A Pressure-Filled Repair Job

The Army Corps of Engineers increased the rate that floodwaters in New Orleans were being pumped out Tuesday, but the agency was still taking a slow approach out of concern that hidden damage could cause new breaches in storm walls and levees.

The tremendous power of Hurricane Katrina, which tore hundreds of feet of steel-reinforced storm walls in three drainage canals, has left engineers worried that other sections of the complex flood-control system are weakened and could fail without warning, said Col. Richard Wagenaar, the corps’ district engineer for New Orleans.

“The last thing we want is another flood wall to go down,” said George Stringham, a spokesman for the corps. “We are not 100% certain of their strength. We are going to move carefully to see how much pressure they can handle.”

As the water levels drop on the city side of the storm walls, they will be subjected to millions of tons of pressure from the higher waters of Lake Pontchartrain. Engineers are worried that Katrina might have undermined wall foundations, which are hidden in many sectors because of flooding.

The agency began pumping operations late Monday, running a single temporary pump at about 100 cubic feet per second, a “drop in the bucket” in terms of the volume needed to reclaim flooded sections of the city, corps spokesman John Hall said.

By late Tuesday, officials had increased the pumping rate to 2,000 cubic feet per second, an encouraging improvement but still far short of the massive volume required.

The permanent pumps at the 17th Street Canal are capable of moving 9,380 cubic feet per second, roughly the flow of the Colorado River below Hoover Dam. Those pumps were inundated and their electric motors must be “baked dry,” a process that could take a couple of weeks, Wagenaar said.

New Orleans flooded Aug. 29, when Katrina caused an approximate 12- to 13-foot surge in the water levels of Lake Pontchartrain. A counterclockwise wind of 135 mph roiled the lake and pushed water over the top of storm walls that protect the city.

After a still-unknown period of time, the churning waters, pounding surf and scouring action at the foundations caused the walls to collapse in three areas, inundating parts of the city.

The corps has completed temporary repairs to the breach of the 17th Street Canal. Two breaches of the London Street Canal have been mostly plugged, though the corps continues to build its temporary wall higher and wider. It is still evaluating the strength of the repairs. The third site, Industrial Canal, has two breaches. The corps has started repairs to the first gap and plans to begin repairs to the second today.

Removing all of the floodwaters will require most, if not all, of the 22 pumping stations that normally operate in this city, much of which is below sea level. Those pumps are operated by the Orleans Sewer and Water Board, not the Army Corps of Engineers.

In some sections of St. Bernard Parish, the water remains 30 feet deep, the corps said.

The city is divided by levees, storm walls, canals and other features -- a system so complex that corps officials were at a loss to describe exactly how pumping out one section would affect others.

Getting the permanent pumps operating also involves many unknowns. The pumps might very well be clogged with debris, mud, even corpses.

Engineers in New Orleans are under growing pressure from officials in Washington who want the water pumped out as soon possible. The corps initially estimated that it would take three to six months to rid the city of water, but top officials in Washington scaled back the estimate to 80 days or less.

But some experts warn that the 80-day mark and even shorter estimates given by city officials do not include the task of drying out every section of the city. Ultimately, the job will take longer than many political leaders would like.

What’s more, the corps is clearly worried that if it moves too quickly, it would risk another breach that would flood the city again.

“We have a lot to save here,” said Hall, who lost his home. “We are very concerned about potential damage. We have to pump a little and see if we are causing problems.”

Indeed, large portions of New Orleans are not below water and need to be protected, Hall said. Sections of the city south of the Mississippi River, known locally as the West Bank, were largely spared of flooding.

Much of the city that hugs the meandering river lies on high ground, because over centuries the river deposited sediment that raised the banks above the nearby lowlands. Jefferson Parish to the west has spot flooding from heavy rain but was not inundated by Lake Pontchartrain, Hall said.

The Environmental Protection Agency has given the corps clearance to begin pumping operations. The EPA granted a waiver allowing the corps to pump contaminated water into Lake Pontchartrain, which could damage the lake and the estuaries in the Gulf of Mexico.

EPA officials are conducting water surveys to characterize the pollution in the floodwaters. Hall said the most serious contaminates might be petroleum products, which float on the top, meaning that the initial pumping will remove relatively cleaner subsurface water. Experts are looking at ways to mitigate problems when the most polluted water is pumped in coming weeks or months.