Fluvial Landforms

Fluvial Landforms

1. Erosional

   • V-shaped Valleys
     • Depends on 3 factors: Climate, geology and vegetation
     • Consequently forms interlocking spurs
     • Usually form upstream in steep sided valleys
   • Rapids
     • Forms where there is a sudden increase in the slope of the channel, or where a river flows over a series of harder bands of rock
     • Turbulence further erodes the soft rock between hard rock bands and exaggerates the rapids
   • Waterfall
     • Rapid changes in the gradient of the river cause waterfalls
     • Most commonly form where the river flows over a band of harder rock and then falls onto a softer rock, thus eroding faster through the softer layer.

2. Depositional

   • Floodplains
     • When a river's maximum water capacity is overcome it floods and the excess water flows onto surrounding land.
     • When this floodwater receeds it deposits it's load which increase the height and fertility of the land
     • As more floods occur over time the alluvium builds up wide, flat plains either side of the river - this are the floodplains
   • Levees
     • During flooding the larger load is deposited first, this builds up the river sides and creates natural embankments, or levees
     • Over time this material builds up and acts as a natural flood defence
   • Braiding
     • When a river slows and material is deposited it can build up in certain areas, this goes on over time until the river has developed small islands within it's channel
     • As the river flows around these landforms it looks similar to braided hair, hence the name
   • Deltas
     • As a river slows near a body of still water it deposits much of its load, this material builds up in the river channel until it forces the existing water out
     • This water then begins eroding new channels and overtime the process repeats many times.
     • Eventually the distinctive delta form appears as the river splits into many distributaries as it has neared the body of still water.
       • The 4 main delta types are: cuspate (singular channel), arcuate (deposition dome), bird's foot (deposition following the channels out), and estuarine (deposition either side of the single inland channel)
   • Meanders
     • As a river undergoes more lateral erosion downstream and experiences turbulence in the river channel it begins to bend the river into curves
     • These bends, over time, are eroded more and more until they become prominent land features
   • Oxbow Lakes
     • The resulting landform when a river cuts through the neck of the meander and blocks off the previous meander bend

3. Rejuvenation is the process by which the river attempts to maintain an even, graded long profile

   • As the channel gradient changes downstream these erosion features will form to revert it to its most efficient grade
   • The points at which the profile experiences dramatic drops, or rises, are called knickpoints
   • The river's profile changes because of two factors: isostatic change (the land rising relative to the sea), or eustatic change (the sea level falling)