Why are levees used

People have been building and reinforcing levees since the beginning of civilization. Farmers were able to grow crops like cotton and rice. In addition to creating living space and cropland, levees can also provide a measure of protection from invaders.

Levees can make a river like a moat , preventing people from easily invading territory on the other side. Destroying levees can also stop invading forces. In , Chinese leaders intentionally broke levees on the Yellow River to prevent the Japanese military from advancing. More than , people, Japanese and Chinese, died in the resulting flood. Artificial levees need to be protected. They have to stand up to erosion , or wearing away, by the nearby water.

Sometimes, trees and plants like Bermuda grass are planted near levees to anchor the soil. Engineers need to maintain levees with structural work to reinforce the boundaries. 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. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

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Levees may require underground extensions to prevent seepage through the soil, depending on soil type, water depth and flood duration. You must provide drainage for rain that falls inside the levee system when it's NOT flooding and when it IS flooding. It's very hard to add drains once the levee is built, so make sure the number, size and locations are right before you pile on the dirt.

A pump is needed inside the protected area. Water can seep under or through the levee, and rain will fall on the inside. You have to pump it out during a flood. Placing the levee closer to the building may reduce your dependence on pumps. Levees have natural enemies: burrowing creatures and tree roots.

Check your levee each year for signs of tunneling. Check with the local building or permit office to see if a permit is required. Some communities review plans to be sure the levee will not interfere with drainage and will not diminish flood storage capacity in violation of local law. Avoid damaging underground gas, water and electrical lines or your sewer line during construction. When water goes over the top or breaks a levee, the protected area may fill with water rapidly.

Engineers built the levee system with the goal of creating a system that could stand up to the worst storm possible in years.

Unfortunately, the study greatly miscalculated how powerful potential storms could be. Riskier design : New Orleans' levees were built to sustain the city's growth, unlike the levees in neighboring areas, which were built to provide safety.

As a result, New Orleans' levees were shorter and weaker. Safety compromised by bureaucracy : No central agency was in charge of maintaining the levees. This task instead fell to several different private firms and government agencies, leading to communication problems and the breakdown of various upgrade projects.

Poor maintenance : Levees require constant upkeep. As the land in New Orleans sinks, so do the levees. Investigators also suspect that large trees growing nearby undermined the levees. Insufficient funds : The U. Army Corps of Engineers, which oversees the design and construction of levees, had been hit by budget cuts. This left the agency with fewer experienced engineers.

Dikes of the Netherlands " ". The windmills of Holland pump water from behind the dikes and back out to sea to keep the land dry. Thinking long term : While the team of engineers in New Orleans tried to build levees strong enough to withstand the strongest possible storm in years, Dutch engineers designed a system strong enough to match the kind of catastrophic storm that only occurs once in 10, years.

Less reliance on solid barriers : Instead of constructing increasingly bigger barriers like levees and floodwalls, Dutch engineers have sought to create better ways of absorbing floodwaters in marsh plains and specially constructed rivers.

In some cases, this even involves setting dikes farther back from the water. New textiles : The Dutch also developed tough, synthetic textiles to better anchor earthen levees. These prevent soil movement and water penetration. The New Orleans levee system began using this technology following Hurricane Katrina. Better monitoring systems : In addition to commanding more stringent, centralized control and maintenance of their dikes, the Dutch also use automated surveillance systems to keep an eye on how their levees are holding up.

They installed fiber-optic and electronic sensors in dike structures to report changes back to a central monitoring station. Several other systems monitor water pressure and water level. June Gonzales, John Moreno. Storm memorial delayed.