1. Hydrograph data to plot
Thinking through Geog
Flooding 2
Key idea:
2. Rivers flood due to a number of physical
and human causes.
3. Flooding appears to be an increasingly
frequent event

2. Lesson objectives
• To know the terms:
Flooding, hydrograph, rising limb, falling
limb, lag time, drainage basin
• To be able to explain the factors that
cause flooding
• To know the frequency and location of
flood events in the UK over the past 20
years

3. Starter activity….
• Precipitation
• Interception
• Surface storage
• Infiltration
• Soil moisture
• Percolation
• Groundwater
• Transpiration
• Evaporation
• Surface run off
• Through flow
• Groundwater flow
• Water table

4. • Textbook page 110 task 2

5. • Discharge
• Drainage basin
• Storm hydrograph
• Flashy
• Relief
• Impermeable
• Porous
• Pervious
• Deforestation
• urbanisation

6. A flood occurs when…
…..the discharge is so great that all the
water can no longer be contained within
the channel so that the river overflows
its banks

7. So what factors affect river
discharge?

8. Factors affecting discharge
•Amount and type of rainfall • Soil
•Temperature • Land Use
• Slope
•Previous weather conditions
• Relief
•Drainage Density
•Rock Type

9. Most floods occur because of the
weather:
Amount and type of rain
• Prolonged rain – long and continuous periods of
rainfall lead to saturated ground
• With drizzle, there is time for water to infiltrate
soil and underlying rock
• Heavy rain which causes large amounts of run-off
in a short period of time
Temperature
• High temperatures lead to greater evaporation
and transpiration rates so river levels decrease
• Snow melt – in spring a sudden increase in Textbook
temperature which melts snow and ice. - In winter page 109
the water cannot seep into frozen ground
• Previous weather conditions

10. • Rock type
• Rock type determines how much water
infiltrates and how much stays on the surface.
• Relief
• Relief affects the rate at which water runs
off the land surface and into rivers. Steep
slopes give faster run off due to gravity
• Gentle slopes allow time for infiltration

11. Human activities can make the
flood risk worse …
• Building on a floodplain.
Tarmac and concrete are
impermeable which means
that more water runs off
the surface and faster.
• Deforestation reduces
interception by the trees
and so more rainwater
reaches the surface
quicker increasing rates
of surface run off

12. Your turn
• Textbook page 110 task 3
• You are to produce a double page spread around the
title ‘ The reasons river discharge fluctuates’
• In the central box give the meaning of ‘river discharge’
• Place the factors around the central title
• Add information to each factor to explain how discharge
is affected.
• Illustrate each factor with diagrams, sketches or photos.
• Your finished work should be informative, accurate,
interesting, colourful and original

13. Which are physical and which are
Plenary human factors?
What factors increase
The risk of flooding?
Building in the
drainage basin
* Very wet soil
*steep slopes
* Many tributaries * Impermeable
* Cutting * Hard dry soil rock
down trees

14. Homework….
Card sort activity
Cut out the two hydrographs – one for a
‘flashy’ river and a gentle graph
Now cut out the individual cards and place
them under the appropriate hydrograph.