S2 GE Notes - Ch 5 Floods (part 1)
- 1. EDGEFIELD SECONDARY SCHOOL SECONDARY TWO GEOGRAPHY CHAPTER FIVE: FLOODS Name: _______________________________ ( ) Class: 2 _______________ Date: ______________ Definition of floods Floods are large amounts of water that overflows onto land that is usually dry. Types of floods (1) Coastal floods • Occur in areas along the coast (especially low-‐lying coastal land, such as river mouths). • Are caused by intense storms (eg. as tropical storms, typhoons or hurricanes) or tsunamis. • During storms, strong winds cause large waves known as storm surges. These storm surges bring about higher water levels that lead to coastal floods. (2) River floods • Occur when water in the river rises and overflows its banks. • Occur on the floodplain, which consists of the river and the low-‐lying land on either side of it. • May be caused by dam failure, snowmelt or heavy rainfalls. (3) Flash floods • Takes place suddenly and lasts for a short period of time. • It is recognised by its quick rise in water level. • May be caused by heavy rainfall, coastal floods or river floods. Causes of floods (A) Heavy rainfall • Characteristics of rainfall include: o Rainfall duration (hours) refers to how long the rain event lasts for. o Rainfall intensity (mm/h) refers to the rate at which rain falls to the ground. Tropical storms usually have a high rainfall intensity. o Rainfall frequency refers to the probability that a certain amount of rain falling within a certain period of time will occur (eg. England experienced a 1-‐in-‐50-‐year storm in June 2012). GQ1 What are floods?
- 2. • In densely built up areas, rainwater may not be able to infiltrate the ground or be drained off fast enough during a heavy rain or prolonged rainfall event. The accumulation of rainwater on the ground surface thus leads to flooding. (B) Snowmelt • When ice and snow on the ground or mountain melt, snowmelt flows over the land into rivers, increasing the amount of water in the river. This causes the river to overflow its banks and flood the surrounding areas. (C) Storm surge • During a storm, strong winds push water towards the coast. This creates huge waves which are piled up against the coastline, causing the areas near the coast to become flooded. (4) Failure of man-‐made structures • Examples of man-‐made structures: o Dams (a barrier built across a river) o Levees (raised banks that act as flood barriers) o Floodwalls (flood barriers that are made of concrete) • When these structures crack or collapse, large amounts of water previously stored behind these structures will gush through and flood the surrounding areas. Which cities are prone to floods? Floods can occur almost anywhere. Factors that cause cities to be more prone to floods (I) Height of land above sea level • Cities that are located on low-‐lying lands are more prone to floods because even a little rise in sea level will cause these cities to experience flooding. (II) Proximity to water bodies • Cities located near water bodies are more prone to floods because these cities would experience flooding whenever water overflow the banks of these water bodies. (III) Permeability of surface cover • Permeability refers to how easy water can infiltrate into the ground. • As concrete surfaces are almost impermeable, water cannot infiltrate the ground. This leads to a higher surface runoff and eventually a higher likelihood of floods. • As vegetated surfaces are more permeable, water can infiltrate the ground easily. This leads to less surface runoff, thereby lowering the likelihood of floods. GQ2 Why are some cities more prone to floods than others?
- 3. (IV) Channel capacity • Floods may occur when the amount of rain exceed the capacity of the channel. • In cities with a high proportion of built-‐up areas and concrete surfaces, it is likely to experience large amounts of surface runoff during a rain event. Canals may not have the capacity to carry this runoff away fast enough, thereby leading to floods. Flooding in cities tends to affect many people due to the high population densities in cities. Impact of floods (A) SOCIAL IMPACTS 1) Injuries and loss of lives • Fast moving floods waters can cause buildings to collapse. • Objects and debris are also washed along by fast-‐moving water. • As a result, people and livestock are swept away and it can cause injuries and deaths. 2) Affects physical health • As people may get caught in the flood for too long, it can cause people to suffer from hypothermia (symptoms of constant shivering, confusion & loss of coordination). 3) Affects emotional and mental health • Loss of homes or livestock due to floods can cause mental stress to people. • Loss of loved ones or family members during a flood can cause emotional distress to flood victims. 4) Spread of diseases • During a flood, water supplies may be contaminated by chemical spills. This cause people to be exposed to contaminated drinking water which results in the spread of cholera and dysentery. • Stagnant pools of floodwater encourage mosquitoes to breed and this leads to more cases of malaria and dengue fever. 5) Homelessness • Floodwaters can damage property and sweep houses away. This cause people to lose a roof over their head and people may have to evacuate to emergency shelters. 6) Disruption to clean water supply • Floodwaters can damage water pipes and this causes disruption to water supply. • Water supply may also be contaminated due to burst sewage pipes. GQ3 How do floods affect people living in cities?
- 4. Impact of floods (continued) (B) ECONOMIC IMPACTS 1) Damage to machinery and equipment • Machinery and equipment may be submerged or damaged by floodwaters. • As a result, factories are unable to operate and this causes them to suffer economic losses. • Companies may lose profits and have to spend money buying new equipment. 2) Damage to transport infrastructure • Transport infrastructure may be submerged or damaged by floodwaters. • As a result, people are unable to travel to work and tourists may not want to visit this area. • This causes an overall reduction in productivity, employment and profits. 3) Disruption to energy supply • During a flood, power lines may be damaged. This causes power outages to occur and leads to the lack of electricity. • As a result, companies and factories are unable to operate. This leads to the loss of employment and income for individuals and companies.