Flood

Examples of major floods

Flooding occurs all over the world. The examples of major floods mentioned below illustrate this.

- In November 2006, major floods hit large parts of Somalia, killing at least 52 people and displacing 50,000 others. The government appealed for international help to prevent a humanitarian catastrophe
- In November 2006, heavy rain caused large parts of Afghanistan to flood. The official death toll was set on 80, and it took more than two days to reach some of the most severely flooded villages
- In August 2006, a major part of Ethiopia was flooded
- Widespread flood of the Mid-Atlantic region of the eastern United States in 2006. At least 16 deaths. Delaware, Columbia, New Jersey, Maryland, Pennsylvania, Virginia, and New York are stricken.
- In May 2006, a major part of Korea was flooded
- In April 2006, the Danube River flooded large parts of Budapest, Hungary. Margit Island was completely under water for a significant amount of time
- In November 2005, some Indian states in the Bay of Bengal were isolated due to heavy rainfall
- In August 2005, major parts of Eastern Europe were flooded due to heavy rainfall
- In August 2005, hurricane Katrina hit New Orleans, the hurricane destroyed levees and floodwalls in the river area, causing 80% of the town to be flooded. Some parts were more than six metres under water. More than 80% of the residents were evacuated, and many were housed in the Louisiana Superdome last-minute. The official death toll from the flood was set on 1,577. Economic and political damage lasted well into 2006
- In July 2005, parts of Mumbai India were severely flooded. In some areas the water was more than 4.5 metres high. The flood cost over 700 lives
- In June 2005, Alberta, Canada was flooded, lasting three weeks and demanding 72 lives
- In 2000 large parts of Mozambique were flooded after a cyclone, killing thousands of people
- In the summer of 1998, China experienced major floods of the Yangtze River, killing more than 3,000 people, and leaving 14 million homeless
- In 1994 and 1995 heavy rainfall caused Rivers to flood parts of The Netherlands (see picture). Many people in the province of Limburg were evacuated, and dikes in other provinces threatened to break through
- In 1993 the Great Flood hit the American Midwest. The official death toll was 28, and 10,000 homes were destroyed along with 15 million acres of farmland
- In January 1992 large parts of South America flooded
- In 1965 hurricane Betsy flooded major parts of New Orleans, killing 40 people
- In 1957 about 400 people were killed in Louisiana by flooding caused by hurricane Audrey
- In 1955 the Australian Hunter Valley was flooded due to heavy rainfall. In total 25 people were killed, 2,000 cattle drowned, and millions of dollars of crop were destroyed
- In 1953 many Dutch and British citizens were killed in the North Sea flood. For an extensive description, see environmental disasters
- In 1952 a flood of Lynmouth, England, killed 34 people and destroyed over 80 buildings
- In 1951 heavy rains caused a flood in the Kansas River area, which cost 28 lives. Large parts of Kansas flooded, and damages amounted up to almost one billion dollars
- In 1937 the Ohio River flooded, damaging Pittsburgh and Cairo, Illinois. Approximately 385 people died and about one million were left homeless
- In 1931 major parts of China flooded, causing between 800,000 and 4,000,000 casualties
- In 1927 the United States experienced the Great Mississippi flood, as a result of heavy rainfall. The flood affected at least 7 different states, killing 246 people and displacing more than 700,000

Besides the floods mentioned above, marked as historical events, there were many more. Some floods are purely mythological. Myths of many different peoples tell of the Great Flood caused by the gods to create a new human race out of a single family. For an overview, check out our water mythology page.

Flood protection: innovations

The Thames Flood Barrier

London is a city quite susceptible to flooding. This is caused by the continual rise in the water level of the River Thames throughout the years, slow tilting of Britain because ice sheets from the ice age slowly lift land in the North, and the settlement of London on clay beds. Starting in 1974, a flood barrier over the River Thames was built by Woolwich reach. The structure was completed in 1982, and it was officially opened in 1984. After the Oosterscheldekering in The Netherlands, this is now the largest flood barrier in the world. It closes off part of the River Thames from the sea, and when opened ships can pass through it.

The direct cause of flood barrier construction was the flood of 1953, caused by a severe northwester storm. This flood killed a total of 307 people in the United Kingdom. But the Thames flooded before. It was reported that in 1236, a flood caused the halls of Westminster Palace to be under water. In 1663, Whitehall was flooded and many people drowned. The last time central London flooded was in 1928 when 14 people were killed. The death toll was much higher in 1953, because the flood reached London’s most populated low areas.

The Thames Flood Barrier has a total width of 520 metres. It consists of concrete piers, with ten separate rotating steel floodgates positioned across the river. Each floodgate can carry an overall load of more than 9,000 tonnes. By the riverbanks four additional radial gates are present, which can be lowered. The assignment for building the flood barrier was given by the Greater London Council (GLC). Rendel, Palmer and Tritton designed the barrier, and Charles Draper designed the floodgates. The Environmental Agency operates the barrier. When it no longer gives the protection needed because of rising water levels, the barrier is raised, and river walls are strengthened.

Some additional tidal defences were built to secure the flood barrier protective capacity. Downstream, 32 kilometres of flood defence called the Barking Barrier was constructed. It is a drop gate that allows for shipping passage when opened. Additionally, the downstream riverbanks were raised 2 metres. Upstream, defences of Putney and Hammersmith were raised to the level of the central London flood protection. In Putney, 80 kilometres of riverbanks were raised in 1971.

A total of 80 staff operate the barrier, lead by the Barrier Controller. The Storm Tide Forecasting Service (STFC) of the Meteorological Office must give warnings of dangerous conditions at least 36 hours in advance. The flood barrier is closed at least three to four hours before the peak of surge tide reaches the gates. Ships are warned by illuminating navigation signs on the banks.

The Dutch Afsluitdijk

In the northern portion of The Netherlands, the IJsselmeer can be found. This large water was called the Zuiderzee in the old days. In the 17th century Hendrik Stevin suggested closing of the Zuiderzee to prevent further breaching of dikes, leading to brackish water entering agricultural land. He suggested pumping the water out of the polders by steam engines, but this idea was not feasible at the time.

In the 1880s, the discussion on the Zuiderzee started up again, and the Zuiderzee Association was founded. Cornelis Lely became the advisor, and the minister of Transport and Public Works. He completed plans for the Zuiderzee, but these were not carried out than because of high costs. In 1913 the queen ordered for the works to be completed, but this was postponed until after World War I.

The Zuiderzee flood of 1916 made it evident that managing the Zuiderzee was a priority. Finally, the initial plan of Cornelis Lely was approved in 1918. In 1920, construction of a dike from North-Holland to Friesland started. It was named the Afsluitdijk, and was completed in 1932 (see picture). Drain locks are present in the dike to pump excess water from the (than renamed) IJsselmeer into the Waddenzee. It is 32 kilometres long, 90 metres wide and 7-7.5 metres over NAP high. It largely consists of boulder clay, a newly discovered material from Scandinavia. During construction parts of the IJsselmeer were drained, and new polders were created. By 1930 the area was completely impoldered.

The Delta Works

In the past 2000 years, The Netherlands has known many flood disasters. The main cause is the low position of the country compared to sea levels. The country owes its name to the fact that more than two-thirds of it lies below sea level. As early as 838, a large area of the north-western Netherlands was flooded by a storm tide. Consequences were severe, because no proper dikes were constructed back than. Large parts of the Dutch coastal area flooded, killing people and animals and destroying many houses. Sources state there may have been as many as 2,500 victims. In 1014 another flood occurred, breaching the coastline and flooding some of the southern islands. Thousands of people died, but an exact number is not known. In the 1400s two floods known as the Saint Elizabeth floods occurred. The first Elizabethan flood led to dike construction and polder creation. A large number of small towns were completely flooded. The second Elizabethan flood was caused by a north-western storm, and water flooding the west passed even the city of Dordrecht. A total of thirty towns were lost, and more than 2,000 people were killed. In 1570 the All Saints flood, the worst flood in The Netherlands so far, occurred. Many dikes collapsed, extremely large sections of coastline were flooded, and eventually almost 5/6 of the entire country was under water. Tens of thousands of people lost their homes, and more than 3,000 people died. Other floods in The Netherlands include the Saint Felix flood in 1530, the Christmas flood in 1717, and the Zuiderzee flood in 1916.

In 1953, a severe flood again hit the country (see picture). Causes and consequences are described on the environmental disasters page. After the flood, Minister Drees announced that restoring the dikes had the highest priority. Many volunteers worked on closing the holes created by the storm and the flood. Unit caissons were applied; large concrete blocks of many different variations. A Delta committee was appointed in August 1953. They first ordered for the movable storm surge barrier in the IJssel to be repaired. In 1958, the Delta Law was established based on flood repair and damage control experiences. The Delta plan, which was formed even before the flood of 1953, could now officially be carried out.

The Dutch government decided to build structures that would prevent major flood disasters from happening again, called the Delta Works. It started with building compartment dams, which divided the waterways into different compartments. This caused many of the waters to alter to freshwater lakes. Over the Haringvliet seventeen 60 metres wide sluices were built in 1971, and the Brouwersdam was finished a year later. A dam was also planned for the Oosterschelde, but people protested because they suspected the fishing industry would suffer from increasing saltiness the river water. In 1976 the Dutch government altered the plan to a storm surge barrier with a number of sluices. In 1986 the queen officially opened the barrier, containing 62 openings of 40 metres wide. It was called the Oosterscheldekering (see picture) and is one of the most famous water works in the world. In the 1990s, a movable barrier called the Maeslant Barrier was added to the structures, near Maassluis.

In total, the Delta works consisted of over 15,000 kilometres of flood bank, and over 300 dikes, barriers, sluices, floodgates, and other structures. The structures have many benefits, particularly to agriculture. Better control of the freshwater-saltwater border allows for freshwater application for irrigation water more readily. Additionally, streams in the area can be manipulated more easily, allowing freshwater in and letting polluted water out. The dams increase mobility between the islands, because it allowed for the construction of new roads. Nature and recreational developments are influenced by the presence of the structures.

Currently a lot of debate is going on about the Delta Works, because in the future sea level rise would demand the structures to be built higher and higher. The loss of habitable and arable land in the future due to flooding would cause major problems for Dutch economy. Many engineers are constantly trying to find solutions to expected consequences of climate change, particularly flooding. The trade centre of The Netherlands (the Randstad) is currently located in the west below sea level, and some people argue that relocating it to a more central plane would be best.

Flood protection: some general measures

Floodplains

Some countries, particularly the US, apply floodplains as a means of flood protection. The principle is relatively simple: parts of land around lakes, rivers or other water bodies are left uncultivated, for as far as the flood approximately ranges. This way, houses in the adjacent land are protected from flooding because it only occurs on the floodplain.

Wetlands are a commonly known land type applied as floodplains. They function as natural sponges that trap and slowly release floodwater (and rainwater). Trees and other vegetation also prevent the water from reaching the adjacent villages. Maintaining wetlands and other types of floodplains may prevent the requirement for costly flood protection measures such as dams and levees. Additionally, it minimizes intervention in land and waterways by engineering.

Sandbagging

In some cases floods are on their way or have already occurred, and the water force in combination with the weather may have damaged or may threaten to damage dikes. In this case, dikes can be sandbagged. Sandbags prevent water from flowing through, by the same principle as the actual dike that is re-enforced.

The bags are filled and properly placed to give the best protection. Any type of material (silt, clay, sand) can be applied, but sand is relatively easy to come by. To sandbag 30 metres of dike, approximately 3,400 bags are required for a dike of 1 metre height. The weight of the bags is generally limited to 15 kilos, so that the average adult can lift them. The army often carries out sandbagging, but local civilians may help depending on the urgency of the matter. The bags are filled halfway and are not tied.

Integrated flood management

The World Meteorological Organization (WMO) and the Global Water Partnership together have organized the Associated Programme on Flood Management. The overall goal of Integrated Flood Management (IFM) is maximizing net benefits from flood protection measures (see above), while minimizing the loss of life from flooding.

The integrated part of the management programme mainly concerns linking socio-economic development to natural ecosystem protection, and management of both land and water uses. The interaction between water bodies and land are viewed from both a flood protection, and a natural habitat point of view and hence the best possible flood protection tools are selected. Additionally, the local point of view is abandoned, and a more regional approach to land and flood management is followed.

Floods may have both positive and negative aspects. When heavy rains cause villages to be affected, this is generally viewed as negative. However, when floods occur on uncultivated land and leave fertile agricultural land, this is a positive effect. In Egypt, this generally occurs on the plains surrounding the river Nile, and farmers applied this as a means to gain cultivate new land for many centuries. IFM also integrates positive and negative effects of flood, to determine the proper course of action in a region.
 

Sources

Diodorus Siculus, 1939, Library of history – volume III, Loeb Classical Library, Harvard University Press, Cambridge, UK

http://www.waterhistory.org
http://www.wikipedia.org
http://www.iht.com/articles/ap/2006/11/20/asia/AS_GEN_Afghan_Flooding.php
http://www.mg.co.za/articlePage.aspx?articleid=290385&area=/breaking_news/breaking_news__africa/
http://www.environment-agency.gov.uk
http://www.deltawerken.com
http://www.epa.gov/owow/wetlands/flood.html
http://www.ag.ndsu.edu/pubs/ageng/safety/ae626w.htm