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Geography - Flooding - Coggle Diagram
Geography - Flooding
Hydrograph
Plots river discharge after a storm
Lagtime
Time between peak rainfall and peak discharge
shorter lag time = greater risk of flooding
Baseflow
Normal flow of the river
Rising limb
Increase of river discharge
Falling limb
Decrease in river discharge
Rainfall
Bars
Factors affecting hydrograph
Basin size
small
large
Soil type
impermeable
permeable
Vegetation
bare
forest
Relief
steep
gentle
Urbanisation
What is a Flood
land that is not normally underwater becomes inundated
River flood
River channel can no longer hold the amount of water flowing in it
Water overtops the banks and floods the floodplain
Causes
Long period of rainfall
winter
river levels rise
overtop bank
Flash flood
summer
thunderstorms
Boscastle
Aug 2004
Factors increasing Flood risk
Physical Factors
Precipitation
Heavy rainfall
Flash floods
River channels cannot contain volume of water
Geology
impermeable rocks don’t allow water to pass through
encourages surface runoff
increase flooding risk
Relief
Steep slopes
water flows quicker into river channels
Human Factors
Urbanisation
impermeable surfaces
tarmac
concrete
increases surface runoff
flooding more likely
Deforestation
decreases interception
water transfers into rivers quicker
Agriculture
exposed soil
surface runoff
machines compact ground
surface runoff