geoplanet

River Processes & Landscapes

 

 

 

 

 

River Processes & Landscapes:

Rivers are channels of water that drain the land’s surface. They erode, transport and deposit materials, creating steep valleys and wide floodplains. As river’s cut into the landscape they expose bedrock, leading to further change through weathering and mass movement.

 

 

 

 

 

 

 

 

 

 

 

 

 

• Watershed – The high ground separating one river basin from another

• Main River Channel – The river’s main ‘flow’

• Confluence – The point where two rivers meet

• Mouth – The point where the river enters the sea

• Drainage Basin – The area of land drained by river

• Source – The place where a river begins

• Course – The route the river takes to the sea

• Discharge – The volume of water that flows through the river

• Gradient – The steepness of the rivers slope

• Velocity – The speed of the water in a given direction

• Depth –The distance from the top or surface of the water to the bottom

• Width – The extent of the river from side to side

 

Long Profile of a River:

1) Valley has a narrow floor and steep sides (Youthful Stage).

2) Valley has a wider floor and the sides are gently sloping (Mature Stage).

3) Valley has a wide, flat floor and gentle sides (Old Stage).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Upper Course:

 

1) The river erodes vertically into the bed through Corrosion and Hydraulic Action.

2) Via Physical weathering, (freeze-thaw), the channel sides are weakened and loosened.

3) Mass movement (e.g. slumping) causes the loosened material to fall into the river channel.

4) The river transport’s this new material downstream through traction and saltation.

 

 

 

 

 

 

 

 

 

 

 

 

The Middle Course:

As the river reaches the middle of its course it erodes laterally creating meanders and floodplains. The force that pushes the river towards the outwards of the bank is called the centri-fugal. Furthermore, via Helicordial Flow, material from one meander is transported to the next beach’s meander.

Lower Course:

Ox-bow lakes are formed when meanders have looped around due to lateral erosion. Erosion cuts through the narrow meander neck whilst deposition blocks off the entrance to the old meander, separating the ox-bow lake from the river. Levees form during times of flood. As the river leaves its channel there is a sudden loss of energy, resulting in the river depositing much of its load immediately next to the main channel. Overtime this deposition builds up creating a natural embankment called a levee.

 

Floodplain:

In a river’s middle course lateral erosion causes the river’s meanders to migrate. As the river erodes and deposits is creates an area of flat land, known as a floodplain. When a river floods, water inundates this flat area and deposits a covering of silt. Over time thick layers of silt can build-up leading to the creation of alluvium soil. As the river moves towards its mouth, it meanders more and more and the floodplain becomes larger and larger.

Waterfall Formation:

Waterfalls occur when there is a sudden drop in the river. This happens as a river crosses bands of soft and hard rock whereby the softer rock erodes away and there is an overhang of hard rock left. The overhang of the hard rock eventually weakens and due to erosion collapses into the plunge pool. Over time a gorge is formed as the waterfall retreats upstream due to erosional processes.