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Date: 2022
Publisher: Gale, part of Cengage Group
Document Type: Topic overview
Length: 828 words
Content Level: (Level 3)
Lexile Measure: 1100L

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A flood is a natural disaster caused by an unexpected overabundance of water. Floods may occur naturally or may be caused by humans. Large amounts of water are often very destructive to human-made structures and inland ecosystems. However, floodwaters may also deposit large amounts of nutrients in soil, drastically increasing the soil’s fertility.

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Critical Thinking Questions

  • How are floods similar to other natural disasters? How are they different?
  • Why might climate change impact the frequency and severity of floods?
  • Have you ever experienced a flood? If so, describe your experience. If not, describe what you think it would be like to experience a flood.

Causes of Floods

Floods are caused by a variety of factors. Some are caused by unusually heavy rains, which overwhelm natural draining systems such as rivers, streams, and reservoirs. These natural sources overflow their banks, spilling large amounts of excess water into their environments. Strong waves and powerful winds, such as those found in hurricanes, can also naturally cause flooding. Some floods are caused in spring when ice and snow melt.

Floods may also be caused by human intervention. The placement or removal of dams usually floods large areas. Sometimes, people place dams to purposefully flood an area, causing a human-made lake. This also causes rivers or streams beyond the dam to shrink or dry up. On other occasions, a broken dam will cause rivers or streams beyond the dam to suddenly grow, flooding the surrounding area. In both of these scenarios, the natural environment is irreparably altered.

In the twenty-first century, numerous climate scientists cited climate change as a likely source of increased flooding. Flooding, like all natural disasters, is affected by numerous factors so determining the exact influence of climate change on it can be difficult. Nevertheless, scientists have found that human-caused climate change is causing flooding throughout the world to occur more often and be more severe. Furthermore, several scientific studies, including one published in Earth’s Future in 2022, indicated that flooding could become more frequent and occur in more places because of climate change.

Effects of Floods

Floods have devastating effects on many human-made structures. They quickly erode pavement, destroying roads and impeding the transportation of emergency personnel. They destroy homes, bridges, and farmland. Damaged infrastructure costs large sums of money to repair and replace, putting a huge strain on local economies. Additionally, floods sometimes deposit large amounts of chemicals and debris back into the water table, polluting and damaging the balance of the local ecosystem.

In some ecosystems, floods are predictable, periodic occurrences. In these circumstances, floods are often good for the environment. River soil is naturally filled with nutrients, making it perfect for growing many crops. Annual floods deposit river soil over farmlands, allowing farmers to reliably grow extremely healthy plants. One example of this phenomenon is the Nile River. The Nile floods around the same time every year. Egyptian farmers rely on the Nile flooding to fertilize their farmlands and irrigate their crops.

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Connections: Johnstown Flood

The 1889 Johnstown flood was perhaps the most devasting flood in American history. The disaster occurred in the town of Johnstown, Pennsylvania, which was located just fourteen miles downstream from the South Fork Dam on the Little Conemaugh River. On May 30, 1889, a prolonged period of heavy rains over the Johnstown region caused a spillway at the South Fork Dam to become irreparably clogged. The next day, this clog caused the dam to burst and send all the water from the humanmade Lake Conemaugh rushing toward Johnstown. The resulting flood destroyed the town and killed more than 2,200 people. The destruction was so great that it took five years to clean up the rubble and rebuild Johnstown.

Flood Prevention

Engineers have discovered a variety of ways to combat destructive flooding. For example, in coastal areas governments may construct seawalls or other barriers. People often construct these barriers in areas prone to large waves. These walls allow only small waves to pass, preventing large waves from flooding the beach and minimizing the impact of unusually high tides. Other cities prone to flooding build large barriers called retaining walls. People build these walls above riverbanks and shores, providing an additional defense against floodwaters. People construct some retaining walls so that they redirect water into nearby lakes. Others are heavily reinforced to hold back massive amounts of water. Many communities plant large amounts of grass, trees, and shrubs to help combat flood damage. Floods tend to carry away large amounts of soil, making it difficult for the environment to recover after the floodwaters recede. Bunches of roots hold the soil in place, reducing or eliminating erosion.

Levees, or dikes, are also used to protect infrastructure and property against floods. Levees are human-made structures, usually made of earthen materials. They are built parallel to bodies of water, most often rivers, and are designed to contain or divert the flow of water to provide protection. Natural levees of grass, trees, and other vegetation form around lowland rivers and streams, acting as barriers and helping to protect against rising waters.

Source Citation

Source Citation   

Gale Document Number: GALE|YFKVRX938940844