The flash flood is the most common cause of weather-related death in the United States. Water can rise several inches in a few hours.
A flood is an overflow of a body of water that submerges land not normally covered by water. While bodies of water rise with the tides and seasonal rains or snow melts, this is only considered flooding if the water engulfs areas where people live, causing damage or injury.
There are several types of floods. Riverine floods come in two kinds – fast and slow.
Slow floods are caused by sustained rainfall or snow melt, which creates a steady rise in the level of water. A slow flood can also occur when flow is blocked upstream by ice, mud, or debris. Fast ones include flash floods caused by intense thunderstorms and sudden releases from a dam or glacier.
The flash flood is the most common cause of weather-related death in the United States. Water can rise several inches in a few hours; in the case of arroyos or dry washes, a flood can develop in less than a minute. Most fatalities occur in vehicles, which can be swept away in only two feet of water.
- An estuarine flood occurs when sea tides cover beaches and coastal areas.
- A coastal flood is caused by severe sea storms or as an effect of a tsunami or earthquake. Both estuarine and coastal floods can be the result of a sea surge from a cyclone.
- A catastrophic or outburst flood is caused by a major event such as dam breakage, earthquake, or volcano eruption.
- Another type of flood is human-induced and includes accidental rupture of water mains or sewer pipes.
- A muddy flood occurs when too much runoff from cropland covers inhabited areas.
- Other types of flood are caused by an accumulation of water where it cannot evaporate, percolate into the soil, or run off; by a series of storms in one area; or by beavers damming a river or stream.
Flooding has both negative and positive effects. The negative effects can be sorted into immediate, secondary, and long-term damage.
- Immediate effects include injury and loss of life or property caused by the flood itself.
- Secondary effects involve dangers to residents and emergency aid workers from biological hazards (sewer pipes and dead animals release dangerous bacteria into the water), submerged hazards such as broken glass or jagged metal, and floating hazards such as automobiles. Clean water sources are contaminated, and food may also become scarce if crops are ruined. There are likely to be widespread power outages. Also, roads and bridges become impassable, leading to further food and supply shortages and making it difficult for emergency aid to reach those in need.
- Long-term effects are economic and social losses to a community. These can be caused by price increases due to food shortages, rebuilding costs, and a loss of income from tourism. Trees that are not flood-tolerant will die, which leads to erosion and future flood problems.
The positive effects, especially of smaller, seasonal flooding, more than balance out the negative. A number of myths worldwide tell of a flood that destroyed a civilization, only to abate and provide a chance for new life. Many rich agricultural areas, such as the Indus and Nile valleys, would not exist without a regular flood. Flooding enriches soil with nutrients and sediment and recharges the groundwater. It brings water to arid ecosystems. Flooding maintains biodiversity in floodplains and river corridors. It brings critical nutrients to lakes and rivers, which revitalizes the fish population and in turn feeds the birds. Hydroelectric power from regular flooding supports many communities in South Asia.
Flood-prone regions have devised ways to control the waters, such as dikes, canals, levees, and diversion. The Thames River in London has a mechanical barrier that can be raised to prevent high sea water from entering. After the Great Flood of 1910 in Paris, the government built reservoirs to take excess water from the Seine during its yearly flooding. Currently, the most elaborate flood control is found in the Netherlands to redirect water from the North Sea.
In North America, the Red River Floodway in Manitoba diverts floodwaters away from Winnipeg and other communities. In 2005, Hurricane Katrina proved the inadequacy of New Orleans’s complex system of levees and floodgates designed to protect the city, 35 percent of which is below sea level.
Floods are a natural part of the cycle of precipitation and growth. However, increasing population density and rising sea levels threaten to make them more dangerous and call for ever more sophisticated engineering solutions.
A flood is just one of many natural disasters that we should be aware of and prepare for. Other natural disasters include tornado, earthquake, wildfire, volcano, hurricane, avalanche, lightning and tsunami.
