What would happen if another Hurricane Katrina hit New Orleans today?

Five years ago, Hurricane Katrina ravaged New Orleans with a 28-foot (8.5 meter) storm surge and 2 feet (61 centimeters) of rainfall. The water easily breached the city's old levee system in about 50 places and damaged half its water pumping stations. By the time the storm had passed, the majority of the Big Easy was submerged.

"The extent of damage was more than anyone could have imagined," said J.W. Sneed, deputy mayor for public safety and director of the New Orleans Office of Homeland Security & Emergency Preparedness.

Since then, government officials and scientists have sought to transform the lessons learned from that damage into better policy. But the city is still recovering, and much work remains to be done to reduce its vulnerability to future Katrina-like storms.

IN PICTURES: Hurricane Katrina 5 years later

Rebuilding natural protection

For centuries, Louisiana wetlands have acted as a natural buffer against hurricanes by slowing down storms, reducing wave size, and decreasing the energy of storm systems. According to scientists at the Louisiana State University Hurricane Center, existing wetlands reduced water speed from 7 to 3 feet per second (2 to 1 meters per second) during Katrina.

Over the last 70 years, however, an area of wetlands the size of Delaware has disappeared. After Katrina, the state recognized the danger of losing more wetlands and created the Coastal Protection and Restoration Authority. In a report last year, the agency recommended coastal restoration measures to repair some of the damage done by pipeline construction, poor urban planning and natural subsidence (sinking of land).

Today, the U.S. Army Corps of Engineers is working to implement some of these measures. They plan to divert Mississippi River freshwater, nutrients and sediment to rebuild and sustain wetlands. The region will benefit from these improvements, should a major hurricane strike in the future, according to the agency.

Engineering a new levee system

According to a 2006 investigation by engineers at the University of California at Berkeley, sections of New Orleans' levee system were incomplete and eroding when Katrina hit. The levees were almost 2 feet (61 centimeters) below their original elevations because of subsidence and unstable soils.

Moreover, a U.S. Army Corps of Engineers task force found that none of the city's pump stations were working during Hurricane Katrina. The pump stations should have drawn floodwaters from the streets into nearby lakes once the levees were breached, but they simply weren't designed to handle that volume of water.

So far, Corps engineers have increased levee height and replaced many of the old levee system's concrete I-shaped walls with T- and L-shaped walls, which consist of steel support beams that extend as far as 65 feet (19.8 meters) below sea level and will provide better support, should the levees fill to near capacity during a future storm. Pump stations are also being storm-proofed.

Hurricane Katrina also illustrated to engineers that the traditional, wind speed-based Category 1-5 system of rating hurricanes is not an accurate predictor of how a storm may affect a city. In repairing and renovating New Orleans’ 350 miles (563 kilometers) of levees and floodwalls, the task force is using a different type of hurricane modeling — based on storm size and intensity — to ensure that the new system provides protection that can stand up to 100-year storms.

When finished next year, the $14.45 billion Hurricane and Storm Damage Risk Reduction System will give New Orleans the most advanced defense against flooding in the city’s history.

Preventing complacency

The protection offered by coastal restoration and levee system improvements would be undermined without effective emergency management.

"Katrina began as a hurricane but only became a disaster because of significant, preventable planning and management failures," according to a 2006 paper from Victoria Transport Policy Institute in Canada.

The city failed to use public transportation, such as buses, to evacuate residents. Those with cars were subjected to delays of several hours on highways without the option to refuel. Communication faltered between city authorities, state officials, shelters and hospitals. Following the storm, half a million residents were displaced and many were without essential supplies.

With the passing of the 2006 Post-Katrina Emergency Management Reform Act, Congress hoped to improve communication and reduce loss of life in the event of another Katrina-like storm.

The act reorganized the Federal Emergency Management Agency (FEMA). It offered grants to help cities revise evacuation plans, included provisions for better communication with non-English speaking people and those with disabilities and recognized the evacuation needs of people with pets. The act also increased funding for Urban Search and Rescue teams and requires the establishment of a family registry within six months after a storm.

The city of New Orleans has improved resident access to evacuation and alert information. For example, they have an e-mail and text message system called NolaReady that 13,000 residents have signed up for.

Even the best plans will fail, however, if residents don't heed evacuation warnings, Sneed told Life's Little Mysteries. With Hurricane Gustav in 2008, 97 percent of residents evacuated when the mayor declared a mandatory evacuation, but with each passing year there is the risk that people will lose a sense of urgency regarding Katrina-like storms.

"Since there has not been another major storm since," Sneed said, "the chance for complacency to slip back in amongst our citizens is always a serious concern."

IN PICTURES: Hurricane Katrina 5 years later

• Infographic: Hurricane Katrina History and Numbers
• A History of Destruction: 8 Great Hurricanes
• Which US Cities Are Most Vulnerable to Hurricanes?

This article was provided by Life's Little Mysteries, a sister site to LiveScience.