GCSE Geography | Causes of Floods and Effects of Flooding Rivers

Geography Quiz - Flooding (Questions)

Explore how different causes of river flooding turn heavy rain into a hazard and see how geography helps explain damage, risk and protection along river valleys.

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Fascinating Fact:

Rivers may burst their banks when discharge exceeds the capacity of the channel, leading to water spreading across the floodplain.

In GCSE Geography, flooding is studied as a river-based natural hazard. You explore physical and human causes of floods, their impacts on people and the environment, and strategies used to manage flood risk.

Key Terms

Floodplain: The flat land next to a river that is naturally prone to flooding when water overflows the river banks.
Discharge: The volume of water flowing past a point in a river each second, usually measured in cubic metres per second (cumecs).
Hard engineering: Man-made structures, such as dams, embankments and flood walls, built to control the flow and level of a river.

Frequently Asked Questions (Click to see answers)

What causes river flooding in GCSE Geography?

River flooding can be caused by prolonged rainfall, intense storms, snowmelt, steep slopes, saturated ground, urbanisation that increases runoff, and deforestation which reduces interception.

What are the impacts of flooding on people and the environment?

Flooding can damage homes, roads and businesses, disrupt transport and services, and threaten lives. It can also deposit fertile silt on floodplains and create new wetland habitats.

How can flood risk be managed in GCSE case studies?

Flood risk can be managed by hard engineering, such as levees and dams, and soft engineering, like flood warnings, land-use planning, floodplain zoning and river restoration.

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How do river floods occur?

[ ]	When the volume of water in the river is more than the channel can contain
[ ]	When it rains heavily, increasing the amount of water in the river channel
[ ]	When dams release water, giving a sudden large amount of water in the river channel
[ ]	During spring melt, leading to a large amount of water suddenly entering the channel

In Britain millions of homes are required to keep up with housing needs. How does building houses increase the risk of flooding?

[ ]	Increased water consumption increases the amount of necessary drainage
[ ]	More lawns, trees and other vegetation leads to more water soaking into the ground after people water their plants
[ ]	Increased pollution leads to more rain in the immediate area
[ ]	Impermeable surfaces, better drainage and less vegetation all lead to water reaching the river channels faster

Deforestation can increase the risk of flooding. Which of these is not a way trees, vegetation and forests decrease the chances of flooding?

[ ]	The uptake and storage of water into the leaves and stems of plants removes it from the ground
[ ]	Less water gets to the river as transpiration via the leaves means water is returned to the atmosphere
[ ]	Water falls on the trees and so does not reach the ground
[ ]	River banks are made more stable by vegetation

How do impermeable rocks influence the risk of flooding?

[ ]	Impermeable rocks increase the flood risk
[ ]	Impermeable rocks decrease the flood risk
[ ]	Impermeable rocks don’t influence flood risk, but they do force rivers to rise faster
[ ]	Impermeable rocks are never associated with rivers

In Ancient Egypt they welcomed the floods each year with ceremonies and celebration. How are floods beneficial to the land either side of the river?

[ ]	The flood destroys predators of domestic animals
[ ]	The silt deposited by the flood can make the ground more fertile
[ ]	The flood removes debris from the land
[ ]	The flood drops stones and blocks on to the land which are used as building materials

In 1993 the Mississippi river overtopped its banks and flooded a huge proportion of the USA. How did hard engineering lead to this catastrophic flooding?

[ ]	Dams were built to hold back the water levels. Due to the soft geology on either side these failed. The extra pressure of the water from upstream dam failures contributed to failures further down stream
[ ]	Levees had been constructed to raise the banks, as the river bed silted these were raised and the river flowed higher than the surrounding land. When they failed the water drained across the land
[ ]	Straightening of the rivers lowered the bed level, meaning the channel was able to hold more water. The extra water created a greater flood when the banks burst
[ ]	The width of the river valley was increased, allowing more water to build up in the valley before the banks burst and the river flooded the area

Once raised the Thames Barrier stops water movement along the river. How do barriers such as this reduce the risk of flooding?

[ ]	The barrier prevents the high tide increasing the water level in the river
[ ]	The barrier holds back the outflowing river discharge
[ ]	The barrier prevents groundwater entering the river
[ ]	The barrier stops tributaries entering the main channel

Rather than putting expensive flood defences in place, why are some areas being abandoned to flooding?

[ ]	The areas abandoned are industrial areas, reducing the economic cost and risk to residential areas
[ ]	Council planning and zoning means that it is illegal to build on the floodplain. Older properties that have already been built on the flood plain do not represent a cost-effective area to protect
[ ]	Allowing rivers to flood is cheaper in the short term, but may be more expensive in the long term as it encourages flooding down river over time
[ ]	Allowing rivers to naturally flood areas that are undeveloped reduces the risks of flooding further down river. The cost of protecting the entire length of every river would be prohibitively expensive

Each year the Amazon River and several tributaries over top their banks and flood the surrounding area. Which of the following is not a positive of these seasonal floods?

[ ]	The floods deposit alluvial silt on the thin infertile soils of the rainforest floor
[ ]	The flooded areas provide a unique habitat for certain species of fish during the flood season
[ ]	Increased pollution levels in the river may lead to an increase of pollution in the flooded soils
[ ]	Seasonal pools either side of the river are flooded and the water refreshed after the drier periods

10.

Which of the following river features are not influenced or created by flooding?

[ ]	Waterfalls
[ ]	Levees
[ ]	Ox-Bow Lakes
[ ]	Flood plains

Geography Quiz - Flooding (Answers)

How do river floods occur?

[x]	When the volume of water in the river is more than the channel can contain
[ ]	When it rains heavily, increasing the amount of water in the river channel
[ ]	When dams release water, giving a sudden large amount of water in the river channel
[ ]	During spring melt, leading to a large amount of water suddenly entering the channel

The technical definition of a flood is when the water leaves the main river channel or defined edges. Whilst spring melt, dams bursting and heavy rains will increase the amount of water in the river channel, many river channels can cope with this

In Britain millions of homes are required to keep up with housing needs. How does building houses increase the risk of flooding?

[ ]	Increased water consumption increases the amount of necessary drainage
[ ]	More lawns, trees and other vegetation leads to more water soaking into the ground after people water their plants
[ ]	Increased pollution leads to more rain in the immediate area
[x]	Impermeable surfaces, better drainage and less vegetation all lead to water reaching the river channels faster

Housing estates increase the amount of impermeable surfaces in the form of house roofs, concrete, tarmac, and membranes. These solid surfaces drain water into drainage systems that carry the water into the streams far quicker. Modern housing estates attempt to allow more natural drainage to increase the time it takes for water to reach the main river channel

Deforestation can increase the risk of flooding. Which of these is not a way trees, vegetation and forests decrease the chances of flooding?

[ ]	The uptake and storage of water into the leaves and stems of plants removes it from the ground
[ ]	Less water gets to the river as transpiration via the leaves means water is returned to the atmosphere
[x]	Water falls on the trees and so does not reach the ground
[ ]	River banks are made more stable by vegetation

Vegetation is one of the leading ways that water can be slowed as it passes through the drainage basin. Trees draw up the water from their roots and pass it straight into the atmosphere, or store it themselves. They also allow natural drainage through the soil rather than over land across hard packed earth

How do impermeable rocks influence the risk of flooding?

[x]	Impermeable rocks increase the flood risk
[ ]	Impermeable rocks decrease the flood risk
[ ]	Impermeable rocks don’t influence flood risk, but they do force rivers to rise faster
[ ]	Impermeable rocks are never associated with rivers

Water can't penetrate the surface of impermeable rocks. Numerous igneous and metamorphic rocks are impermeable, forcing the water to run over their surface and rapidly into the drainage system

In Ancient Egypt they welcomed the floods each year with ceremonies and celebration. How are floods beneficial to the land either side of the river?

[ ]	The flood destroys predators of domestic animals
[x]	The silt deposited by the flood can make the ground more fertile
[ ]	The flood removes debris from the land
[ ]	The flood drops stones and blocks on to the land which are used as building materials

Alluvial soils can contain organic material, but also the minerals and other nutrients that might be depleted by plant growth and rainfall

In 1993 the Mississippi river overtopped its banks and flooded a huge proportion of the USA. How did hard engineering lead to this catastrophic flooding?

[ ]	Dams were built to hold back the water levels. Due to the soft geology on either side these failed. The extra pressure of the water from upstream dam failures contributed to failures further down stream
[x]	Levees had been constructed to raise the banks, as the river bed silted these were raised and the river flowed higher than the surrounding land. When they failed the water drained across the land
[ ]	Straightening of the rivers lowered the bed level, meaning the channel was able to hold more water. The extra water created a greater flood when the banks burst
[ ]	The width of the river valley was increased, allowing more water to build up in the valley before the banks burst and the river flooded the area

The water levels were so high that 6 million acres of farm-land was flooded. The human causes of the flood include the poorly built levees, the development of unsuitable areas and large amounts of channelisation

Once raised the Thames Barrier stops water movement along the river. How do barriers such as this reduce the risk of flooding?

[x]	The barrier prevents the high tide increasing the water level in the river
[ ]	The barrier holds back the outflowing river discharge
[ ]	The barrier prevents groundwater entering the river
[ ]	The barrier stops tributaries entering the main channel

Rising sea levels and the land level falling in the south of England both put London at a high risk of flooding. The Thames Barrier is meant to hold back the sea but it has been suggested that low-lying land either side of the barrier may allow the sea to pass round it

Rather than putting expensive flood defences in place, why are some areas being abandoned to flooding?

[ ]	The areas abandoned are industrial areas, reducing the economic cost and risk to residential areas
[ ]	Council planning and zoning means that it is illegal to build on the floodplain. Older properties that have already been built on the flood plain do not represent a cost-effective area to protect
[ ]	Allowing rivers to flood is cheaper in the short term, but may be more expensive in the long term as it encourages flooding down river over time
[x]	Allowing rivers to naturally flood areas that are undeveloped reduces the risks of flooding further down river. The cost of protecting the entire length of every river would be prohibitively expensive

Flooding undeveloped areas or sparsely developed areas is a cost effective solution. Expenisve hard engineering projects often lead to more problems down stream

Each year the Amazon River and several tributaries over top their banks and flood the surrounding area. Which of the following is not a positive of these seasonal floods?

[ ]	The floods deposit alluvial silt on the thin infertile soils of the rainforest floor
[ ]	The flooded areas provide a unique habitat for certain species of fish during the flood season
[x]	Increased pollution levels in the river may lead to an increase of pollution in the flooded soils
[ ]	Seasonal pools either side of the river are flooded and the water refreshed after the drier periods

Some fish, such as discuses and other cichlids, have adapted to these yearly flooding events. Some fish live in the pools either side of the river and thousands die during the dry season. Others use the flooded plants to raise their fry before retreating water levels force them back into the main river channel.

10.

Which of the following river features are not influenced or created by flooding?

[x]	Waterfalls
[ ]	Levees
[ ]	Ox-Bow Lakes
[ ]	Flood plains

Waterfalls are created by the river channel passing over layers of soft and hard rock, rather than catastrophic flood events. Levees can form naturally as a result of the slowing down of water flow as the flood water leaves the main channel. The quantity of water in ox-bow lakes can be altered by flooding and flood plains are the area of land either side of the river channel that floods naturally

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Geography Quiz - Flooding (Questions)

Fascinating Fact:

Key Terms

Frequently Asked Questions (Click to see answers)

Try These Related Quizzes