Public Service

Big Hurt in the Big Easy

A team of Berkeley engineers pokes through Katrina’s rubble in search of clues that could help prevent flooding the next time a Category 4 hurricane hits.

By Robert Sanders

Ray Seed (in Cal cap) and Bob Bea (hatless) prepare to drive the New Orleans levees with colleagues from ASCE and the Army Corps of Engineers. Rune Storesund photo

Fall 2005 | It’s hard to pull your eyes away from the mud-encrusted homes of New Orleans’ Ninth Ward. Splintered or partially collapsed houses stretch as far as the eye can see, amid a shallow sea of dark-gray mud already dried and cracked into jigsaw-puzzle pieces. Dirty, rusting cars line the streets at odd angles; overhead wires dangle threateningly into the street; awnings creak in the breeze. An eerie silence emanates from the deserted streets, disturbed only by the occasional burr of a cicada or a bird chirping from the ravaged trees.

And scattered everywhere is the personal flotsam of people’s lives—the jumbled mattresses, the clothing, the portraits of children in graduation robes lying in the dried mud, and the now-homeless teddy bears and dolls.

But we are here to look at the levees, not the damage the levee breaks caused. Ray Seed, a Berkeley professor of geotechnical engineering, assembled a troop of engineers that touched down in New Orleans on Oct. 2 — a month after Hurricane Katrina spun into the area — to investigate the levee failures that devastated the Ninth Ward and many other neighborhoods of the city.

“The evidence is disappearing as we speak,” Seed said after a week on the ground. “Some things we saw early in the week are already buried as they rebuild the levees.”

One step ahead of the bulldozers
To recover and record this ephemeral evidence quickly, Seed and his Berkeley team, with funding from the National Science Foundation (NSF) and the campus’s Center for Information Technology Research in the Interest of Society (CITRIS), joined teams mobilized by the American Society of Civil Engineers (ASCE) and the U.S. Army Corps of Engineers. Their charge was to visit as many of the damaged or destroyed levees and floodwalls as possible. During their week on the ground, they surveyed a large portion of New Orleans’ 370-mile-long system of levee and floodwall defenses, focusing primarily on the breaches that flooded major parts of the city, and on the heavily hit levee bordering the Mississippi River Gulf Outlet.

They reached the scene none too soon. The New Orleans District of the Army Corps was rapidly repairing the levee and floodwall breaks to protect against storms that could strike during the remainder of the hurricane season. In the short time Seed’s team was in the city, bulldozers completed a neat flattop of gravel on the patch at the Industrial Canal breach that flooded the Ninth Ward. Everything in the breach — sand bags, debris, and clues to why the levees failed — was being buried under dirt, stone, and gravel.

ASCE geotechnical team members inspect a portion of the floodwall along the Industrial Canal that was overtopped and flattened by Katrina’s storm surge. The force of the storm shattered much of the concrete wall that topped the steel sheet piles. Rune Storesund photo

The once-vertical sheet piles beneath Seed’s boots were identical to those that form the foundation for all the floodwalls topping the miles of earthen levees that provide New Orleans with additional protection from high tides and storms. The sheet piles are essentially interlocking steel slats pounded along the entire length of the levee embankments, then encased in concrete. These steel-and-concrete floodwalls have been a crucial part of the vulnerable city’s levee system since Hurricane Betsy made landfall in 1965, doing substantial damage. The system was subsequently strengthened to withstand a Category 3 hurricane, judged to be a once-in-every-200-years event.

Katrina, of course, was the dealbreaker. When it struck New Orleans, it was a Category 4 storm lumbering northward across nearby Lake Pontchartrain. Though it didn’t strike the city dead-on, Katrina’s winds piled Pontchartrain water along the hurricane’s margins in a destructive surge that tossed yachts into one another like bowling pins.

Though most of the Pontchartrain levees survived, the weak links were two of the canals that drain the city (the 17th Street and London Avenue canals) and the Industrial Canal that links the Mississippi with the lake and the Intracoastal Waterway. Pumps constantly pull water from city areas below sea level and dump it into the canals, which drain into the lake. The Katrina surges funneled water up these canals and pushed the floodwalls aside in three areas. Once they were breached, the water poured in to submerge nearly the entire city.

The Berkeley team and the ASCE engineers concluded that the Industrial Canal levee that failed in the early hours of Aug. 29 was simply overwhelmed and overtopped by walls of water from Lake Pontchartrain. The floodwaters pouring in from the Industrial Canal, coupled with a 24-foot wall of water surging across the bayous from the east, pinched the primarily African American Lower Ninth Ward, the poorest region of the city.

“It’s as if God targeted the Ninth Ward,” Seed said.

Levees and banana peels
The Corps initially thought that all the failed levees had been overtopped by the wall of water pushed ahead of the hurricane. Seed and Peter Nicholson, head of the ASCE team, announced, however, that their evidence pointed to the failure of two levees — alongside the 17th Street Canal at Robert E. Lee Blvd. and the London Avenue Canal at Mirabeau Bridge — without overtopping.

The team ascribed these two breaches to soil failure at the base of the levees. Acknowledging that levees are, by definition, built on poor, marshy soils, Bea noted that weak soils associated with a peat layer at the base of the levee likely allowed the levee and wall at the 17th Street Canal to slide laterally by about 35 feet, “like stepping on a banana peel.”

Seed, Bea, and Nicholson cautioned that the poor soil still underlying the patched levee needs to be taken into account as the levee is repaired.

Both the Berkeley and ASCE teams plan more data collection, testing, and analysis before they can determine and report on precisely why each levee performed as it did. Their recommendations “will help provide future protection for the residents of New Orleans and elsewhere in the nation,” Seed said.