<p>That damn dam ram kept butting her head against that dam. </p>
<p>For you nondirt people and engineers, Please let me clarify your thinking whether the levees of New Orleans was breached or overflowed. Please recognize the spin doctors are giving you “newspeak.” </p>
<p>Short Backround reading and illustrations:
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<p>Earthen Dams and levees are basically composed of uncemented earth. The New Orleans Levees have core of steel plate, which given the rule of thumb, is driven into the ground so that a portion of its total is below grade, and another portion above grade. This plate is maintained in place by the mass of earth on the dry side of the levee and by water pressure on the wet side. </p>
<p>When water “overtops” the structure (levee) the water erodes away the dry side earth. With the dry side earth gone, the steel plate core has lost its support and thus collapses, causing a catastropic break (breach) that unzips the levee .</p>
<p>In Dams, there usually is relief system that reduces the wetside water level, thus pressure to rebalance the structure. The relief system (spillway)is made of study material (concrete) that withstands erosion. For levees, there is no relief system and thus overtopping is a definite hazard.</p>
<p>The NO levees was built to withstand a cat 3 hurricane, which implied protection from overtopping and not from “breaching leakage”. For the most part, the levee succeeded, but as always, failure will always occur at the weakest point.</p>
<p>For anyone (4 year old) who has build a sand fort at the beach knows that the fort cannot withstand massive attacks of water and will eventually fail due to erosion of the walls from wet side, or overtopping. </p>
<p>The Johnston flood was caused a breaching of the dam when the dam was overtop. see article above. </p>
<p>The Missoula floods that created the Columbia Gorge, the Paloose, and Willamette Valley, was believed to be caused by overtopping of the glacier dams. </p>
<p>I would site our own US Gov, Corps of Engineers, US Army but dam building and construction has been removed since 9/11.</p>