A flood is a natural disaster brought about by a combination of factors: Physical and climatic. A flood is the rising of a body of water and its overflowing onto normally dry land. Floods can be caused by heavy rains that pour too much water into rivers and other waterways. Making these natural channels unable to carry all the water. Rising water flows over or breaks the banks to the waterways causing the surrounding land to be flooded. In Australia floods mostly occur in coastal areas. Just because an area hasn’t had rain before we can not rule out that the area will never flood. Floods can occur almost anywhere. There are three main types of floods
1. Slow onset floods-usually occurs on inland rivers. This type floods take at least a week to develop and can persist for months. As heavy rain falls, the river is unable to take in the extra water. This causes the river to overflow its banks.
2. Rapid onset floods- Rapid onset floods usually occur in coastal rivers. These occur more quickly than slow onset floods and they can be more dangerous because there is less warning than with slow-onset floods. Since these rivers drain more quickly than slow-moving inland rivers, flooding happens more quickly, over the course of a couple of days.
3. Flash floods-occur when extremely heavy rain falls due to storms. Flash floods have been seen to be too much for local drainage systems to handle.
Geographical processes
Associated with floods
One geographical process associated with floods is thunderstorms. Thunderstorms are a form of weather characterized by the presence of lightning. It is usually accompanied by heavy rain and sometimes snow or hail.
Another geographical process is La Niña. The term La Niña refers to the cooling of the central and eastern Pacific Ocean. In Australia (particularly eastern Australia), La Niña events are associated with increased probability of wetter conditions (storms and or heavy rain) causing floods.
Changes to the atmosphere and ocean circulation during La Niña events include:
• Cooler than normal ocean temperatures across the central and eastern tropical Pacific Ocean.
• Increased cloudiness over tropical Australia.
• Stronger than normal (easterly) winds across the Pacific Ocean.
• High values of the SOI (Southern Oscillation Index).
Economic impact
Floods may also cause millions of dollars worth of damage to a city from evicting people from their homes; ruining businesses, ruining mining industries, infrastructure such as roads and bridges, farming properties. Floods cause significant amounts of erosion to coasts, leading to more frequent flooding if not repaired. There could be loss of money because of decline in tourism for the time the flood occurs.
Impact on the society
Floods make an enormous impact on the society. Floods destroy drainage systems in cities, causing raw sewage to spill out into bodies of water. Also, in cases of severe floods, buildings can be significantly damaged and even destroyed. Fresh water becomes scarce. Un hygienic conditions may spread water borne diseases throughout the flooded area. Also floods destroy peoples home there lively hood and there careers.
Environmental impact
Floods can have catastrophic effects on the environment as many toxic materials such as paint, pesticide and gasoline can be released into the rivers, lakes, bays, and the ocean, killing maritime life. Non tolerant tree species can also suffocate. However, floods do make a slight positive impact on the environment. Floods spread sediment containing beneficial nutrients to topsoil that might never arrive there otherwise.
Flood emergency responses
The NSW State Emergency Service (SES) is volunteers that help their communities cope with emergencies. More than 10,000 volunteers give up their time in 228 locations throughout NSW to assist their communities during floods, storms and other emergencies. In response to a flood the SES provide strategic guidance for effective emergency response to flood events. They also forecast the upcoming meteorological events, spread the information to the community to minimise the threat and impact to people, property and the environment. The government also create flood recovery centres for people who have lost homes and have nowhere else to go.
The big wet 1973-74
The big wet in 1973 was one of the wettest known over much of Australia; La Nina was one of the main effects that caused the floods. The 1973/74 northern wet season started early. By the end of 1973 large areas of the country were saturated. New Year celebrations had barely finished when torrential rains on 4th January soaked northeast Victoria and parts of the Riverina, and flooded Albury. Also in north Queensland, big floods on the 5th marooned cars and coaches across a broad area. Further heavy rain fell in NSW during the second week of January. Many rivers in the north of New South Wales were flooded. On 11 January, creeks in Brisbane burst their banks, flooding roads and streets. Northern Victoria experienced a second burst of heavy rain on the 13th this time, floodwaters swirled through the streets of Nhill and Dimboola. About 500 people were evacuated from Normanton and Karumba, while 250 stranded passengers on the Townsville-Mt Isa railway were air-lifted to Mt Isa. Around 400-600mm of rain saturated the southern Northern Territory and southwest Queensland in January, more than twice the average ANNUAL total at some locations. To make things worse tropical cyclone Wanda this moved ashore north of Brisbane on Thursday 24th January, producing little wind damage, but sending down enormous amounts of rain over the Australia Day weekend. In Brisbane, intensifying rain throughout Friday dumped over 300mm within 24 hours. In three days (ended 27th) the Queensland capital received 580mm, with even heavier falls over river catchments near the city (1,300mm in five days at Mt Glorious). Fourteen people were drowned, some trapped in offices by the rising waters. Vast areas of the inland remained submerged for weeks - in some cases, for months. Crops were destroyed, and outbreaks of disease, such as Murray Valley encephalitis, took many lives.
Bibliography
www.bom.gov.au target="_blank" class="qa" rel="external">en.wikipedia.org
1. Slow onset floods-usually occurs on inland rivers. This type floods take at least a week to develop and can persist for months. As heavy rain falls, the river is unable to take in the extra water. This causes the river to overflow its banks.
2. Rapid onset floods- Rapid onset floods usually occur in coastal rivers. These occur more quickly than slow onset floods and they can be more dangerous because there is less warning than with slow-onset floods. Since these rivers drain more quickly than slow-moving inland rivers, flooding happens more quickly, over the course of a couple of days.
3. Flash floods-occur when extremely heavy rain falls due to storms. Flash floods have been seen to be too much for local drainage systems to handle.
Geographical processes
Associated with floods
One geographical process associated with floods is thunderstorms. Thunderstorms are a form of weather characterized by the presence of lightning. It is usually accompanied by heavy rain and sometimes snow or hail.
Another geographical process is La Niña. The term La Niña refers to the cooling of the central and eastern Pacific Ocean. In Australia (particularly eastern Australia), La Niña events are associated with increased probability of wetter conditions (storms and or heavy rain) causing floods.
Changes to the atmosphere and ocean circulation during La Niña events include:
• Cooler than normal ocean temperatures across the central and eastern tropical Pacific Ocean.
• Increased cloudiness over tropical Australia.
• Stronger than normal (easterly) winds across the Pacific Ocean.
• High values of the SOI (Southern Oscillation Index).
Economic impact
Floods may also cause millions of dollars worth of damage to a city from evicting people from their homes; ruining businesses, ruining mining industries, infrastructure such as roads and bridges, farming properties. Floods cause significant amounts of erosion to coasts, leading to more frequent flooding if not repaired. There could be loss of money because of decline in tourism for the time the flood occurs.
Impact on the society
Floods make an enormous impact on the society. Floods destroy drainage systems in cities, causing raw sewage to spill out into bodies of water. Also, in cases of severe floods, buildings can be significantly damaged and even destroyed. Fresh water becomes scarce. Un hygienic conditions may spread water borne diseases throughout the flooded area. Also floods destroy peoples home there lively hood and there careers.
Environmental impact
Floods can have catastrophic effects on the environment as many toxic materials such as paint, pesticide and gasoline can be released into the rivers, lakes, bays, and the ocean, killing maritime life. Non tolerant tree species can also suffocate. However, floods do make a slight positive impact on the environment. Floods spread sediment containing beneficial nutrients to topsoil that might never arrive there otherwise.
Flood emergency responses
The NSW State Emergency Service (SES) is volunteers that help their communities cope with emergencies. More than 10,000 volunteers give up their time in 228 locations throughout NSW to assist their communities during floods, storms and other emergencies. In response to a flood the SES provide strategic guidance for effective emergency response to flood events. They also forecast the upcoming meteorological events, spread the information to the community to minimise the threat and impact to people, property and the environment. The government also create flood recovery centres for people who have lost homes and have nowhere else to go.
The big wet 1973-74
The big wet in 1973 was one of the wettest known over much of Australia; La Nina was one of the main effects that caused the floods. The 1973/74 northern wet season started early. By the end of 1973 large areas of the country were saturated. New Year celebrations had barely finished when torrential rains on 4th January soaked northeast Victoria and parts of the Riverina, and flooded Albury. Also in north Queensland, big floods on the 5th marooned cars and coaches across a broad area. Further heavy rain fell in NSW during the second week of January. Many rivers in the north of New South Wales were flooded. On 11 January, creeks in Brisbane burst their banks, flooding roads and streets. Northern Victoria experienced a second burst of heavy rain on the 13th this time, floodwaters swirled through the streets of Nhill and Dimboola. About 500 people were evacuated from Normanton and Karumba, while 250 stranded passengers on the Townsville-Mt Isa railway were air-lifted to Mt Isa. Around 400-600mm of rain saturated the southern Northern Territory and southwest Queensland in January, more than twice the average ANNUAL total at some locations. To make things worse tropical cyclone Wanda this moved ashore north of Brisbane on Thursday 24th January, producing little wind damage, but sending down enormous amounts of rain over the Australia Day weekend. In Brisbane, intensifying rain throughout Friday dumped over 300mm within 24 hours. In three days (ended 27th) the Queensland capital received 580mm, with even heavier falls over river catchments near the city (1,300mm in five days at Mt Glorious). Fourteen people were drowned, some trapped in offices by the rising waters. Vast areas of the inland remained submerged for weeks - in some cases, for months. Crops were destroyed, and outbreaks of disease, such as Murray Valley encephalitis, took many lives.
Bibliography
www.bom.gov.au target="_blank" class="qa" rel="external">en.wikipedia.org