The middle course of the river

Learning objectiveTo be able to explain the characteristics of the middle course of the river

To be able to able landforms created in the middle course

The BIG QuestionWhy does the middle course have meanders?

C-D Must be able to describe the process that leads to the formation of meanders.

A*-B Must be able to explain the process that leads to the formation of river meanders.

What is the middle course like?

http://www.youtube.com/watch?v=_jOFjaLO98I

• What are the characteristics?

• What landforms are created?

How is material transported downstream?

Saltation

Solution

Traction

Suspension

Boulders and pebbles are rolled along the river bed at times of high discharge.

Sand sized particles are bounced along the river bed by the flow of water.

Fine clay and sand particles are carried along within the water even at low discharges.

Some minerals dissolve in water such as calcium carbonate. This requires very little energy.

How is material transported downstream?

The River Conwy has deposited material in this section of its course. Suggest reasons why this has happened.

Deposition

Water in a meander bendWater in a meander does not all travel at the same speed. The fastest and most powerful water travels around the outside of the bend.

Think about being in the back or a car when going round the corner…

Or being on a rollercoaster and being thrown to one side of the carriage.

When this happens in a river it starts to develop this bending pattern.The key players in this pattern developing are e______, t_________ and deposition.

Meander = a bend in a river

Water is pushed to the outer bend . This reduces friction with the bed and banks. So the river has more energy for transporting material which can erode the outside bank via abrasion.

Meanders

As the course of a river approaches its middle stages it flows over flatter land. Lateral erosion dominates as the river swings in large bends known as meanders. Meanders constantly change their shape and position.

TASK 1: Draw a river. Make sure it has bends it in like this one:

TASK 2: Using a different colour mark on your river the route of the fastest water.

Where the red line hits the banks – it erodes material. In the areas of the river the water is travelling slower, the water has less energy and so deposits the erodedmaterial.

Deposition

Erosion

TASK 2: Add to your diagram where deposition and erosion are taking place

Erosion

Deposition

= Erosion

= Deposition

A cross section through a meander

Cross section of a meander

Meander bend on the River Conwy

A B

Explain why there is more deposition at ‘A’ rather than at ‘B’ (3)

A cross section through a meander