With the exception of a few flat ridges running from north to south, it is so low that it requires, to protect it from overflows, an unbroken line of levees averaging 15 ft.
Nearly all of this vast flood-plain lies below the level of high water in the Mississippi, and, but for the protection afforded by the levees, every considerable rise of its waters would inundate vast areas of fertile and cultivated land.
Of Mississippi river levees, within the state, was built almost entirely after 1866, and represents an expenditure of about $43,000,000 for primary construction alone; of this sum, the national government contributed probably a third (the state expended about $24,000,000 on levees before the Civil War).
Some of the levees, especially those in swampy regions where outlet bayous are closed, are of extraordinary solidity and dimensions, being 20 to 40 ft.
The task of maintenance consists almost entirely in closing the gaps which occur when the banks on which the levees are built cave into the river.
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