Key terms

CHECKLISTS

Let’s see what we have

managed to cover this half

term.

Learning objectivesTo understand landforms of fluvial erosion and deposition.

PotholesRapidsWaterfallsGorgesMeandersOxbow lakesBraidingFloodplainsLeveesDeltas

Upper course landforms

Lower course landforms

Overview

Landforms Overview• Rivers are constantly shaping the

landscape as they carry water and sediment along their courses

• Where a river has excess energy it will erode its channel creating waterfalls and gorges.

• When energy levels fall deposition will occur forming extensive floodplains

• Erosion and deposition can combine to form meanders

Can you match up the landforms and the pictures?

1. Potholes• Potholes are circular depressions in

the river bed• Process–Rock fragments are drilled into

holes/cavities by the turbulent whisking action of a river

– Erosional process = corrasion–Rock will overtime become smooth =

Abrasion

Kukdi River, Nighoj, India

Pothole and the rock fragment that

formed it

Over time, they may widen and join with other potholes to form larger potholes, and

the whole river bed is deepened.

ACTIVITY - Draw two diagrams to show the processes that cause a pothole to form

• A river flows over a variety of different rock

• Tougher rock = eroded less easily• Weaker rock = eroded quicker• This results in irregular steps in the long

profile of a river• Cause turbulent flow in a stretch of river• This is known as a rapid.

2. Rapids

Rapids form stretches of white water as the river plunges over jagged rocks and mini waterfalls to form dangerous whirlpools and fast-flowing tubes

of water

How do you think

waterfalls are formed?

Who can name and describe the formation of these landforms?

3. Waterfalls

High Force – River Tee

Watch this!• http://www.youtube.com/watch?v=jqCR-9nBgWQ• http://

www.youtube.com/watch?v=YP1J1csZaCM&feature=related

http://www.youtube.com/watch?v=jqCR-9nBgWQ

http://www.youtube.com/watch?v=jqCR-9nBgWQ

http://www.youtube.com/watch?v=YP1J1csZaCM&feature=related

http://www.youtube.com/watch?v=YP1J1csZaCM&feature=related

EXAMPLEHigh Force waterfall on the River Tees• Water plunges 20 metres over the edge of a

tough outcrop of dark igneous rock called dolerite• Beneath the dolerite are mainly sedimentary

rocks like limestone and shale• Sedimentary rocks erode quicker causing the

formation of a plunge pool• This undercuts the waterfall at its base causing

the overhanging dolerite to collapse• This cycle repeats• Formation of a 1.5km gorge.

http://maps.google.co.uk/maps?hl=en&q=river%20tees%20map&bav=on.2,or.r_gc.r_pw.r_qf.&bpcl=37189454&biw=1024&bih=648&wrapid=tlif135218804049521&ie=UTF-8&sa=N&tab=il

Waterfall Formation

ACTIVITY 2Create a story board to the formation of HIGH FORCE waterfall in the upper course of the River Tees.1. Use the 6 statements to help you do this.2. Label your diagrams with these key words

DOLERITELIMESTONE AND SHALE

UNDERCUTTING CORRASION

HYDRAULIC ACTION

1.5 km GORGE

OVERHANGING

RETREAT

PLUNGE POOL COLLASPE

20 metres

The formation of a waterfall – Example___________________________

1

2

3

4

5

6

• The water starts to undercut soft rock underneath the hard rock, creating the beginnings of a plunge pool

• Water flows over a gap in hard rock• Falling rock and the force of water also help to

create a plunge pool through erosional processes like hydraulic action and corrasion

• As the waterfall retreats it leaves a steep-sided gorge. Over thousands of years the waterfall can move several miles

• The waterfall retreats over time, with the process starting again

• The overhanging hard rock eventually falls into the water as the base of the waterfall has been undercut

1. Water flows over a gap in hard rock2. The water starts to undercut soft rock

underneath the hard rock, creating the beginnings of a plunge pool

3. The overhanging hard rock eventually falls into the water as the base of the waterfall has been undercut

4. Falling rock and the force of water also help to create a plunge pool through erosional processes like hydraulic action and corrasion

5. The waterfall retreats over time, with the process starting again

6. As the waterfall retreats it leaves a steep-sided gorge. Over thousands of years the waterfall can move several miles

The Middle Course of the River

The Middle Course• More tributaries join the River

Severn.• These increase the volume of water

in the River. Increasing the River’s Discharge.

Upper Course

Middle course

LANDFORM of the Middle/Lower CoursesFlood Plains

• During wet weather rivers increase in size.

• Sometimes rivers cannot hold all of the water flowing into them.

• The banks burst and the river floods on a flood plain.

• Therefore a flood plain is the area of broad flat land either side of the river.

The floodplain creates U shaped valleys in the middle course.

FLOODPLAIN

5. Meanders

What is a meander?

Meanders are sweeping

bends in the river’s course

MEANDERS ARE FORMED DUE TO EROSION

AND DEPOSITION!!

Watch this!!!

http://www.bbc.co.uk/learningzone/clips/the-river-severn-upper-course/3076.html

Processes that cause a meander to form….

• When a river emerges from the upper course, it begins to ‘swing’ or meander in order to use up surplus energy

• This is because water moves in a helicoidal flow! SWIRLS!

Pool and Riffles are created due to the ‘corkscrew’ (helicoidal) like flow.

Pools and riffles often occur in meandering channels

during low flow conditions

Riffles – shallow, fast flowing water

Pools – deep, slow flowing water

Water flows faster on the outside bend, due to centrifugal force. This fast flowing water is called the THALWEG.This causes LATERAL EROSION through ABRASION. This creates a RIVER CLIFF.

Water flows much slower on the inside bend as the river lacks energy to carry its load. This causes DEPOSITION. This creates a slip off slope.

A

B

Processes AND features of a meander

Draw a plan view

of a meander

Can you label the correct processes and landforms

of a meander?

What is a cross

section?

Cross Section From A to B

Outside-The volume and velocity of the river are higher

Information on the outside of the

meander…

The water has more energy to transport its load

Material is carried in SUSPENSIONThe force of the water ERODES and UNDERCUTS the river bank by ABRASION

UNDERCUT

This feature is called a River Cliff

Fastest flowing water is called the

THALWEG

A - outside

B - inside

On the inside of a meander….

The river is shallow and slow flowingThe river

lacks the energy to carry its load

Material is therefore deposited

This feature is called a POINT BAR

A - outside

B - inside

Cross Section From A to B

Processes creating meanders…

LATERAL EROSIONOn the outside of a bend

DEPOSITIONOn the inside of a bend

6. Oxbow Lakes

Lateral erosion on outer bend

Continued erosion results in the narrowing of the neck of the meanderThe two outer bends

meet .The river takes the shortest route. Deposition occurs in slack water.The river cuts the most efficient course. It cuts off the former bend, leaving an oxbow lake

PREP• Create a A3 summary sheet of

landforms of rivers as they move downstream

• UPPER, MIDDLE AND LOWER COURSE

• Use as many key words around the diagrams as possible!

6. Formation of a Oxbow Lake

Cross Section of a meander From A to B

The Lower Course landforms

= an extensive flat area of land on either side of the river which periodically becomes flooded.

• Mostly in lowland areas, where they can be several kilometres wide

• Often used for farming as the silt that is deposited there is very fertile

7. Floodplains

Formation of floodplains– Every time the river floods it deposits a fresh

layer of silt on top of the existing floodplain– The width of the floodplain depends upon the

amount of meandering of the river– If lateral erosion is high at the apex of each

bend the river will meander across the floodplain and cut into the bluff (valley edge)

– This widens the valley and extends the floodplain.

ACTIVITYCopy diagram 1.52 page 38 in your

books underneath your notes.

8. Levees

= when the river’s banks become raised.Formation of Levees• During high flow conditions – due to high rain fall

or snow melt rivers are unable to contain the increased volume of water flowing into it.

• Water flows over banks• Coarse, larger and heavier sediment is deposited

on top of the banks. WHY? – as the velocity of the river is slower here.

• Coarse sediment traps smaller sediment • Banks become raised.

8. Levees

ACTIVITY Draw three labelled diagrams is illustrate the

formation of natural levees.

9. Braiding What is it?

= when a river becomes sub-divided into many separate channels.Why?• River is overloaded with sediment that it is

unable to carry• Sediment is dumped• Forms islands in the middle of the river• Smaller channels are made around the island

– steepening the gradient and increasing efficiency.

9. Braiding

Braiding is common in rivers where the load is large e.g. at the snouts of a glacier

OR fluctuating discharge e.g. semi arid areas

• They occur at the mouth of a river• A river rapidly loses energy when entering the

sea or a lake• Sand, silt and clay are deposited in a fan shape• Overtime there is a build up of material – creates

new land called a delta.

• Deposition rate exceeds the rate of removal by the sea. This can happen when;1. When the sediment load is large2. Weak currents or a small tidal range

10. Deltas

• Often delta is split into separate channels = distributaries

• Two main types of delta;

1. Arcuate delta

=gently curved

E.g. River Nile

2. Birds foot = deposition along the edges of several distributaries

E.g. Mississippi

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