RIVERS AS AGENTS OF EROSION, TRANSPORTATION AND DEPOSITION

You should be able to:

– Describe the changes in river characteristics as it flows downstream along its valley.

– Describe the fluvial processes of erosion, transportation and deposition.

1. Add a line to show the profile of the typical river profile.

TASK:

Complete your copy of the table

Use the information on pages 56 65 to help you.

EROSION TRANSPORTATION

DEPOSITION

Corrasion / abrasion Traction Entering the sea

Hydraulic action Saltation Overflow the banks

Corrosion Suspension Inside bend of meander

Attrition Solution Reduction in discharge (drought)

Sudden decrease in gradient (base of

waterfall)

RIVERS – PHYSICAL FEATURES

As in the lithosphere unit you are often asked to explain how physical

features are formed. Important tips:

1. Always use annotated diagrams in your answer, even when not specifically asked for them.

2. Practice drawing diagrams when you are revising.

3. Use simple line drawings – they are much quicker and easier to draw than artistic line diagrams.

4. Give plenty of detail on the processes – do not be fooled into thinking ‘this is easy – I have done this in Standard Grade’. There may be twice as many marks for a similar question at Higher(c.12 marks for one feature).

5. When given a choice of features, choose the one you can write most about.

RIVERS – PHYSICAL FEATURES

UPPER COURSE MIDDLE COURSE LOWER COURSE

Waterfalls Meanders Meanders

Pot Holes Ox-Bow Lakes

Interlocking Spurs Levee

Braiding

River Terrace

Flood Plain

NOTE:

The BOLD and underlined features are most likely to be asked. You are often given a choice.

FEATURES OF THE UPPER COURSE:

WATERFALL

1. Hard rock overlying soft rock2. Soft rock erodes more easily

(DIFFERENTIAL EROSION)3. Eventually soft rock is worn away4. This causes undercutting of hard rock5. Nothing to support the harder rock which collapses6. The process is repeated and the waterfall moves

upstream. Headward erosion7. Hydraulic action and abrasion lead to a deep plunge pool

(fully explain these processes)

Erosion processes should be mentioned throughout answerDifferential erosion is important

Answers could be in the form of a series of annotated diagrams

Diagrams should show process:1. Before2. During3. After

TASK: Make a neat copy of figure C (page 10 Connections)

Use the key to annotate your diagram

The Upper Course

Tees

Etive

North Esk

Etive

Tees

PLUNGE POOLUNDERCUTTIN

G OF SOFT ROCK

OVERHANG

WATERFALL RETREATS . .UPSTREAM . .

MEANDERS1. Development of pools (deeper flows / slower) and riffles

(shallower flows / faster) lead to initial deviance from straight river course

2. Sinuosity – tendency for river to follow a winding path3. Coriolis effect4. Erosion on the outside of the bend due to faster and

more powerful flow by hydraulic action5. Deposition on the inside of bends due to slower, less

powerful flow6. Helicoidal (corkscrew) flow removes material7. Migration of meanders downstream8. Undercut banks / river cliffs and slip-off slopes / river

beaches formed in this process

Cross section diagram and process diagramsCOPY FIGURE 3.35 ON PAGE 64

Coloured Pencils – The key is important! SQA

Middle Course - Meanders

Large Meanders

Formation of an oxbow lake

NARROW MEANDER NECK

FUTUREOX-BOW LAKE

OX-BOW LAKE

1. Small crescent shaped lake is formed from the over-development of meanders

2. River wears away outside bend of meander (lateral erosion)

3. Neck of meander narrows4. River breaks through – usually during flood conditions5. Meander is breached as river takes shorter/direct route6. Deposition of sediment on river banks results in ox-

bow lake being cut-off

LEVEE

1. Raised beaches 2. Formed by materials deposited during flooding3. Level rises over time4. Heaviest material deposited first resulting in a sloping

affect as levee moves away from river

TASK: Make a neat copy of figure 3.36Including key