Floods

Página 1

Contents

Defination of floods

Types of floods

Causes of floods

Cities that are prone to floods and why

Factors which increase risk of flooding

Impacts of floods

Mitigation measures used to prepare for floods

Defination of floods

Floods are overflows of large amounts of water onto land that is normally dry

Página 2

Types of floods

Coastal floods

River Floods

Flash floods

Coastal floods:

Occurs in areas along the coast

Can be recognised by huge waves

Caused by intense storms such as tropical storms, tropical cyclones and tsunamis

E.g. Miyako City, Japan in 2011

River floods:

Occurs when water in the river rises and overflows its banks

Can be recognised by the river banks

Caused by snowmelts ,heavy rainfall and dam failure

E.g. Mississippi river, united states in 2011

Flash floods:

Takes place suddenly and lasts for a short period of time

Can be recognised by its low water level

Caused by heavy rainfall and both river and coastal floods

Página 3

Causes of floods:

Rainfall

Snowmelt

Storm surge

Failure of man-made structures

Rainfall

Rainfall intensity (mm/h) = Total amount of Rainwater (mm) / Duration of rainfall (h)

E.g. A rain event lasts for 4.5 hours. After the rain, 45 millimeters of water was recorded. What was the rainfall intensity for this event?

45 mm/4.5 h = 10

Snowmelt

Is surface runoff that results from falling snow

Is common in temperate countries during the spring season when temperature increases

Storm surge

Is a sudden rise in the sea level in which water is pilled up against a coastline beyond normal high-tide conditions

During a storm, strong winds push water towards the coast and creates huge waves, giving rise to a storm surge

Failure of man-made structures

E.g of man made structures: Dams and levees

A dam is a barrier built across a river to retain and store water

Helps to regulate the amount of water flowing in the river

Página 4

Cities that are more prone to floods than others

Dhaka, Bangaladesh

located in the paths of monsoons

Neworlands, USA

located in the paths of monsoons

Calgary, Canada

located on mountain foothills causes floods from snowmelts

Tacloban, Philippines

located along the coast = makes it prone to coastal floods and storm surges

Newport, united kingdom

prone to floods caused by storm surges

Factors which increase the risk of flooding

Height of land above sea level

Proximity to water bodies

Permeability of surface cover

Channel capacity​​​​​​​

Página 5

Impacts of floods

Injuries, spread of diseases and loss of lives (Social)

People may be injured by objects and debris washed along by fast moving waters.

Floodwaters may cause buildings to collapse and injure or kill people.

When people are caught in a flood for too long, it can cause hypothermia with symptoms such as constant shivering, confusion and loss of coordination

Water supplies may be contaminated by chemical spills from factories and sewage

can cause and spread cholera and dysentery

stagnant water encourage water to breed, resulting in more cases of malaria and dengue

E.g. Moscow, Russia in 2012

Homelessness (Social)

Floodwaters can cause damage to property and can sweep houses away

people may have to stay in emergency shelters for a long period of time

Flooding in cities tend to affect people due to the high population densities in these area

E.g. Nearly 1.5 million people in New Orleans were homeless due to the Hurricane Katrina in 2005

Disruption to clean water supply (Social)

The supply of clean water may be disrupted due to damaged water pipes.

Sewage waters may also burst, causing sewage waters to flow and contaminate water supplies

E.g Karachi, Parkistan in 2010