The vulnerability of stricken New Orleans was starkly highlighted Sept. 19 as a new hurricane erupted in the tropics and spun into the Gulf of Mexico. Engineers and contractors who were on the verge of declaring victory in their mission to drain the flood left from Hurricane Katrina’s levee-busting rampage suddenly found themselves shifting to demobilization and evacuation planning and around-the-clock breach and scour repair.

The new storm threat made it painfully clear that any hurricane crossing the Gulf of Mexico in the wake of Katrina could have serious consequences for New Orleans’ crippled defenses, even if it makes landfall far away. On Sept. 20, Hurricane Rita was projected to make landfall west of New Orleans, in southwest Louisiana or Texas. But New Orleans likely would still have to deal with rain from the storm’s eastern fringe.

Surge Protection. Gates would shut canal. (Photo by Tom Sawyer for ENR)

Even modest winds, rain and seas from the fringes of a storm could result in large-scale flooding of portions of the city, says Col. Duane Gapinski, district engineer from the U.S. Army Corps of Engineers’ Rock Island, Ill., district, who was tapped to lead the unwatering mission in New Orleans. That possibility sent the Corps scrambling to shift the focus from getting the last of Katrina’s water out of the city, to making a detailed pump-by-pump and basin-by-basin evaluation of the drainage system’s remaining capacity, repair prospects and stopgap alternatives.

Measures included shifting portable pump capacity and filling and pre-positioning 800 7,000-lb sandbags for helicopter drop in the event of new breaches, with another 2,500 more to come. The goal is to devise a strategy to manage a heavy rain event, or a new overwash and seawater inundation.

"Well, we know how to do it now," says Gapinski, whose mission is expanding, at least for now, into ongoing pump and levee repair. He reorganized his team on the night of Sept. 19 to beef up storm defenses as Hurricane Rita appeared poised to enter the Gulf of Mexico and possibly threaten Louisiana. "We will have unwatered the City of New Orleans in 21 days once…now we may have to do it all over again" he says.

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Task Force Unwatering segued without pause into Task Force Guardian, a levee restoration program supported by the Corps’ district office in St. Louis. That district, like several others, is aiding the victim district in New Orleans. In light of the Rita threat, New Orleans District Engineer Col. Richard Wagenaar abruptly postponed plans to reconstitute his staff, scattered by the evacuation and devastation of Katrina, until the threat of another flood abates.

"It doesn’t take a major storm. It does not even take a tropical storm. That’s the kicker," says Col. James Rowen, commander of the Corps engineering research and development center at Vicksburg, Miss. Computer models developed at the center show that, even without a storm surge, the city would experience serious re-flooding from a relatively modest 3-in., 6-in. or 9-in. storm event in a six-hour period at remaining drainage capacities.

Constraints

Before the hurricane, the city’s system could be counted on to handle 1 in. of rainfall in the first hour and ¹/₂in. of rain in subsequent hours without ponding. The Corps reports about half of the city’s installed pumps are mechanically operational. But there are many constraints on full operation, including limitations on power supply and the probable need to shut some down in the event of another storm-surge from Lake Pontchartrain. Under every scenario, some combination of restraints will keep the operation from hitting theoretical maximum.

There also is an additional 1,470 cfs capacity in the 24-in., 30-in. and 42-in. portable pumps scattered on localized drainage issues across the city, although that capacity is a pittance compared to the installed system. The Corps began redeploying the portable pumps for more strategic storm water management support Sept. 19.

Maj. George Stejic one of the managers of the Corps’ unwatering team, reported on Sept. 19 that pumping capacity, with installed and supplemental support, to empty the main city portion of Orleans Parish was at about 34% of the original rate of 38,735 cfs; East Orleans at 90% of original 4,600 cfs and St. Bernard Parish at about 80% of the original 6,311 cfs. Capacity for pumping the east bank of Plaquemines Parish stood at 86% of 3,039 cfs, and the west bank at 80% of the original 9,043 cfs. Click here to view chart

Work to restore the city’s main pumps is progressing, but it simply requires time, says C. Joseph Sullivan, the general superintendent of the New Orleans Sewerage & Water Board. He says the city has 21 pump stations, most of which have multiple pumps. Many of the electric motors that drive them were at least partially submerged in the flood. The windings on each motor must be thoroughly dried before re-energizing, a process that can take about two weeks with the biggest motors.

General Electric Co. has a contract with the Sewerage & Water Board to put a team on every pump for the drying out process, although the Corps is chaffing at GE’s rate of mobilization. The drying technique also was changed after one of the tarp blankets trapping heat on a pump at Pump Station No. 6 caught fire. Crews switched to charging the windings with power from generators to heat them up and drive out the moisture.

Stephen Cason, GE senior sales associate in charge of the pump project, says his firm has been on the pump project since Sept. 2 and now has 40 people working. GE also is working with local Walter J. Barnes Electric Co. Inc.

"Our only limitation for manpower is the Corps’ ability to clean and sanitize worksites," Cason says. GE officially received the purchase order from...