The US Army Corps of Engineers (USACE) has used metal sheets and sandbags weighing 1200kg to plug the 61m gap in the 17th Street Canal, which had allowed water to spill into the city, flooding the area.

USACE efforts to dry out New Orleans have shifted now to London Avenue. Engineers are building a dike out of rocks at the head of the canal to stop the water flowing and a crane has been driving 18m long steel panels into the muddy canal bottom to block additional water from entering. About 7000 tons of stone and gravel were being dumped into one levee breach reachable via a narrow gravel road above the waters, and helicopters were dropping hundreds of 3175kg sandbags into a further breach that is still inaccessible to work crews on the ground.

The 764km New Orleans levee system was built to contain the waters of the Mississippi river and Lake Pontchartrain. It was ruptured in several places when Hurricane Katrina stuck on 29 August, and the city’s pumping system, in place to keep out floodwaters, was also damaged. The levee system was designed to deal with level 3 hurricanes; it could not cope with Hurricane Katrina, which was at least a level 4.

Electrical service has now been restored to more than 632,000 of the 1.1M customers affected by the hurricane. Limited service has been restored to the Central Business District and downtown New Orleans but close to half a million consumers are still left without power and the company has warned that the severe damage caused by Katrina will require months to rebuild.

To date, the transmission system has 54 lines and 46 substations out of service although overall restoration of the transmission system is progressing well, except in the areas impacted by flood waters or security issues.

Mayor Ray Nagin, having seen the city from air, said that about 60% was under water, compared to 80% during the worst period last week.

The Mayor estimates that it will take three weeks to remove the water and at least the same again to clear debris. Nagin has warned residents still holed up in the ruined city to evacuate, or be removed by force.

The US Environmental Protection Agency (EPA) has confirmed that the floodwaters in New Orleans are heavily polluted. The EPA has identified at least 10 times the acceptable levels of sewage-related bacteria, including potentially lethal E. Coli. Toxins like oil also infect the waters, as well as dead bodies washed up from flooded cemeteries.

It is thought that the death toll in the city could reach 10,000.

Meanwhile, President Bush intends to spend as much as US$40B to cover the next phase of relief and recovery. Estimates have placed the total bill for the clean up as north of US$150B.

The government has yet to put an official price tag on Hurricane Katrina, but it looks set to be the most expensive natural disaster in US history.