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Welcome to Brain Stuff, a production of IHeart Radio.

Hey, Brain Stuff, Lauren Vogelbaum here.

In his poem, The Dry Salvages, T.S. Eliot described the river as a strong brown god, a powerful force that while often patient and

nurturing proves itself untamable and merciless. The greatest cities in human history have risen up on the

banks of rivers and by the seaside, but in doing so, their builders chose to live in close confines with an unruly force.

Rivers have surged, washing away whole communities, or changed course, abandoning prosperous

kingdoms to the dust. Even today, ocean storms threaten to decimate centuries' worth of human

endeavor. Humans have attempted to conquer the

problems of changing water levels for thousands of years. One of the oldest weapons we've wielded

against the rivers and oceans is the levee, also known as a dyke. A levy is simply a man-made

embankment built to physically block a river from overflowing its

banks or to prevent ocean waves from washing into undesired areas. In New Orleans, for example,

the levees attempt to perform dual duties. On one side of the city, levies protect against floods

from the Mississippi River, and on the other side,

they help to keep Lake Pontch Train in place. In parts of the Netherlands, dikes stop ocean waters

from reclaiming thousands of miles of land, much of which is either at or below sea level.

The famous windmills of Holland pump water from behind the dikes and back out to sea to keep the land dry.

As in Louisiana, and for another example, the Florida Everglades region, there are parts of the

Netherlands where engineers have created new dry land with complex water management systems.

A levy is typically little more than a mound of not very permeable soil,

like clay, wider at the base and narrower at the top. But they can be a little or a lot more

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