium makes the flood plains very fertile so it is good for farming.
• Formation of a levee

  • Levees are naturally raised river beds that form when a river repeatedly floods and deposits sediment
  • When a river floods over its banks, the water spreads out and slows down due to friction. As it does, the water loses energy and deposits the material it has been carrying.
  • Heaviest material is deposited first, closest to the river channel.
  • Smaller, lighter material is carried further over the floodplain.
  • Repeated flooding and deposition forms raised levees along the edges of the river channel.
• Forming of estuary

  • Estuaries are found where the mouth of a river meets the sea.
  • Estuaries are flooded daily by the tides as they rise and fall.
  • At high tide, the incoming tide meets the outflowing river and reduces its velocity.
  • This causes the river to lose energy and deposit sediment over the floor of the river valley.
  • Over time this causes layers of sediment to build up, creating wide mudflats and salt marshes which are exposed at low tide.
• Factors leading to deposition:

  • shallow water
  • at the end of the river's journey, at the river's mouth
  • when the volume of the water decreases
• • Watershed - the area of high land forming the edge of a river basin
  • Source - where a river begins
  • Mouth - where a river meets the sea
  • Confluence - the point at which two rivers meet
  • Tributary - a small river or stream that joins a larger river
  • Channel - this is where the river flows
• • Upper course - river flows downhill there is an increase in vertical erosion. The channel is shallow and narrow because there is not a lot of water in the channel.
  • Middle course - some vertical erosion but more lateral erosion. The channel is wider and deeper as a result.
  • Lower course there is a lot less erosion, with only some lateral erosion. The channel is at its widest and deepest.
• • Prolonged rainfall - if it rains for a long time, the land around a river can become saturated (it's holding as much water or moisture as can be absorbed). If there is more rainfall it cannot be soaked up, so it runs along the surface - this is known as surface run-off.
• • Heavy rainfall - if there is heavy rainfall there is less chance of it being soaked up by the soil (infiltration) so it runs off into the river. The faster the water reaches the river, the more likely it will flood.
• • Geology - permeable rocks allow water to pass through pores and cracks, whereas impermeable rocks do not. If a valley is made up of impermeable rocks, there is a higher chance of flooding as there is an increase in surface run-off.
• • Relief a steep valley is more likely to flood than a flatter valley because the rainfall will run off into the river more quickly.
• • Vegetation - trees and plants absorb water, this is known as interception. Lots of vegetation reduces flood risk. Sometimes people cut down trees (deforestation). This will increase the flood risk, as the water will not be intercepted and flow into the river.
• • Urban land use - when an area surrounding a river is built on, there is an increase in the amount of tarmac and concrete, which are impermeable surfaces. Drains and sewers take water directly to the river which increases flood risk.