Floods part 1 Flashcards
What are floods?
‘Floods are overflows of large amounts of water onto land that is normally dry.’
What are the types of floods?
Coastal floods, river floods and flash floods.
Elaborate on coastal floods.
● Coastal floods occur in areas along the coast (especially low-lying coastal
land, such as river mouths)
● Coastal floods are caused by intense storms such as tropical storms and
tropical cyclones
○ Tropical cyclones are also known as typhoons and hurricanes.
● Example: The Great Tohoku Earthquake and Tsunami that hit Japan in 2011
caused a coastal flood in Miyako City
Elaborate on river floods
● River floods occur when water in the river rises and overflows its banks
● River floods occur on the floodplain, which consists of the river and the low-
lying land on either side of it
● The raised banks on both sides of the river are known as levees
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● River overflows have many possible causes
○ Snowmelt
○ Heavy rainfall
○ Dam failure
● Examples of river floods:
○ Mississippi River flood in the United States of America in 2011
○ Flood in Brisbane, Queensland, Australia, in 2011
Elaborate on flash floods
● A flash flood can be recognised by its quick rise in water level
● A flash flood takes place suddenly and lasts for a short period of time
● A flash flood can be caused by various factors
○ Heavy rainfall
○ Coastal and river floods
What are the causes of floods?
Rainfall,snow melt, storm surges and failure of man-made features.
Elaborate on rainfall
● ‘Rainfall refers to droplets of water that fall to the ground.’
● How rain is formed:
1.Water vapour in the atmosphere condenses to form water droplets
2.The water droplets form clouds
3.When the water droplets become too heavy they fall as rain
What are the characteristics of rainfall?
● The characteristics of rainfall include rainfall intensity, duration and frequency
Explain rainfall intensity
● The rate at which rain falls, measured in millimetres per hour (mm/h)
● Example: The highest recorded rainfall intensity of the day was 88.8
mm/h
Explain rainfall duration
● The duration of the rain event. How long did it rain?
● Example: 3 hours
Explain rainfall frequency
● The probability of occurrence of a certain amount of rain falling within
a certain period of time
● Example: 1-in-50-year storm in England in June 2012
•During a tropical cyclone, rainfall is of high intensity and lasts a long time
•A tropical cyclone is also known as a hurricane or typhoon
Elaborate on snowmelt
● Snowmelt is surface runoff that results from melting snow.
● How snowmelt can lead to flooding:
1.During winter, ice and snow form on th grounds and on mountains.
2.When spring arrives and the temperature rises,the ice and snow melts
3.The snowmelt flows over the land into the rivers,increasing the amount of water in the river.This causes the river to overflows its banks and flood the surrounding areas
Elaborate on storm surges
● A storm surge is a sudden rise of the sea level in which water is piled up
against a coastline beyond normal high-tide conditions.
● During a storm, strong winds push water towards the coast and create huge waves, giving rise to a storm surge.
How do storm surges cause floods?
During storms, strong winds create large waves known as storm surges
Elaborate on failure of man-made structures.
● The failure of man-made structures such as dams, levees and floodwalls can
result in floods.
Dams:
- A dam is a barrier built across a river to retain and restore water.
- When a dam fails,flooding can result
Levees:
- Levees are raised river banks which can be natural or man made
- They act as flood barriers,but can cause flooding when they fail
Floodwalls:
- Floodwalls are man-made structures made of concrete
- They act as flood barriers, but can cause flooding when they fail
