Revision: Physical World

Rivers

River Processes

1. Erosion and Transportation in the River

2. Different River Landforms along the river

Turn to Page 10-15 in Tomorrow's Geography

What does the specification say?

Rivers produce distinctive landforms in their valleys.- The change in the characteristics of a river and its valley between source and mouth.The formation of interlocking spurs, waterfalls, meanders, ox-bow lakes, flood plains, levees and deltas.Changes in characteristics such as width, discharge and gradient of the channel, and in the cross-section of the valley. Knowledge of case studies will not be required in the exam, but there are opportunities to link landforms and processes.Students will be expected to: Describe the landforms specified, and explain their formation in terms of the processes involved. Annotated diagrams of the landforms may be required.Students will need to be able to recognise the landforms specified on OS maps and in photographs.

Methods of Erosion

A river can erode material from its bed and banks in 3 main ways

Abrasion – Moving water throws particles it is carrying against the bed and banks of the river which dislodges more material Hydraulic Action - The sheer force of the water pounding into the bed and banks can dislodge material Attrition - Particles being carried downstream knock against each other, wearing each other down. This results in smaller, rounder particles as you move downstream

Methods of Transportation

Rivers transport material in 4 main ways Solution - Some minerals (particularly in limestone areas) dissolve easily in water and are not visible to the naked eye Suspension – As the speed or velocity of a river increases, it is able to pick up and carry larger and larger particles in its flow. Where particles are carried along in the flow and are not in contact with the river bed, they are said to be travelling in suspension.

Methods of Transportation

Saltation - Heavier particles may not be held in the flow all the time but may be bounced along the bed Traction - The heaviest particles are rolled along the bed. Such particles may only be moved when the river has a large volume of water in it

It’s your turn!

Using Page in Tomorrow's Geography – produce a mindmap about the different methods of Erosion and Transportation that occur in rivers Now try to draw a simple diagram to represent each process within the river

Fluvial processes create landforms. These processes are affected by specific factors.

Fluvial (River) Processes

River Structure

River Features

Rivers are eroding, transporting and depositing constantly within the drainage basin system. The river can be divided into 3 sections – Upper Course at the Source, Middle Course and Lower Course at the Mouth of the river. The river displays different characteristics at each section

Also known as ‘Torrent’ or ‘Youth’ stages

Interlocking Spurs

In the Upper Course, the river is fast flowing, but there is little water and load. The river is often called a stream and does not have the erosive power to remove the hillsides (spurs), but erodes downwards instead.

EROSION TYPE: Vertical and Headward

Upper Course

Upper Course:Interlocking

Spurs

Interlocking Spurs

River channel

Potholes

Boulders broken off by erosion that sit on the river bed create swirling eddy currents as the water flows past as the river is not strong enough yet to move the boulders by TRACTION. These eddies swirl the boulder round and erode a pothole in the river bed by ABRASION.

EROSION TYPE: Vertical

(by EDDY CURRENTS)

Upper Course: Potholes

Waterfall and Gorge 1

(OBLIQUE AERIAL VIEW)EROSION

TYPE: Vertical and Headward

Upper Course: Waterfalls & Gorges

Waterfall and Gorge 2

(PROFILE VIEW)EROSION

TYPE: Vertical and Headward

Upper Course: Waterfalls 2

Meanders

Meanders are formed because the current swings to the outside of a bend and concentrates the erosion there. Deposition occurs on the inside of the bed where there is not enough energy to carry load.

EROSION TYPE: Lateral

Also known as the ‘Mature’ stage Meanders 1

(Aerial View)

Middle Course: Meanders

Meanders 2 (Profile View / Cross

Section X - Y)

EROSION TYPE: Lateral

This cross section clearly shows the eddy current (near ’X’) formed by the velocity of the river being concentrated on the outside of the bend. These UNDERCUT the bank causing the formation of a RIVER CLIFF. On the inside (NEAR ‘Y’), a SLIP-OFF-SLOPE is formed where current is too slow to carry any load.

Middle Course: Meanders 2

Ox-Bow Lake 1

(Aerial View)

EROSION TYPE: Lateral

Ox-bow lakes are formed when two meander RIVER CLIFFS are being eroded towards each other. These will eventually meet, causing the river to then flow across the bottom of the diagram.

Middle Course: Ox-bow lake

Ox-Bow Lake 2 (Aerial View)

Middle Course: Ox-bow lake 2

Leveés and Raised Beds 1 (Front View)

DEPOSITION FEATURE: no

erosion in the Lower

Course

Leveés are formed when rivers flood. The river water overflows the banks of the river and immediately slows down due to friction with the FLOODPLAIN. This drops the larger particles first, building up a raised river bank called a LEVEÉ.

Lower Course: Levees

Leveés and Raised Beds 2 (Front View)

DEPOSITION FEATURE: no

erosion in the Lower

Course

Raised beds form in the Summer months when the river volume and energy are low and load is dropped onto the river bed. The bed raises up and the capacity of the river reduces, causing flooding in the winter. This in turn builds up the leveés and the whole process raises up the level of the river in the landscape.

Lower Course: Levees 2

Delta(Aerial View)

This deposition feature is one of the largest. When the flowing river hits the non-flowing sea, energy is suddenly lost. This causes all of the load in the river to drop in the river MOUTH. This builds up over time to create a delta – an area of land. The river divides into DISTRIBUTARIES to continue to the sea, which is now some way away from its original meeting point.

Lower Course: Deltas