Topic:

Floods

1. What are they?2. Natural causes of floods3. Human causes of floods

4. Consequences5. How to decrease the impact

By Olia Litvina 10-A group

Floods. What are they?

A flood is an overflow of water that submerges land which is usually dry. The European Union (EU) Floods Directive defines a flood as a covering by water of land not normally covered by water. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Flooding may occur as an overflow of water from water bodies, such as a river or lake, in which the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries, or it may occur due to an accumulation of rainwater on saturated ground in an areal flood. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, these changes in size are unlikely to be considered significant unless they flood property or drown domestic animals.Floods can also occur in rivers when the flow rate exceeds the capacity of the river channel, particularly at bends or meanders in the waterway. Floods often cause damage to homes and businesses if they are in the natural flood plains of rivers. While riverine flood damage can be eliminated by moving away from rivers and other bodies of water, people have traditionally lived and worked by rivers because the land is usually flat and fertile and because rivers provide easy travel and access to commerce and industry.Some floods develop slowly, while others such as flash floods, can develop in just a few minutes and without visible signs of rain. Additionally, floods can be local, impacting a neighbourhood or community, or very large, affecting entire river basins.Etymology. The word "flood" comes from the Old English flod, a word common to Germanic languages (compare German Flut, Dutch vloed from the same root as is seen in flow, float; also compare with Latin fluctus, flumen). Deluge myths are mythical stories of a great flood sent by a deity or deities to destroy civilization as an act of divine retribution, and they are featured in the mythology of many cultures.

Natural causes of floods

1.High rainfall

Heavy rainfall raises the water level. When the water level is higher than the river bank or the dams, the water comes out from the river,there will be flooding.

2.Snowmelt

Because of global warming, the temperature of this year is higher than the temperature of many years ago.The ice caps melt in spring, and the water goes into the sea. The water raises the sea level, and makes the river level rise. When river level rises, flooding may occur. external image 130109-west-bank-flooding-747a.photoblog600.jpg

3.Relief

Flooding often occurs in lowlands. This is because rivers flow more slowly in low-lying areas. If the water volume increases suddenly, floods occur.

4.Coastal flooding

Flooding always occurs in coastal areas. High tides or storms cause the water level to rise. If the water level is higher than the level of the coastal lowland, flooding will occur.

Human causes of floods1.Deforestation

Large areas of forests near the rivers have been cleared. The lands are used to make room for settlement, roads and farmland. Less vegetation protects the soil, the soil is quickly lost to rivers and the sea.This raises the river bed, so the river overflows its banks easily.

2.Poor farming

Some farming practices can damage the vegetation cover, so the soil will be washed into the river easily.

Overgrazing People want more food and money. They graze too many animals on the land and the pasture is eaten away quickly. Less vegetation cover

results in soil washed into the rivers easily. external image iowa7.jpg

Overcultivation When a piece of land has been used for farming for a long period of time, the soil may became so infertile that no vegetation can grow on

it. The land is less fertile than before so the soil washed into the rivers more easily

3.Poor water management

When the dams are poorly constructed or maintained ,they can easily collapse and this results in flooding. In China, many lakes along the major rivers have been heavily silted and reclaimed,.

4.Population pressure

Because of large amounts of people, everything needs more, like wood, land and food…… Soil erosion happens more often and increases the risk of flooding.

Large numbers of people live in areas with high risk of flooding in China. They cause the problems of overgrazing and overcultivation.Flooding can have many different effects on the environment and on societies that are situated near flood risk areas. Floods can destroy drainage and sewer systems in cities causing sewage to contaminate other bodies of water which in turn can lead to the spread of water

borne diseases.

Consequences

With toxic materials being released into rivers, lakes and reservoirs the impact on both the natural environment and human civilisation can be enormous. Marine life can be killed in large numbers due to this pollution, while clean drinking water for humans can become scarce as a result. Crops can be affected, destroying foodstuffs and leading to starvation if the wrong areas are hit.

Floods can also cause erosion which can have all sorts of effects depending on the situation. One of the most serious of these is a possible landslide. Property, houses and other buildings can all be destroyed while cars can find attempting to drive in flooded conditions treacherous.

Of course, there is a certain amount of natural flooding which occurs in rivers, and it should be realised that the lakes and watercourses we see today are all the result of flooding in one form or another over history. It is a good example of the Buddhist doctrine of impermanence and it is only really the human point of view which looks at flooding and sees it as a natural disaster because really it is just water moving from one place to another, it just may be inconvenient for us. We should remember that floods can spread sediment containing beneficial nutrients to topsoil that would otherwise not receive it.

Because of the floods the water is pushing away all of the trees. All of the rocks are disintegrating of the waters current. The flooding has blocked up the draining making the sewers overload, which is howwater born diseases, start to spread. Also the flooding it has destroyed the crops making it hard to find food, for all the people. Because of the flooding is making the building collapse away, the toxic paint, pesticide and gasoline can be released to the water harming the environment.

Floods destroy homes, kill animals and humans alike but they also bring fresh soil and new life to the land they effect.

How to reduce the impact of floods

Methods of controlTemporary Perimeter BarriersIn 1988, a method of using water to control was discovered. This was accomplished by containing 2 parallel tubes within a third outer tube. When filled, this structure formed a non-rolling wall of water that can control 75% of its height in external water depth, with dry ground behind it. 8' tall water filled barriers were used to surround Fort Calhoun Nuclear Generating Station during the 2011 Missouri River Flooding. Instead of trucking in sandbag material for a flood, stacking it, then trucking it out to a hazmat disposal site, flood control can be accomplished by using the on site water.DamsMany dams and their associated reservoirs are designed completely or partially to aid in flood protection and control. Many large dams have flood-control reservations in which the level of a reservoir must be kept below a certain elevation before the onset of the rainy/summer melt season so as to allow a certain amount of space in which floodwaters can fill. The term dry dam refers to a dam that serves purely for flood control without any conservation storage (e.g. Mount Morris Dam, Seven Oaks Dam).Self-closing flood barrierThe self-closing flood barrier (SCFB) is a flood defense system to protect people and property from inland waterway floods caused by heavy rainfall, gales or rapid melting snow. The SCFB can be built to protect residential properties and whole communities, as well as industrial or other strategic areas. The barrier system is constantly ready to deploy in a flood situation, it can be installed in any length and uses the rising flood water to deploy. Barrier systems have already been built and installed in Belgium, Italy, Ireland, the Netherlands, Thailand, United Kingdom, Vietnam, Australia, Russia and the United States. Millions of documents at the National Archives building in Washington DC are protected by two SCFBs.River defencesIn many countries, rivers are prone to floods and are often carefully managed. Defences such as levees, bunds, reservoirs, and weirs are used to prevent rivers from bursting their banks. When these defences fail, emergency measures such as sandbags or portable inflatable tubes are used.A weir, also known as a lowhead dam, is most often used to create millponds, but on the Humber River in Toronto, a weir was built near Raymore Drive to prevent a recurrence of the flood damage caused by Hurricane Hazel in 1954.Coastal defencesCoastal flooding has been addressed in Europe and the Americas with coastal defences, such as sea walls, beach nourishment, and barrier islands.Tide gates are used in conjunction with dykes and culverts. They can be placed at the mouth of streams or small rivers, where an estuary begins or where tributary streams, or drainage ditches connect to sloughs. Tide gates close during incoming tides to prevent tidal waters from moving upland, and open during outgoing tides to allow waters to drain out via the culvert and into the estuary side of the dike. The opening and closing of the gates is driven by a difference in water level on either side of the gate.

The End

Thank you for your attention.Take care of yourself and nature!