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KS3 Geography - Raging Rivers: Floods

A look at rivers of the world and the causes and consequences of flooding in rivers.

Indus river

The Indus is one of the world's great rivers. 
From its headwaters in the Himalayas of Tibet, it flows north-west through India before turning sharply south across Pakistan. It finally discharges into the Arabian Sea, a journey of some 3,200km (2,000 miles). 
Although some of its water comes from melting Himalayan glaciers, the vast majority is dumped by the summer monsoon. As torrential rain sweeps in from the Indian Ocean, floods are triggered almost annually.

What could be the causes of Pakistan floods?

As seen in two halves of image below are the normal course (top) and flooded course(bottom) of the Indus river as seen from satellite images.

A ClimateWire investigation into the origins of the flood disaster uncovered evidence that points to a calamity caused by man, the cumulative effect of erratic weather forecast by climate change models, massive deforestation, and lax attention to infrastructure maintenance and engineering standards.
The story of the 2010 flooding in Pakistan is a warning to other vulnerable nations that experts believe will bear the brunt of the gradual shifts in climate and weather patterns expected over the coming decades. Read from following article..

Health Hazards after floods

Unsafe food

Floodwaters contain disease causing bacteria, dirt, oil, human and animal wastes, and farm and industrial chemicals. 

Contaminated drinking and washing water and poor sanitation

Flooding impairs clean water sources with pollutants and devastates sanitary toilets. Direct and indirect contact with the contaminants – whether through direct food intakes, vector insects such as flies, unclean hands, or dirty plates and utensils – result in waterborne illnesses and lifethreatening infection diseases.

Mosquitoes and animals

Prolonged rainfall and floods provide new breeding grounds – wet areas and stagnant pools – for mosquitoes and can lead to an increase in the number of mosquito-borne diseases such as malaria and dengue and West Nile fevers

Molds and mildews

Excessive exposure to molds and mildews can cause flood victims – especially those with allergies and asthma – to contract upper respiratory diseases and to trigger cold-like symptoms, e.g. sore throat, watery eyes, wheezing and dizziness

Carbon monoxide poisoning 

Post-flood carbon monoxide (CO) poisoning is reported to be a growing problem in many developed countries. CO can be found in combustion fumes, e.g. fumes generated by small gasoline engines, stoves, generators, lanterns, and gas ranges, or by burning charcoals and woods.

Other hazards when reentering and cleaning flooded homes and buildings

Besides the flood related health problems described above, flooded homes and buildings can pose other significant health hazards and risks after floodwaters recede. First of all, electrical power systems including fallen power lines can become hazardous during cleanup activities.

Mental stress and fatigue

A flood can cause both emotional and physical stress. However, various reports attribute a major health hazard of floods to mental stress or psychological distress due to exposure to extreme disaster events.

excerpt from Health risks and hazards caused by floods by Naoki Minamiguchi 

Did you know?

  • Floods are the most common and widespread of all natural disasters outside of fire
  • 90% of all presidential-declared U.S. natural disasters involve flooding
  • Communities particularly at risk are those in low lying areas, coastal areas, or downstream from large bodies of water
  • 25% of flooding occurs outside areas formally designated as being flood prone (i.e. Special Flood Hazard Areas)

above from Palm Beach County, Florida webpage

Read from this WWF report of 2007 about the World's top 10 rivers at risk - and what are the risks? The primary objective of this report is to illustrate the most menacing threats to the world’s great river basins, in order to encourage dialogue, provoke debate, and urge governments and other stakeholders to take action before it is too late.

Causes of flooding

Floods are often caused by extreme weather. Heavy rainfall causes rivers to overflow their banks. The extra water flows on to low lying areas on either side of the river.

Usually floods develop over several days. However, very heavy rainfall over a short period of time can lead to a flash flood with little or no warning. 

Pakistan flood affected areas

Flood Preparedness

Flood response in Pakistan - the Criticism

Flood basics

What is flooding?

Flooding is an overflowing of water onto land that is normally dry. It can happen during heavy rains, when ocean waves come onshore, when snow melts too fast, or when dams or levees break. Flooding may happen with only a few inches of water, or it may cover a house to the rooftop. 

What is a river flood?

A river flood occurs when water levels rise in a river due to excessive rain from tropical systems making landfall, persistent thunderstorms over the same area for extended periods of time, combined rainfall and snowmelt, or an ice jam.

What is a floodplain?

Any land area susceptible to being inundated by flood waters from any source

click on image to see larger image

Flood consequences - Pakistan

Flood damage to houses and towns is often reported in the newspapers, but what are the long term consequences of flooding for local wildlife and ecosystems? And is flooding likely to increase as the climate warms?

Watch a slideshow on Flood Control Measures

Some of the controls that can be implemented to prevent flooding 

  • Dams and Barriers - They hold back a river and manage its flow
  • Concrete Levees - Concrete embankments built alongside rivers to keep river in its course
  • Dredging - To prevent floods , the river's bed is dredged to lower it and embankments are built
  • Protecting Wetlands - The marshlands act as a reservoir for heavy rains

Flood response in Pakistan - the aid

About 1,750 people died in last year's floods in Pakistan, and up to 20 million people were affected. They started in the mountainous north and surged south, destroying 1.2m homes and damaging about 14% of Pakistan's land under cultivation.