Transcript Flooding and Flood Prevention - Mr. Scotts Website

Pgs 72-79
Learning Objective and Learning
Outcomes
 Learning Objective: To understand the causes, effects
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and management of river flooding
Learning Outcomes: To know what causes rivers to
flood
To understand the effects of river flooding
To understand how the effects of river flooding can be
predicted and prevented
To compare the advantages and disadvantages of river
defence techniques
When does flooding occur?
 Flooding occurs when the level of a
river gets so high that it spills over its
banks
Waikato River (NZ) after flooding
Physical Factors
 Prolonged Rainfall: after lots of rain, the soil becomes saturated so any
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more rainfall cant infiltrate which increases runoff into rivers. The river
then discharges quicker which causes a flood
Relief: how the height of the land changes. Water flows faster on steep
slopes so a steep sided valley will allow water to run down into a river
faster
Heavy rainfall: increased runoff, which increases discharge
Snowmelt: when snow/ice melts it means alot of water goes into a river
in a short space of time
Geology: certain types of rocks (permeable e.g. limestone) absorb water
rather than letting it run over the surface but if there is impermeable
rocks e.g. clay water flows over the surface faster meaning more runoff
and a higher flood risk
Make sure you can identify these factors with the assistance of Fig 23
pg 73
Human Factors
 Deforestation: trees stop rainwater hitting the ground
directly and they also absorb rain from the ground via
their roots. By cutting down trees more water reaches
rivers which increases discharge
 Building Construction: often made from impermeable
materials like concrete and also surrounded by
surfaces like tarmac which are also impermeable.
These surfaces increase runoff which means the water
gets to drains faster and then to rivers faster increasing
discharge
Effects of Deforestation/Building
Construction
Serious Impacts of Flooding
 Floods have many impacts, but the most serious is that
people are killed by flood waters, buildings are damaged or
destroyed and jobs are lost because of damage to buildings
and equipment
 The effects of flooding are worse in poorer countries than
richer countries because there’s less money to spend on
flood protection and to help people after a flood. Also
more people live/work in areas that are likely to flood and
poorer transport links mean its harder to get help to these
places
 Think of one rich country that was badly affected by
flooding in the last ten years (hint, caused by a hurricane)
Effects of flooding on people and
the environment
 Using figure 24 pgs 74-75 use each flood listed and in
your book write 2/3 bullet points about each flood. See
if you can see any similarities from flood to flood
Prediction and Prevention of
Flooding
 2.1 million properties a year in UK at risk from
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flooding, this number keeps increasing
50% of these are from flooded rivers
Number of ways these effects can be reduced
Met Office predicts flooding and broadcasts this to the
public via internet, tv, newspapers etc
Environment Agency also has a website which has a
system of warning codes (copy these from Fig 27 on pg
57)
The aim is to reduce the effects of a flood before the
flood strikes
Planning and building design
 Local Authority has to give permission before a house
is built, in flood prone areas this wont be granted
unless a flood risk assessment is done
 By 2010 all new housing in flood prone areas has to be
flood resistant
 Different types of measures can be carried out to
protect houses depending on the level of risk
Examples of flood protecting your
home
 Move electrical sockets higher up the wall
 Replace doors with lightweight ones that can be easily
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moved upstairs
Concrete floors instead of wooden floors so they do
not rot when wet
Yacht varnish on skirting boards to protect from water
Waterproof timber instead of wood for door frames e.g
MDF
Build on stilts