Download Flood plains and Flooding

Flood plains and
Flooding
Aims
• To know and understand how
flood plains are formed
• To know and understand the
causes, effects and solutions of
a flooding event
Floodplains
Floodplain formation
Floodplains and levees are formed by deposition in times of
river flood. The river’s load is composed of different sized
particles. When a river floods it deposits the heaviest of these
particles first. The larger particles, often pebble-sized, form the
leveés. The sands, silts and clays are similarly sorted with the
sands being deposited next, then the silts and finally the
lightest clays. This deposition makes up the floodplain.
Copy out the following paragraph
and fill in the missing words:
• A _________ is an area of flat land either side of a
___________ .When a river _________ it deposits
the __________ particles first. This forms
deposited features called _________ . The lightest
materials which are sand, clay and ________are
deposited further onto the __________ .
• Missing words: silt, flood plain, river, heaviest,
flood plain, levees, floods
Flooding
What is a flood?
A flood occurs whenever a river overflows its banks
(over ‘bankfull discharge’).
However, a flood becomes a problem when the water
rises to a level where it threatens property and/or life.
bankfull
discharge
Meander
cross
section
What do you
think causes
a flood?
Draw a table like the one below
in your exercise books
Factors
Natural
Human
Reduce
floods
Increase
floods
Now look at following statements and put
them into the correct place in your table
• Heavy rainfall
• Dry, sunny weather
• Tree covered mountains
• An urban area
• Few tributaries
• Permeable rock (rocks, such as sandstone
or chalk, let water soak through them)
• Impermeable rock (rocks, such as marble
and slate, do not let water soak through
them)
• Reservoir created by a dam