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What is a flood in hydrology?
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Flooding is an overflowing of water onto land that is normally dry. Floods can happen during heavy rains, when ocean waves come on shore, when snow melts quickly, or when dams or levees break. Damaging flooding may happen with only a few inches of water, or it may cover a house to the rooftop.
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noun. (Netherlands) series of dams and drainage systems designed to isolate and dam the Zuiderzee, an inlet of the North Sea. A flood happens when water overflows or soaks land that is normally dry. There are few places on Earth where people don’t need to be concerned about flooding.
- Overview
- How floods form
- Dramatic pictures reveal Venice flooding
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Floods are among Earth's most common–and most destructive–natural hazards.
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A flood occurs when water inundates land that's normally dry, which can happen in a multitude of ways.
Excessive rain, a ruptured dam or levee, rapid melting of snow or ice, or even an unfortunately placed beaver dam can overwhelm a river, 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 time to prepare or evacuate. Others generate quickly and with little warning. So-called flash floods can be extremely dangerous, instantly turning a babbling brook or even a dry wash into rushing rapids that sweep everything in their path downstream.
Climate change is increasing the risk of floods worldwide, particularly in coastal and low-lying areas, because of its role in extreme weather events and rising seas. The increase in temperatures that accompanies global warming can contribute to hurricanes that move more slowly and drop more rain, funneling moisture into atmospheric rivers like the ones that led to heavy rains and flooding in California in early 2019.
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People walk on a catwalk in a flooded St. Mark's Square during a period of seasonal high water in Venice, Italy, on October 29, 2018.
People walk on a catwalk in a flooded St. Mark's Square during a period of seasonal high water in Venice, Italy, on October 29, 2018.
Floods cause more than $40 billion in damage worldwide annually, according to the Organization for Economic Cooperation and Development. In the U.S., losses average close to $8 billion a year. Death tolls have increased in recent decades to more than 100 people a year. In China's Yellow River Valley some of the world's worst floods have killed millions of people.
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.
Flooding, particularly in river floodplains, is as natural as rain and has been occurring for millions of years. Famously fertile floodplains such as the Mississippi Valley, the Nile River Valley in Egypt, and the Tigris-Euphrates in the Middle East have supported agriculture for millennia because annual flooding has left tons of nutrient-rich silt deposits behind. Humans have increased the risk of death and damage by increasingly building homes, businesses, and infrastructure in vulnerable floodplains.
To try to mitigate the risk, many governments mandate that residents of flood-prone areas purchase flood insurance and set construction requirements aimed at making buildings more flood resistant—with varying degrees of success.
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. Such efforts continue today as climate change continues to put pressure on vulnerable areas. Some flood-prone cities in the U.S. are even going beyond federal estimates and setting higher local standards for protection.
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- Christina Nunez
Sep 15, 2023 · But what is a flood, exactly? In this article, we'll discover what makes water change character so rapidly and see what happens when it does. Contents. Water, Water Everywhere. Under the Weather. Take Me to the River. Spread of Disease. Water, Water Everywhere. Flooding of farmland in Missouri.
A flood is an overflow of water that submerges land that is usually dry. Floods are an area of study in the discipline of hydrology. They are the most common and widespread natural severe weather event. Floods can look very different because flooding covers anything from a few inches of water to several feet.
1 day ago · Flood, high-water stage in which water overflows its natural or artificial banks onto normally dry land, such as a river inundating its floodplain. The effects of floods on human well-being range from unqualified blessings to catastrophes. The regular seasonal spring floods of the Nile River prior.
A flood is an overflow of water (or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant concern in agriculture, civil engineering and public health.
