Caues And Impacts Of Flooding Flashcards
How does prolonged rainfall cause flooding?
After a long period of rain, ground becomes saturated, further rainfall can’t infiltrate, increases surface runoff, increases discharge.
How does heavy rainfall cause flooding?
Can lead to rapid surface runoff if rainfall is too intense for infiltration to occur.
Can lead to sharp rise in discharge, called a flash flood
What is another factor that can increase river discharge?
Melting snow and ice
What are the 5 physical factors that increase the risk of flooding?
Sparse vegetation/deciduous trees Impermeable ground Circular drainage basins High drainage density Steep slopes
How does sparse vegetation/deciduous trees increase the risk of flooding?
Sparse vegetation means little rainfall is intercepted, more rain reaches the ground, increases volume of water reaching the river, increases discharge
Deciduous trees have no leaves in winter, same affect as sparse vegetation - little rainfall intercepted.
How does impermeable ground increase the risk of flooding?
Clay soils and rocks such as granite and shale are impermeable - doesn’t allow infiltration of surface water, increases surface runoff, increases discharge
If ground has been baked by heat of summer or is frozen, same thing happened, can’t infiltrate, increasing runoff and discharge
How does circular drainage basins increase the risk of flooding?
Water draining into the main river channel will all arrive in a short space of time, as all points in basin are a similar distance from river, increases discharge.
How does a high drainage density increase the risk of flooding?
Drainage basins with a high drainage basin (lots of streams) drain quickly, have short lag times. Lots of water flows from streams into main river in short space of time, increasing discharge
How does steep slopes increase the risk of flooding?
If drainage basin has steep sided valleys, water will reach river channel faster as water flows more quickly down steep slope, increases discharge.
What are the 5 human factors that increase the risk of flooding?
Urbanisation Deforestation Flood management strategies Agriculture Climate change
How does urbanisation increase the risk of flooding?
Urban areas have large areas or impermeable tarmac and concrete, when it rains runoff is very rapid
Gutter and drains quickly take runoff to rivers
Both things reduce lag time and so increase discharge
How does deforestation increase the risk of flooding?
Clearing trees and plants reduces interception and evapotranspiration, increases volume of water reaching channel, increases discharge.
Deforestation leaves soil loose, soil is eroded by rainwater and carried to river, raises river bed, reduces channel capacity, takes less water for river to flood.
How do flood management strategies increase the risk of flooding?
Can end up making flooding worse, if dams fail they release a huge volume of water all at once - giving huge increase in discharge.
How does agriculture increase the risk of flooding?
Overgrazing leaves areas with less vegetation, has same affect as deforestation.
Overgrazing and ploughing also increases soil erosion.
How does climate change increase the risk of flooding?
Can increase rainfall and more storms could arise in some areas, could increase flooding
What 3 areas does flooding affect?
People
Economy
Environment
What are the social impacts of flooding?
People and animals can be killed
Floodwater is often contaminated with sewage, can lead to a lack of clean drinking water
Contaminated water can also put people at risk of diseases
Possessions an be damaged by floodwater or lost
People can be made homeless as their properties are inundated and damaged
What are the economic impacts of flooding?
Businesses often have to shut down as premises are inundated and overt supplies are affected
Rescue work and repairs are usually costly. Insurance premiums go up after floods
Unemployment levels often rise as businesses shut down because they can’t recover from the flooding
Public transport, roads and bridges can be destroyed
Crops can be destroyed, can lead to a rise in price of food
What are the negative environmental impacts of flooding?
Floodwater contaminated with sewage and rubbish can pollute rivers
River banks are eroded
What are the positive impacts of flooding?
River sediment is deposited on the flood plain, makes land more fertile.
Wetlands can be created, e.g. marshes and ponds, which are habitats for many species.
What countries have a greater social impact of flooding? (Rich/poor)
Higher in poorer countries because flood defences are poorer, people are less able to evacuate, sanitation systems aren’t as good and buildings are a poorer quality
What countries receive the biggest ABSOLUTE economic effect? (rich/poor)
Higher in richer countries as they have more high value buildings and infrastructure.
What countries receive the biggest RELATIVE economic effect? (Rich/poor)
Higher in poorer countries, the buildings and crops that are damaged are worth less money, thus affects the economy more because they have less money to recover from it
What is a flood return interval (RI)?
People can predict from records how often a flood of a certain magnitude may occur
What would the RI of a small flood be?
RI of 1-2 years
They happen more often so are more frequent
What would the RI of a huge flood be?
RI of 100 years
Floods of very large magnitude don’t happen very often - they’re not very frequent
What are the two main causes of flooding
Prolonged rainfall
Heavy rainfall
