What affects a river’s discharge?
27th April 2015
U: how a flood hydrograph can show how a river responds to a rainstorm
K: Revise the landforms of a river
The 3 main processes in a river are: Erosion, transportation and deposition.
Landforms are the features produced as a result of these processes.
Landforms
Interlocking Meanders, oxbow
spurs, Waterfalls lakes, flood plain
and gorges
Levees and
deltas
You have 1 minute to….
1. Write a definition of the term discharge
2. Write down the calculations – how do you work out the discharge of a river?
What’s the
connection?
How?
How?
Factors affecting discharge
How?
How?
How?
What is a flood hydrograph?
A flood or storm hydrograph is a graph
showing how a river responds to a particular
storm. It shows rainfall and discharge.
Key Terms Check:
Discharge - this is the amount of water
in a river at any given point and time.
Discharge is measured in cumecs
(cubic metres per second)
Velocity - speed of a river (measured
in metres per second)
Hydrograph - a graph showing
changes in river discharge over time in
response to a rainfall event.
Lag time - the time taken between
peak rainfall and peak discharge
Rising Limb - shows the increase in
discharge on a hydrograph
Falling Limb - shows the return of
discharge to normal / base flow on a
hydrograph
Peak Rainfall - maximum rainfall
(mm)
Peak Discharge - maximum
discharge (cumecs
Now have a go at the PPQ – June 2010
Mark scheme
INSERT
The 3 main processes in a river are: Erosion, transportation and deposition. Landforms are the features produced as a result of
these processes.
Landforms
Interlocking spurs,
Waterfalls and gorges
Landforms of the upper course:
Interlocking spurs are caused by erosion
Meanders, oxbow
lakes, flood plain
Levees and deltas
• In its upper stage the river erodes
vertically rather than laterally.
• Interlocking spurs are ridges produced
when a river in the upper stage twists
and turns round obstacles of hard rock
along its downward pathway.
Define and match up the four processes of erosion:
Hydraulic action
The force of the water hitting the bed and banks of the river.
Corrasion (or abrasion)
Attrition
Corrosion
The bedload pebbles and sand are carried along and rub
against the bed and banks of the river wearing them away.
The load collides and breaks itself up into smaller
pieces.
River water dissolves some types of rock e.g.
chalk and limestone
Match up the correct processes of transportation:
1.Saltation
P. Large boulders are pushed along the river bed
by the force of the water
2. Suspension
K. Pebble sized particles are bounced along the
river bed by the force of the water
3. Traction
x. Soluble materials dissolve in water and are
carried along
4. Solution
a. Small particles like silt and clay are carried
along in the water
The formation of a Gorge
Explain how a waterfall is formed (4) or Draw a diagram - INSERT & M/scheme
Use an annotated diagram or diagrams in your answer
Now mark your own answer:
• A fault in the geology exposes layers of hard and soft rock (1).
• Water pouring over the drop causes erosion of the softer underlying rock
(1) by hydraulic action and corrasion (1).
• This leads to the development of a plunge pool (1).
• harder rock eventually collapses into plunge pool (1)
• overtime the waterfall retreats towards the source forming a gorge (1).
A = Floodplain (1), relatively flat area (1),
in mid/lower course of rivers (1).
B = Meander (1), sequence of bends on
river (1), that move over time across/down
the floodplain (1).
Middle course - How do meanders form?
A
B
Draw and label the x-section A – B. Use the revision book P.44 to help you.
Key words: Erosion, deposition, Slip off slope, River Cliff, lateral erosion,
Abrasion, slow velocity, friction, fast flowing, efficiency, deep, shallow
Explain the formation of a meander ( 4 marks)
Channel flow is directed towards one side of the river and erosion occurs
forming river cliff (1)
Slower flowing water passes around the inside of the channel (1)
and deposition occurs forming a slip-off slope(1).
Meander migrates in direction of outside
bend (1)
How do Oxbow lakes form?
Now try a PPQ Mark scheme
Lower course – Flood plains and Levees
Use the revision book
P.45 and AQA P.101 to
complete activity 2
P.101
How can we manage river flooding?
29th April 2015
U: the causes and effects of flooding
K: Learn the different types of hard and soft engineering strategies
Review of homework PPQ:
Explain how the demand for water is met within the UK. (8 marks)
•
The North and west have a high rainfall, so good supply of water. This is
an area of water surplus (there’s a greater supply than demand)
•
The Southeast and midlands have high population densities, so high demand for water.
This is an area of water deficit (there’s a greater demand than supply)
Read the revision book P.51 ‘The UK needs to manage it’s water supply’.
Number 1 -4. Now read your answer and the mark scheme.
Which level would you award yourself? Mark /8 Why? How could you improve?
You have 1 minute to answer the question: When does a river flood?
What are the
causes of
flooding?
Use the card sort and revision book P.48 to complete the table below:
Physical causes of flooding
Human causes of flooding
Read the bottom of the revision book P.48 :
Describe how flooding is happening more often in the UK
What are the effects of flooding?
1. Effects can be classified into – Social, economic and environmental
2. Effects can also be classified:
• Primary effects – caused directly by the flood e.g. house flooding
• Secondary effects – as an indirect effect e.g. business closing down and people
lose jobs
Effects of
flooding
Social
Economic
Environmental
Cumbria
Pakistan
How can we manage flooding?
There are two types of strategies to deal with flooding:
• Soft engineering is a method of river flood management which works or
attempts to work with natural processes
• Hard engineering is a method of river flood management which involves
major construction work
1. Hard engineering – which type?
Flood relief channel
2. Soft engineering – which type?
Afforestation
3. Hard or Soft? Which type?
Dam
Landuse
zoning
5. Hard or Soft? Which type?
Channelisation
6. Hard or Soft?
Which type?
Flood
warning
4. Hard or Soft? Which type?
7. Hard or Soft? Which type?
8. Hard or Soft? Which type?
9.. Hard or Soft? Which type?