NEW ORLEANS -- As investigators and residents have picked through the battered New Orleans levee system's breaches, churned-up soil and bent sheet pile in the months since Hurricane Katrina struck, they have uncovered mounting evidence that human error played a major role in the flood that devastated the city.

Floodwall breaches linked to design flaws inundated parts of the city that otherwise would have stayed dry, turning neighborhoods into deathtraps and causing massive damage. In other areas, poorly engineered gaps and erosion of weak construction materials accelerated and deepened flooding already under way, hampering rescue efforts in the wake of the storm.

These problems turned an already deadly disaster into a wider man-made catastrophe, and have made rebuilding and resettlement far tougher and more expensive challenges.

That's the picture that emerges from investigations of the levee system by teams sponsored by the Louisiana state government, the American Society of Civil Engineers and the National Science Foundation, as well as dozens of interviews with local residents, officials and engineers.

Experts say the New Orleans flood of 2005 should join the space shuttle explosions and the sinking of the Titanic on history's ill-fated list of disasters attributable to human mistakes.

The evidence points to critical failures in design and construction, as well as a lack of project oversight and responsibility that allowed small problems to metastasize into fatal errors. Twisted lines of authority led to cursory inspections, communications snafus and even confusion over such basic information as wall dimensions.

Outside engineers, political leaders and many New Orleans residents now question the judgments and even the once-unassailable competency of the Army Corps of Engineers, which had final authority over the system. The corps and some of the same firms involved in the original design and construction are spearheading the current effort to repair the system and already planning to build stronger protections.

Sen. David Vitter, R-La., who sits on two Senate committees investigating the levee failures, says the U.S. system for building flood defenses is broken. The corps, he said, should be overseen by outsiders who can assure it will do the job right.

"We need a new model, a new structure, a new process to get this done which has to include outside, independent review of the corps by outside, independent engineering experts," he said.

The levee flaws also raise troubling questions about the integrity of flood defenses elsewhere.

"Everybody who has a levee out the back door now has to look out and wonder, is this going to fail? Was it designed right?" said Steve Ellis, vice president of Taxpayers for Common Sense, a Washington fiscal watchdog group critical of the corps' priorities.

Corps spokesman David Hewitt said the agency has multiple experts and engineers from outside agencies, private firms and academia to aid its investigation. "We are determined to find out exactly what happened both in the technical engineering and the planning and execution process so that we can prevent another occurrence," Hewitt said. "We are engaging the best minds and professional expertise in this important effort."

Engineers say that most structures that fail do so not because they're hit by overwhelming forces, but due to flaws that creep in unnoticed during design, construction and upkeep. A paper published this month by Robert Bea, an engineering professor at the University of California at Berkeley who is studying the levee failures, concluded that 80 percent of 600 structural engineering failures he studied over the past 17 years were due to "human, organizational and knowledge uncertainties."

Bea said everything he has seen about the New Orleans levee system so far tells him it belongs in that category.

The levee system's overall design dates to the 1950s, when understanding of hurricane risks and flood dynamics was primitive compared to today. The system was never built to take a hit from the most powerful hurricanes -- storms in Categories 4 or 5 on the Saffir-Simpson scale. The levees were designed by congressional mandate to fend off floodwater heights -- up to around 11 or 13 feet, depending on location -- that Category 1, 2 and some Category 3 storms would kick up.

But the investigations show that it did not even live up to that billing. When Katrina's storm surge rolled in from the Gulf of Mexico before dawn Aug. 29, the huge dome of water washed over levees on the southeast side of New Orleans and flowed into the heart of the city via two waterways. Some flooding was inevitable in those areas, as evidence shows the water flowed over the tops of the levees.

Later that morning, as surge water rose in Lake Pontchartrain, which is linked to the Gulf, floodwalls along the 17th Street and London Avenue canals breached, even though water was well below their tops. Investigators say those breaches shouldn't have happened.

Investigators say the walls broke when floodwater, pushing through the soft, porous earth under the steel sheet pile foundations, started moving the soil. The flood inundated much of central New Orleans over the course of the day and night.

Engineers say some systemic design problem caused the breaches -- not merely a localized fluke -- because walls gave way in two canals and some appear to have been close to breaching at other points.

"There does appear to be a systemic failure along the drainage canals because the failure occurred at two places simultaneously," said J. David Rogers, a geotechnical engineer at the University of Missouri-Rolla who studies levee failures. "There's got to be something big that's causing that. ... This is a very bad failure mark. It's telling you they missed the mark by a country mile on the design."

While it's always easy to second-guess after a disaster, outside engineers say that the depth of the sheet pile foundation appears too shallow. A survey by Team Louisiana, the state-sponsored forensics group, found -- and the corps confirmed last week -- that the sheet pile depth was about 10 feet below sea level in the breached areas at both canals, much shallower than the 18.5 feet-below-sea-level depth of the canals and seven feet shorter than the corps thought.

Modjeski & Masters, the firm that designed the 17th Street canal wall, said last week it had initially recommended a 35-foot depth for the piling on the 17th Street canal, then shortened it at the corps' behest, but offered no documentation to back the claim.

It's still unclear exactly what went wrong, though engineers suggest the soil's resiliency was overestimated.

New Orleans soil is swampy and mushy, with alternating layers of peat, clay and sand. Over the length of a floodwall it varies wildly in consistency and strength.

"Those are the kinds of subsurface conditions that lend themselves to having weak pockets or stronger pockets, and Mother Nature will always find the weak pockets," said Joseph Wartman, a Drexel University geotechnical engineer studying the levee failures. "What makes levee design and engineering so challenging is you can have a system that's many, many miles long and you only need the weakest 150 feet to rupture for the whole system to fail."

Another related factor in the breaches -- one with national implications -- is the relatively low safety factor used in construction of the levee banks and floodwalls. A safety factor is a kind of cushion that engineers include in a structure's design to ensure it can withstand all the punishment it's designed to take, plus a little more.

Corps standards for levees and floodwalls date back decades, officials say, and were originally intended to protect sparsely populated rural areas, not cities and billions of dollars of valuable infrastructure. The safety factor of 1.3 used in the designs is significantly lower than those used in structures with similarly large-scale tasks of protecting lives and property.

With data from soil borings spaced at more than 300-foot intervals along the canals, engineers could develop only a fragmentary picture of what is underground. They were supposed to account for that uncertainty. That's typically done either by raising the safety factor or by making conservative estimates of soil conditions.

Team Louisiana investigators said last week that based on new calculations, they believe engineers working for contractors Eustis Engineering and Modjeski & Masters miscalculated the depths of the 17th Street canal walls. The team has not yet released detailed findings. University of California engineers say the designers may not have accounted for storm surge water's effects on the soil.

According to project and court documents, those designs were reviewed and approved by corps engineers.

It's not clear yet if additional factors such as cost-cutting or specific on-site construction problems contributed to the levee breaches, but the failures can also be linked to a chain of political and managerial decisions.

The corps originally proposed building floodgates at the mouth of each canal to block surge waters. But local officials insisted on building floodwalls because floodgates would have made it difficult to pump water out during a storm. Engineers say the obvious -- though expensive -- solution is to build pumping stations at the lakefront rather than miles inland.

A 1980s-era dredging project in the 17th Street canal adjacent to the breached area left the levee wall much narrower than it was on the unbreached side. Investigators say that change probably contributed to the ultimate failure of the wall.

Pittman Construction, the contractor that built the 17th Street wall, ran into trouble driving sheet piles in 1993. When the concrete tops to the walls were poured, documents show, the walls tipped slightly. Though the corps attributed this to Pittman's methods, not the site conditions, and a judge agreed, some engineers say the difficulty they encountered was an early warning sign.

Meanwhile, state and local officials have admitted they generally skipped the canal floodwalls in annual inspections of levees -- and the levees they did inspect were examined in a cursory fashion.

To the east, where water flowed over levees, assessing the system's performance is a more complicated task. In general, engineers say that once a levee is topped, its structural integrity cannot be guaranteed. But many walls breached or eroded as well. That and the large scope of the damage have alarmed investigators. Levees protecting St. Bernard Parish and the Lower Ninth Ward -- areas still mostly uninhabitable -- were all but washed away by the storm, for example.

One source of the scouring and multiple breaches is actually a corps policy, dictated by Congress. Corps officials say they are not allowed to put rip-rap, concrete or other forms of scour protection on the dry side of levees. Doing that anticipates flood levels higher than the walls are designed for, which is beyond the corps' mandate for Category 3 protection.

A report published last month by the American Society of Civil Engineers and National Science Foundation teams identified other unanticipated weaknesses in the levee system. Builders used weak, sandy soils in the now-obliterated St. Bernard Parish hurricane levee, and that likely contributed to its rapid destruction. In areas where two different levee sections came together, investigators found many awkwardly engineered transitions that allowed water through.

A much larger problem lies in the overall design of the levees along the city's southeastern flank. Unlike areas fronting Lake Pontchartrain, southeastern areas are more or less directly exposed to waters from the Gulf, and hurricane floods are more likely to strike there and rise higher when they do.

The levee system forms a V-shape where two waterways meet that acts as a giant funnel, driving water heights even higher and channeling storm surge directly into canals leading into the city.

Computer modelers have complained for years that the corps had underestimated the risk to those areas, and former corps modeler Lee Butler estimated the actual risk was double the corps estimate in a 2002 study done for The Times-Picayune of New Orleans. The corps only recently announced it would stop dredging the Mississippi River-Gulf Outlet, a controversial, little-used navigation channel linked to the high storm surges.

It will takes months, and possibly years, to arrive at a detailed assessment of what went wrong and assess responsibility, engineers familiar with the situation say. Investigators must not only determine why individual wall sections failed, they must trace the roots of decisions, untangling overlapping responsibilities of the corps, private contractors and local agencies. A federal inter-agency team investigating the system won't make its report until next June. A National Research Council team is only now being formed.

So far, the scope of the disaster and the human element central to it have only begun to sink in among political leaders and agency heads, including the corps, which is at the center of all the inquiries. The corps has declined comment on the causes of the levee failures, pending the outcome of its own studies.

People familiar with the agency say that the disaster means things may never be the same.

"In the old days the corps used to get criticized for being way too conservative in their designs," said Don Sweeney, a corps economist for 22 years who left after exposing irregularities in the agency's economic impact statements and now teaches at the University of Missouri.

"They would design a structure with a safety factor of 4 or 5. They did have that reputation of building things with integrity that were built to last. And if they said it was built to do something, it would do it."

Dec. 11, 2005


(John McQuaid, Bob Marshall and Mark Schleifstein are staff writers for The Times-Picayune of New Orleans. They can be contacted at john.mcquaid@newhouse.com, bmarshall@timespicayune.com and mschleifstein@timespicayune.com.)