Importance of Flood Levees

flood leveeKnown as a dike in European countries, a levee is basically a flood bank or slope that runs parallel to a river. Either natural or man made, a levee helps protect an area from being flooded by serving as a protective dam or wall to the rising river during heavy rains. 

However, there are times when levees fail. Sometimes the water from the river is so strong that an actual part of the levee breaks resulting to a whole where the flood water rushes in. This kind of levee failure is referred to as a levee breach and is considered very dangerous. At times water from the river flows over the levees causing massive flooding on the other side. The problem with levee overtopping is that it causes further damage to the levee which can lead to a complete breach.

In the US, most of the levees across the country were manmade, having been constructed for both agricultural and flood protection purposes. A lot of the levees are old with some are even more than centuries old. Early this year, the US Army Corps of Engineers reported that 146 levees in the US were already in a sad state and are at risk of failing if a major flood occurs.

In 2005, the country saw the devastating effects of levee failure when Hurricane Katrina passed through New Orleans. The rains brought by the storm resulted to more than 50 levee breaches and water overtopping. Almost 80% of the city went underwater as a result, caused vast damages in properties, and lost of human lives.

Other historical levee breaches include the Great Mississippi Flood in 1927 where the Mississippi River breached levees and flooded 27,000 square miles (70,000 km²) in seven states, displaced more than 700,000 residents, and killed 246 people; the 1953 North Sea flood levee breach in the United Kingdom and the Netherlands which killed more than 2,000; and the Jones Tract island levee breach in Sacramento-San Joaquin Delta which happened just a year before Hurricane Katrina.

A typical levee should be at least several feet high and wide. The advantage of a levee over a flood wall is that with a solid foundation or base, one can increase its height temporarily by stacking sandbags or water-inflated dams on it.

When building a levee, it is important that the sloping surface be protected from erosion. To prevent, this engineers plant the slopes with grass or shrubs. Also, aside from erosion levees can have problems with burrowing animals and tree roots. The integrity of the base is compromised with tunneling from the animals which increases the risks of breach.

Moreover, you need to understand that a levee may very well keep the rising river from flooding an area but in cases where overtopping occurs, the levee becomes an enemy as well. When the area becomes flooded, the levee traps the water inside the levee.

 
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