Types of floods
Coastal flood
Tropical storms
A lot of rain
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Tropical cyclones
Storm surges
Strong wind
Large waves
Huge ocean waves
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River flood
Water in the river overflows
Snowmelt (snow melting from mountains)
Heavy rainfall (too much for the river)
Dam failure (china dam always fails)
Too much
Lowlying land around the river
Flash flood
Heavy rainfall
Short period of time
Quick rise in water level
Causes of floods
Rainfall intensity
Rate at which rain falls
High rainfall intensity: a lot of rain
Rainfall duration
Duration of the rain
Rainfall frequency
Probability of occurrence of a certain amount of rain falling within a certain period of time
Surface runoff from melting snow
temperate countries
spring season, when temperature increases
Storm surge
During a storm
Strong winds push water towards the coast
High tides, water piled up against coastline beyond normal conditions
Failure of manmade structures
Example: dams and levees
Dam failure: amount of water cannot be regulated, areas downstream will be flooded
Effects of floods
SOCIAL impacts
Injuries, diseases, deaths
Waterborne diseases eg cholera
Water is contaminated
Puddles of stagnant water, mosquitoes breed dengue :(
Floods cause buildings to collapse, cause casualties
Disruption to water supply
Sewage pipes burst, sewage spills out and contaminates the water
No clean water, people cannot consume the water
No water supply to run the machines
Houses washed away
Floodwaters cause damage to
property, sweep houses away
Case study: Hurricane Katrina, nearly 1.5 million people in New Orleans were displaced or left homeless
Evacuate to shelters
ECONOMIC impacts
Damage of machines
Equipment submerged in water; cause damage to motors and electrical components
Factories cannot operate at full capacity; economic losses
Disruption to transport infrastructure
During a flood: infrastructure submerged or damaged, becomes impassable
A lot of time and money needed to repair the damaged infrastructure
Example: 2014 heavy rain in Bosnia, destroying roads and bridges, slowing down rescue and relief works
Disruption to energy supply
Affect distribution of supply of energy
Flooded road conditions trucks cannot transport gasoline from terminals to gas stations
Power lines damaged power outages
Lack of electricity: factories and anything cannot operate
Stress from loss of loved ones
Emotional distress
Example: adults who have experienced floods more likely to suffer from depression and anxiety
Loss of belongings
Items washed away by floodwater
can be things the people greatly
Even the house can hold a special meaning, rebuilding cannot bring back the memories of the house
Loss of a home stress of rebuilding a new one
Cost involved
Soil erosion
Floodwater washes the soil away,
into the water bodies
Leads to potential water pollution
Mitigation measures
Regulation (a law)
How the government plans its development of the land
Floodprone areas: reserved for Lowvalue developments like Parks and fields
Fewer casualties and less economic losses
Example: Minnesota, Minnesota river is surrounded by Parks, residential areas are further away
Elevated properties
Elevate or raise properties to a certain height
Minimum Platform Level (MPL): minimum ground level for a development
Development is protected against floods because of the elevated flood
But need to add slope and stairs, increased cost of development
Investment in infrastructure
Levees and floodwalls
Barriers against floods and protect the developments from floodwater
Levees: raised river banks
Floodwalls: manmade structures to keep out the floodwater
Example: floodprone city of Sacramento builds kilometres of levees along the Sacramento River to protect surrounding land from floods
Channel improvement
Increase the capacity of a water body to hold water
Canals and river channels can be widened and deepened to carry more water
Or straightened so water can be drained away quickly
Example: expansion of Bukit Timah canal to increase channel capacity, allowing moderate to highvalue developments LIKE NYGH to be built along the Cana
Disaster preparedness
Forecasting and warning system
Cities monitor the water levels in water bodies
Detect when the water level is exceeding the water body, about to overflow
Flood warnings will be issued to public in the event of a flood
Weather forecast: look at weather conditions, predict if a flood might occur
Evacuation drills
Plan to evacuate a large number of people in the shortest time
Purpose: raise awareness among the people, reduce panic during an actual flood as they are more prepared
Hence reduce the number of casualties as people are aware of how to evacuate
Public advisory
What to do in the event of a flood?
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