Errrrm, levees are made with clay.
There's no way that an object as large and heavy as a barge could be drawn towards a levee by a force as insignificant as seepage...., wind forces more likely but winds had died down by the time the levees breached.
At high water levels (I live two blocks from the Mississippi River between Baton Rouge and New Orleans) levees may indeed pass water as I've been witness to such events as water bubbling through at the base at ground level and have actually seen the MR levee topped by the river just 5 miles south in White Castle Louisiana but in no way have I ever seen clay "washed away from the inside"....
TS
Yes, they are, mostly. They also contain less effective fill materials that "somehow" managed to be used.
There's no way that an object as large and heavy as a barge could be drawn towards a levee by a force as insignificant as seepage...., wind forces more likely but winds had died down by the time the levees breached.
Of course it could, if the right combination of timing and circumstances ocurred. If the barge happened to be drifting by in close enough proximity to the levee at the same time the increasing erosion due to the underground water flow increased dramatically just prior to a collapse of the surface portion of the levee, it would easily pull the barge along.
You can demonstrate this yourself. Take a plastic bucket, fill it with water and place a large fishing bobber in the center. Then take a knife, cut a large hole in the bucket about two inches below the surface of the water, and watch where the floating bobber goes.
At high water levels (I live two blocks from the Mississippi River between Baton Rouge and New Orleans) levees may indeed pass water as I've been witness to such events as water bubbling through at the base at ground level and have actually seen the MR levee topped by the river just 5 miles south in White Castle Louisiana but in no way have I ever seen clay "washed away from the inside"....
I'm glad you and your family have come through this tragedy safely. I'm not a native, but I have spent a lot of time in Lousiana, and I'm familiar with the area between BR and NO. I have also witnessed the same type of water seepage through a levee wall as you describe. The difference is, however, that although we both have been fortunate enough to not be present when that seepage has increased to a degree sufficient to cause a levee failure, it does indeed happen, and even clay does "wash away from the inside".
I want to be very clear that until this morning I've been basing my analysis of this solely on my personal experience and my understanding of the underlying science. I'm not a hydro-engineer (although I have occasionally stayed at a Holiday Inn Express).
I also want to be very clear that I'm not insisting that the barge/levee scenario I've outlined is absolute fact. There are too many unknown variables, and unfortunately we don't have an actual video record of the incident. The timing of the various possible factors could make a significant difference in the final assessment. I just believe my scenario is more likely.
That said, my instinct is to defer to the knowledge and assessments of experienced people who actually live in the affected area, so before writing this reply I did a little research to see if I could find some other information. This morning I found the following August 31st Wall Street Journal article. I hope you'll find this helpful:
http://www.post-gazette.com/pg/05243/563080.stm
"New Orleans' levee system has been key to survival"
Wednesday, August 31, 2005 By Ann Carrns and Betsy McKay, The Wall Street Journal
excerpt - "Levees may resemble earthen dams, but are not as strong. Unlike dams, which are considered "permanent" structures, many levees are engineered to withstand strong flood pressure for only a few days at a time, said Mr. Rogers. That could call into question the durability of the levee running the full length of the northern edge of New Orleans, where the waters of Lake Pontchartrain are lapping near the top."
"Levees built by the federal Army Corps of Engineers, which took on a major flood-control role after the 1927 deluge, are typically engineered to high standards and are quite strong. Most levees along the main Mississippi River channel are federally constructed. But in some areas, including around Lake Pontchartrain, some levees were built privately or by local governments and may not have the same degree of engineering."
""Those are the kind that break," said Mr. Rogers, noting that in a 1993 Mississippi River flood in the Midwest, only 17 of 79 levees that failed were federally built.
"It is rare for floodwaters to "overtop" levees, as they usually succumb first to "under seepage," in which water seeps underneath from the river side and emerges on the land side. Sometimes the severe pressure causes soil within the levee to liquefy in a phenomenon known as "sand boils," which often precede structural failure." - end excerpt