New Orleans flood protection gets upgrade

... but not in time for next hurricane season.

- but not in time for next hurricane season.

Five months before the deadline of 1st June 2006 for restoring the New Orleans levee system to the Category 3 storm protection status it held at the time of the Hurricane Katrina onslaught last August, the White House agreed in mid-December to rebuilding the system to Category 4 standards.

The decision has of course been well received in New Orleans, where the city's Mayor Ray Nagin hailed it as a 'come home' signal to thousands of displaced residents.

But reconstruction at this higher standard cannot possibly be achieved by mid-summer and may well take several years.

Speaking to the New Orleans newspaper The Times-Picayune recently, Robert G.

Bea, one of the civil engineering professors at the University of California, Berkeley, who took part in the investigation of the levee failures in association with the American Society of Civil Engineers, said it would be possible to restore the levies to pre-Katrina strength by the start of the next hurricane season, but only if the U.S Army Corps of Engineers puts the job on something like a war-time footing.

This confirms the testimony given last November to the Senate Committee on Homeland Security by Dr Raymond B.

Seed, professor of civil and environmental engineering at the Berkeley campus, giving evidence on behalf of the Levee Investigation Team sponsored by the U.S.

National Science Foundation.

He told the committee: "The U.S.Army Corps of Engineers are stretched very thin right now, trying to respond and effect emergency and interim repairs in the wake of this catastrophe".

"It must be the job of the Federal Government, and oversight committees such as this one, to ensure that they have the resources and technical capabilities to get their job done safely and well." The message has got through to the White House and that is most encouraging.

But it is not likely that by June/July this year the ravaged city of New Orleans will have flood protection much better than that which failed last August.

And whether restoration of the levees to Category 4 status will on its own provide an answer to the ever-present threat in the Gulf of Mexico is a matter of controversy, as later submissions to the Senate Committee on Environment and Public Works revealed.

Causes of levee failures.

Dr Seed underlined the gravity of the issue when he told the Homeland Security Committee: "The levee system in New Orleans actually protects more life and property than almost any major dam in the United States".

"We recommend that the Corps should retain an independent board of consultants to review the adequacy of the interim and permanent levee repairs being carried out in the aftermath of Hurricane Katrina".

In his evidence, Dr Seed said that the storm surges produced by Hurricane Katrina flooded approximately 75 per cent of the metropolitan area of New Orleans".

"Most of the levee and floodwall failures", he said, "were caused by overtopping, as the storm surges rose over the tops of the levees and their floodwalls and produced erosion that subsequently led to failures and breaches".

"Overtopping was most severe at the east end of the flood protection system, as the waters of Lake Borgne were driven west producing a storm surge of the order of 18 to 25 feet that massively overtopped levees immediately to the west of this lake".

The immediate effect of this calamity was the rush of floodwaters towards the St".

"Bernard Parish which lies between the Mississippi and the sea".

"With the aid of photographs with which the National Science Foundation sponsored report is liberally supplied, Dr Seed showed that a six-mile section of levees facing this wall of water was swept away".

""There is virtually nothing left of these levees along some parts of this stretch." Elsewhere, a severe storm surge along the lower reaches of the Mississippi River breached the levee protecting the southern part of the Plaquemines Parish with such force that homes were carried across the narrow corridor and thrown astride the crest of the Mississippi River levee".

"Most of the failures in the central New Orleans area, he said, were the result of overtopping".

"One of the common failure modes was simply water cascading over concrete floodwalls and then carving sharply etched trenches".

"This reduced the lateral support at the back sides of the walls and left them vulnerable to the high water forces on their outboard faces".

"In the East Bank Canal District, further to the west, three levee failures occurred at water levels below the tops of the floodwalls lining two of the three drainage canals discharging into Lake Pontchartrain".

"These, said Dr Seed, were likely caused by failures in the foundation soils underlying the levees".

""Although it is somewhat customary", he commented, "to expect levee failures when overtopping occurs, the performances of many of the levees and floodwalls could have been significantly improved, and some of the failures likely prevented, with relatively inexpensive modifications of the levee and floodwall system details".

"The addition of overtopping erosion protection at the land side of the floodwalls through the provision of rip-rap, concrete splash slabs, or even paving of the ground surface at the inboard faces of the levee crest floodwalls might have been effective in reducing this erosion and might have prevented some of the failures observed." Evidence of deep structural flaws.

Meanwhile, on the ground in New Orleans, David Rogers, a professor at the University of Missouri's Rolla campus specialising in levee and floodwall engineering, told the Times-Picayune newspaper that he was not impressed by plans merely to restore a levee system that had proved so disastrously inadequate.

He said that the collapse of three levees in the East Bank Canal District without ever being overtopped was evidence of deep structural flaws probably linked to weak soils and inadequate sheet piling".

"It is important that everyone realise", said Dr Rogers, "all this is doing is putting you back to where you were before Katrina." He pointed out that adjusted data on the 29th August 2005 hurricane suggests that it barely exceeded the force of a storm the levee was designed to protect against.

Dr Rogers didn't think the restoration possible by June 1st would protect the city if there was another hurricane of this calibre.

The system in place last August was supposed to withstand a fast-moving Category 3 storm.

Now categorised as the more destructive 'slow-moving' Category 3 storm, Katrina washed away miles of earthen levees, breached canal walls and ushered in floodwaters that inundated at least 75 per cent of New Orleans.

One important piece of news for the beleaguered people of New Orleans is that emergency Federal money will be available to meet the full cost of building a new six-lane highway across Lake Pontchartrain, strong enough to withstand surges from Category 5 winds.

The westbound section of the original bridge, listed as the longest in the world, was badly damaged by the hurricane but was quickly patched up, partly with salvaged spans.

Missing ones were replaced with a system of temporary trusses.

The new bridge, estimated to cost some $630 million, will be funded from the $29 billion voted by Congress in mid-December for hurricane recovery efforts on the Gulf Coast.

Construction is expected to start later this year for completion in 2009.

The existing bridge returned to its former operating capacity on 6th January 2006, a day that marks the beginning of New Orleans' famous Carnival season which culminates in Mardi Gras.

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