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Epic flooding will test levee system as never before, experts say
<!--endclickprintinclude--><!--startclickprintexclude-->By Tom Watkins, CNN<SCRIPT type=text/javascript>cnnAuthor = "By Tom Watkins, CNN";</SCRIPT>
<SCRIPT type=text/javascript>if(location.hostname.indexOf( 'edition.' ) > -1) {document.write('May 10, 2011 -- Updated 0933 GMT (1733 HKT)');} else {document.write('May 10, 2011 5:33 a.m. EDT');}</SCRIPT>May 10, 2011 5:33 a.m. EDTMay 10, 2011 5:33 a.m. EDT
Excerpt:
Under the best-case scenario, the Army Corps of Engineers will prove able to manage the water flow and flooding will be minor. But there is little doubt that property will be lost and the economy will take a hit, Dakka said.
"On the other hand, the worst-case scenario is that the water rises, we're not able to manage it, it finds the weak areas, exploits those vulnerabilities, perhaps even segments of the river levee get taken out by erosion or collapse due to failure of saturated levees or other things could happen -- ships get loose in the river; barges of chemicals run into the side of the levee."
If levees break, weeks could pass before engineers could reseal them, he said.
But Dakka said his worst-case scenario might not tell the whole story.
"There are unintended consequences that are going to happen that we can't possibly even fathom right now," he said. "We just have to be ready for it and get people out of the way."
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How the Mississippi River levees could fail
May 9th, 2011
09:14 PMET
Excerpt:
Earthen levees should keep most of the larger towns and cities safe as an extraordinarily high volume of water runs down the Mississippi to the Gulf of Mexico. But levees can fail, in part because moving water has tremendous force. This force will try to erode, saturate, undermine and destroy everything in the way.
Most levees are piles of dirt lined along edges of a river. In theory, vegetation and its roots will keep the dirt stable as water flows by.
Levees can fail if water runs over the top ? this is called overtopping. The force of the moving water erodes the soil below, and this can cause a catastrophic breach. The erosion continues until the hole is so large that floodwaters surge into the now unprotected land.
Levees also can fail from below as the water pressure undermines the piled dirt. The water forces itself below the levee and eventually out from the bottom on the dry side of the pile. This is called a sand boil or a mud boil, because of its bubbling appearance.
Also, too many days with floodwater near the top of a levee can saturate the levee?s soil, causing a washout and breach.
Full text:
<!--endclickprintinclude--><!--startclickprintexclude-->By Tom Watkins, CNN<SCRIPT type=text/javascript>cnnAuthor = "By Tom Watkins, CNN";</SCRIPT>
<SCRIPT type=text/javascript>if(location.hostname.indexOf( 'edition.' ) > -1) {document.write('May 10, 2011 -- Updated 0933 GMT (1733 HKT)');} else {document.write('May 10, 2011 5:33 a.m. EDT');}</SCRIPT>May 10, 2011 5:33 a.m. EDTMay 10, 2011 5:33 a.m. EDT
Excerpt:
Under the best-case scenario, the Army Corps of Engineers will prove able to manage the water flow and flooding will be minor. But there is little doubt that property will be lost and the economy will take a hit, Dakka said.
"On the other hand, the worst-case scenario is that the water rises, we're not able to manage it, it finds the weak areas, exploits those vulnerabilities, perhaps even segments of the river levee get taken out by erosion or collapse due to failure of saturated levees or other things could happen -- ships get loose in the river; barges of chemicals run into the side of the levee."
If levees break, weeks could pass before engineers could reseal them, he said.
But Dakka said his worst-case scenario might not tell the whole story.
"There are unintended consequences that are going to happen that we can't possibly even fathom right now," he said. "We just have to be ready for it and get people out of the way."
Full text:
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How the Mississippi River levees could fail
May 9th, 2011
09:14 PMET
Excerpt:
Earthen levees should keep most of the larger towns and cities safe as an extraordinarily high volume of water runs down the Mississippi to the Gulf of Mexico. But levees can fail, in part because moving water has tremendous force. This force will try to erode, saturate, undermine and destroy everything in the way.
Most levees are piles of dirt lined along edges of a river. In theory, vegetation and its roots will keep the dirt stable as water flows by.
Levees can fail if water runs over the top ? this is called overtopping. The force of the moving water erodes the soil below, and this can cause a catastrophic breach. The erosion continues until the hole is so large that floodwaters surge into the now unprotected land.
Levees also can fail from below as the water pressure undermines the piled dirt. The water forces itself below the levee and eventually out from the bottom on the dry side of the pile. This is called a sand boil or a mud boil, because of its bubbling appearance.
Also, too many days with floodwater near the top of a levee can saturate the levee?s soil, causing a washout and breach.
Full text:
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