A floodplain is an area of land which is covered in water when a river bursts its banks. Floodplains form due to both erosion and deposition. Erosion removes any interlocking spurs , creating a wide, flat area on either side of the river.
During a flood, material being carried by the river is deposited as the river loses its speed and energy to transport material. Over time, the height of the floodplain increases as material is deposited on either side of the river. Floodplains are often agricultural land, as the area is very fertile because it's made up of alluvium deposited silt from a river flood.
In emergencies, temporary levees can be made of sandbags. These soak up the water and usually prevent excess water from seeping past the sand. Artificial levees prevent flooding. But they also create a new problem: levees squeeze the flow of the river. Water levels are higher and water flows faster. This puts more pressure on levees downstream and makes the water more difficult to control.
If levees break, it also makes containing the flood more difficult. Since the 18th century, levees have protected Louisiana and other nearby states from flooding by the Mississippi River. When Hurricane Katrina struck New Orleans in , the levees could not withstand the storm surge.
The levees broke, and water flooded 80 percent of the city. Although most levees exist to control rivers, they can also exist on the coast. The country of the Netherlands has an elaborate system of dikes, levees, and dams to hold back the North Sea.
Land for farms, industry, and residential use has been created from land that was once the ocean floor. The Bay of Fundy, which borders the provinces of New Brunswick and Nova Scotia, Canada, has one of the highest tidal ranges in the world. The tidal range reaches more than 17 meters 55 feet in some places. To make the most use of land that would otherwise be underwater during high tide , Canada has constructed levees along parts of the Bay of Fundy.
The levee system along the Mississippi River has some of the longest individual levees in the world. One of these levees stretches south along the river from Pine Bluff, Arkansas, for an entire kilometers miles.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Of that, only about 1. Most of our drinking water comes from rivers and streams. This water is the lifeline of ecosystems around the world. Freshwater is a precious resource on the Earth's surface.
It is also home to many diverse fish, plant, and crustacean species. The habitats that freshwater ecosystems provide consist of lakes, rivers, ponds, wetlands, streams, and springs. Use these classroom resources to help students explore and learn about these places. Floods are events where water overflows onto land that is typically dry.
This can occur when there is a large amount of rain, rapid snow or ice melt, a blast of water onto a coastline during a storm, or the failure of manmade infrastructures, such as dams or levees. Floods are among the most expensive and frequent natural disasters in the United States, and as the impacts of climate change are more acutely felt, floods are expected to worsen.
Many species depend on the floodplain for spawning and successful survival and growth of the young. These may be able to find alternative sites in backwaters and slack areas of the channel but such sites are less abundant than the area of the floodplain, and the species will often decline. Species that pass their whole lives on the floodplain are also adversely affected because the annual flood event needed to maintain the floodplain water bodies no longer occurs. Many invertebrate migrate downstream with the drift, and fish in tropical rivers have eggs, larvae and young that also drift with the current.
The timing of the development of the eggs and larvae is closely linked to the current speed so that the young fish arrive at the floodplains at the right time in their life cycle.
Acceleration of the current accelerates the speeds at which insects drift downstream and they may be carried well past suitable sites for colonization when they settle. Similarly the young stages of fish can be carried past appropriate nursery areas and even out to sea. In either case the young fail to develop and die.
Polders -- Polders are levees that have been extended to completely enclose an area of floodable land. Polders are generally constructed to reclaim land for agriculture although they may also be used to protect urban sites.
In rice growing areas such as the Mekong, the function of the polder is not to completely exclude water but to gain better control of the depth and duration of flooding to maximize yields of rice and other water dependent crops.
Therefore, polders are equipped with sluice gates that can control the rate and volume of water entering the polder.
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