Thursday, April 17, 2008

EJ, St. Charles levees' strength in question

Study shatters faith in levee strength

Substantial work planned in East Jeff

Despite withstanding Hurricane Katrina and being poised to become the area's first levee to reach the vaunted 100-year storm elevation, the East Jefferson lakefront levee might not be adequate and may need to be totally rebuilt or substantially enlarged.

Stunning new data spit out by a complex geotechnical computer model has concluded that lake levees in East Jefferson and St. Charles Parish could be at risk for catastrophic failure.

Though Army Corps of Engineers officials said some experts doubt the accuracy of the new analysis, the agency intends to identify and implement solutions -- which could range from entirely rebuilding the levees to constructing a huge rock jetty in front of them.

"Our new method of analysis has given us (data) that we don't intend to ignore," said Lt. Col. Murray Starkel, deputy commander of the corps' New Orleans District.

Because the corps is under the gun to provide an improved hurricane protection system by 2011, officials said they can't wait for the results of additional studies that might ultimately debunk this new finding of the "Spencer's method" analysis.

"There will come a point at which we go forward with (contracts), even if they produce an overly conservative design," said geotechnical engineer John Grieshaber, technical support chief for the corps' Hurricane Protection Office.

"We will award contracts to meet that 2011 date, and if we find out later that we can do with a less conservative design, we can modify a contract in the field," he said.

Design standards updated

The computer-generated data, which blindsided even those engineers overseeing planned improvements to the region's hurricane protection system, are the result of applying more conservative design standards adopted since Katrina.

Key to that corps effort to ratchet up reliability, complex computer software was specially adapted over the past year that enabled the Spencer's analysis to identify any type of failure that could possibly occur in tricky south Louisiana soils.

As recently as January, engineers overseeing planned improvements to the East Jefferson lakefront predicted that it would be the first to attain the new elevations needed to help provide a stepped-up 100-year level of storm surge protection by 2011.

But the very next month, the Spencer's software began unspooling the news that it had identified a failure potential not detected by previous computer analyses in the Lake Pontchartrain levees of East Jefferson and St. Charles Parish.

"No, we absolutely did not expect this result," Rich Varuso, geotechnical chief for the district's engineering division, said of the geometry-based calculations that resulted.

Improving stability

In response to the Spencer findings, a team of consulting engineers already are analyzing methods of providing additional stability in the two areas that have been red-flagged.

In both cases, the deficiency stems from the size of geosynthetic materials -- heavy-duty fabrics, often made of polyester or polypropylene -- that were buried beneath the levees and berms to help stop levees from moving and failing.

Because the materials were used primarily in East Jefferson and St. Charles Parish, corps officials said the dilemma appears limited to the two parishes.

Spencer's analysis concluded that the geosynthetic material currently in place is about 20 feet too short to prevent the kind of "rotational failure" that the stuff is designed to prevent.

The previous analysis, called Method of Planes, or MOP, did not identify such a failure potential, Varuso said.

Varuso and Starkel say no earthen hurricane protection levee has ever suffered a rotational failure, which generally occurs when levee movement creates a crack near the crown and total collapse follows.

Experts disagree

Varuso said geotechnical engineers who have reviewed Spencer's geometry-based calculations at the lakefront disagree on whether they are valid findings or a fluke created by reconfigured software.

"Some experienced engineers in this field say there's no way that this (kind of failure) can happen under these circumstances, that physics won't allow it .¤.¤. and other experienced engineers feel that it could happen," he said.

Varuso said the new findings already have been passed along to other corps districts and some academicians for their opinions, and additional in-depth analyses and testing are being planned. Those findings will then be peer-reviewed by experts outside the agency.

But for now, Varuso and others said the corps can't wait for those results to endorse or debunk the findings.

"We're going to consider that it's legitimate, valid, until our own studies show otherwise unless they show otherwise," Varuso said.

Corps decision-makers said they will take no chances: If the calculations turn out to have been wrong, Starkel said, the corps's path of prudence will result in an overdesigned protection system for the two parishes.

"Is this really an issue we need to be concerned with, or is it an anomaly?" asked Starkel. "We're going to err on the side of caution and proceed with our evaluation of designs to address it. .¤.¤. We're being uber-conservative."

Although levees and floodwalls throughout the region are being reassessed using Spencer's method, it is the geosynthetic fabrics located mainly in East Jefferson and St. Charles that threw up the red flag.

"I don't think it's going to be a major factor anywhere else, but we'll have to see when the (complete analysis) is finished," Starkel said.

Each of the options being evaluated would alter the face of the lakefront in varying degrees, just as each will have varying effects on the environment and the neighborhoods that nestle up to the levees.

"We well understand the impact that expanding the footprint of the levees will have on humans and the environment," Starkel said. "Our goal has always been to design more robust levees in the same footprint if at all possible."

Starkel said all the alternatives will be publicly aired in a variety of venues once the geotechnical team finishes its analysis, possibly in June.

The options also will be included in Independent Environmental Reports, due out later this year, that will identify the corps' preferred method of addressing the stability issue.

Options to fortify the levees in East Jefferson and St. Charles include degrading the existing levees to bury and anchor wider lengths of the heavy-duty geosynthetic fabric, then rebuilding the levees. During hurricane season, no more than 300 feet of levee would be degraded at any one time.

Another option is ignoring the use of geosynthetic fabric and instead enlarging the levees and berm.

In East Jefferson only, additional options include building a large rock breakwater on the wave berm or even replacing the earthen levees with a floodwall.

Length of construction is particularly dicey against the backdrop of providing a higher level of protection by 2011.

"I would suggest to you that is a sacred date, and there will be protection by then," Grieshaber said.

Starkel said it's too soon to estimate additional costs, but said the corps hopes to mine any extra money needed from the contingency and escalation dollars built into the 100-year budget.

Ironically, the use of geosynthetic fabric was a concept pioneered in the New Orleans district, Varuso said, as a way of strengthening levees in highly developed, urban areas where right of way is at a premium.

"If we follow that (Spencer's) analysis, we're talking about drastic changes in EJ," Grieshaber concluded. "Maybe we'll end up getting information that allows us to tweak things so that the solution won't be as drastic as those (now) being considered.

"But at the end of the day, there will have to be some type of change out there, and we're not just going to add more (dirt) to the top of the levee," he said. "That won't do it."