What are floods and what causes them

A flood occurs when water overflows or inundates land that’s normally dry. This can happen in a multitude of ways. The most common are when rivers or streams overflow their banks. Excessive rain, a ruptured dam or levee, rapid ice melting in the mountains, or even a beaver dam can overwhelm a river and send it spreading over the adjacent land, called a floodplain. Coastal flooding occurs when a large storm or tsunami causes the sea to surge inland.

Most floods take hours or even days to develop, giving residents ample time to prepare or evacuate. Others generate quickly and with little warning. These flash floods can be extremely dangerous, instantly turning a babbling brook into a thundering wall of water and sweeping everything in its path downstream.

Disaster experts classify floods according to their likelihood of occurring in a given time period. A hundred-year flood, for example, is an extremely large, destructive event that would theoretically be expected to happen only once every century. But this is a theoretical number. In reality, this classification means there is a one-percent chance that such a flood could happen in any given year. Over recent decades, possibly due to global climate change, hundred-year floods have been occurring worldwide with frightening regularity.

Moving water has awesome destructive power. When a river overflows its banks or the sea drives inland, structures poorly equipped to withstand the water’s strength are no match. Bridges, houses, trees, and cars can be picked up and carried off. The erosive force of moving water can drag dirt from under a building’s foundation, causing it to crack and tumble.

Most floods take hours or even days to develop, giving residents ample time to prepare or evacuate. Others generate quickly and with little warning. These flash floods can be extremely dangerous, instantly turning a babbling brook into a thundering wall of water and sweeping everything in its path downstream.

Disaster experts classify floods according to their likelihood of occurring in a given time period. A hundred-year flood, for example, is an extremely large, destructive event that would theoretically be expected to happen only once every century. But this is a theoretical number. In reality, this classification means there is a one-percent chance that such a flood could happen in any given year. Over recent decades, possibly due to global climate change, hundred-year floods have been occurring worldwide with frightening regularity.

Moving water has awesome destructive power. When a river overflows its banks or the sea drives inland, structures poorly equipped to withstand the water’s strength are no match. Bridges, houses, trees, and cars can be picked up and carried off. The erosive force of moving water can drag dirt from under a building’s foundation, causing it to crack and tumble.

When floodwaters recede, affected areas are often blanketed in silt and mud. The water and landscape can be contaminated with hazardous materials, such as sharp debris, pesticides, fuel, and untreated sewage. Potentially dangerous mold blooms can quickly overwhelm water-soaked structures. Residents of flooded areas can be left without power and clean drinking water, leading to outbreaks of deadly waterborne diseases like typhoid, hepatitis A, and cholera.

But flooding, particularly in river floodplains, is as natural as rain and has been occurring for millions of years. Famously fertile floodplains like the Mississippi Valley in the American Midwest, the Nile River valley in Egypt, and the Tigris-Euphrates in the Middle East have supported agriculture for millennia because annual flooding has left millions of tons of nutrient-rich silt deposits behind.

Most flood destruction is attributable to humans’ desire to live near picturesque coastlines and in river valleys. Aggravating the problem is a tendency for developers to backfill and build on wetlands that would otherwise act as natural flood buffers.

Many governments mandate that residents of flood-prone areas purchase flood insurance and build flood-resistant structures. Massive efforts to mitigate and redirect inevitable floods have resulted in some of the most ambitious engineering efforts ever seen, including New Orleans’s extensive levee system and massive dikes and dams in the Netherlands. And highly advanced computer modeling now lets disaster authorities predict with amazing accuracy where floods will occur and how severe they’re likely to be.

In the United States, where flood mitigation and prediction is advanced, floods do about $6 billion worth of damage and kill about 140 people every year. A 2007 report by the Organization for Economic Cooperation and Development found that coastal flooding alone does some $3 trillion in damage worldwide. In China’s Yellow River valley, where some of the world’s worst floods have occurred, millions of people have perished in floods during the last century.

Top 10 Deadliest Floods in History

10. North Sea Flood (1212)

The Netherlands has a long history of series of floods. One of the most obvious reason is that the country is originally formed by three large estuaries of the Rhine, the Meuse and the Scheldt river and their other tributaries. The 1212 North sea flood may not be the worst floods ever occurred in the country, but it killed around 60,000 people. Whenever a flood of this magnitude occurs, no matter how advanced you are, you fell just helpless. It took years to rebuild the flood affected region.

9. St. Lucia Flood (1287)

St. Lucia Flood affected Netherlands and North Germany on 12th December 1287. This is the sixth largest flood in the history of the nation, which took the lives of nearly 80,000 people. The main reason of this catastrophe was a combination of a high spring tide and a severe European windstorm and low pressure which led to a rise in water level more than 5.6 meters (18.4 ft) above mean sea level in the north sea. The 1287, St. Lucia flood had a major influence on the subsequent history of the Netherlands.

8. Yangtze River Flood (1911)

The 1911, Yangtze River Flood is one of the deadliest disasters that China has ever experienced. Chang Jiang or the Yangzi, pronounced as Yangtze, is the longest river in Asia and the third longest in the world.  It flows for 6300 km from the Qinghai glaciers in Tibet to the East China sea at Shanghai. This river is the main source of irrigation, transport in China. The largest hydroelectric power station in the world was built on this river. In 1911, it killed around 1,00,000 people and cause severe property loss.

7. Red River and Hanoi Delta Flood (1971)

The Red River Delta is stretched over some 15,000 square km, in northern Vietnam. In 1971, during the Vietnam war, the Red River delta flood killed more than 1,00,000 people in Hanoi.

6. St. Felix Flood (1530)

The St. Felix Flood happened on 5th November 1530, on the name day of ST. Felix, in the Netherlands. Most of the land of the Netherlands was washed away and more than 1,20,000 people were killed. Nowadays, the submerged area, including large parts of Flanders, Zeeland and Reimerswaal cities have completely turned into the salt marsh area. The day was later recognized as Evil Saturday (or Kwade Zaterdag) in the Dutch history.

5. Yangtze River Flood (1935)

In 1935, another flood had hit the southeastern China, on the Yangtze River. The Yangtze valley, is amongst the most frequently flooded areas in the world, that naturally floods every summer. This one was even more cruel than the 1911 floods. It killed more than 1,50,000 people and destroyed everything that the residents of the valley had ever possessed. Due to the flood, dangerous water-borne diseases, Malaria, Dermatitis and Tuberculosis, plagued the entire nation.

4. Banqiao Dam Failure (1975)

The Banqiao Reservoir Dam is situated on the River Ru in Henan province, China. In 1975, Banqiao Reservoir was among the 62 dams in Zhumadian city that were destroyed during Typhoon Nina. According to People’s Daily, the dam was designed to survive over 300mm of rainfall per day, but the Typhoon caused the rainfall almost twice as much that the dam can handle. In August 1975, the breakdown of this dam lead to the China half flooded. More than 1,60,000 people were killed and millions of people were stuck under water for days fighting for their survival. According to the reports, approximate property loss was over $500 million.

3. Yellow River Flood (1938)

The Yellow river flood of 1938, was the largest act of environmental warfare. During the second Sino-Japanese war, China was under pressure from Japanese forces. The then Nationalist Government decided to halt the forces from further advancement. As a plan, they decided to destroy the dikes at the Yellow river, letting the river freely flow into the settlements near Henan, Anhui and Jiangsu province. There was nothing to gain; the strategic value of the flood has been questioned. Japanese troops were out of its range; moreover, they were not able to stop their forces. Reports indicate that around 8,00,000 people drowned.

2. Yellow River Flood (1887)

51 years before the 1938 Yellow river flood, there was another catastrophe happened in 1887 in the same Yellow River in China. On 28th September 1887 the river’s water overflow and killed more than 9,00,000 people. More than 2 million people were homeless and over 50,000 square km of land got submerged, destroyed agricultural lands and commercial centers.

1. China Flood (1931)

Considered the deadliest flood in the history of humankind. During 1930, a severe drought afflicted almost the entire country of China. Heavy snowstorms in the winter of 1930 followed by heavy rains raised river levels significantly. In 1931, the conditions become much worse as the country experienced extreme cyclone activity. The final destruction started in July 1931, when the water level in the three biggest rivers exceeded maximum limits. Official Chinese sources claimed that nearly 145,000 lost their lives. Most external sources claimed that it was much higher, as much as 4 to 5 million people.