When it comes to hurricane evacuation, city and state emergency managers have always stressed there is no room for the “better late than never” mentality. Those who wait, they say, may never get out.

Now a team of engineers has assessed the city’s hurricane protection system and come up with hard evidence to back up that claim — a timely warning, what with the June 1 onset of hurricane season just days away.

The team, engaged by the Lake Pontchartrain Basin Foundation, finds that sections of Interstate 10 on the city’s primary eastern and western evacuation routes will flood long before storm surge threatens levees and floodwalls because they are at ground level unprotected by storm barriers.

Chris Guilbeaux, a deputy director of the Governor’s Office of Homeland Security and Emergency Preparedness, said those weak links are well known and have been factored into the state’s timing of evacuation calls — and its insistence in urging residents not to delay.

“We evacuate before a storm, not during one, which is why evacuation plans are set for 50, 40 and 30 hours before tropical storm conditions [winds of 40 mph] are expected at the mouth of the river,” he said.

“We know those areas will flood because that’s just what happened during Hurricane Isaac,” he said.

One section is a 1.7-mile stretch of I-10 that runs between the hurricane protection levees near Irish Bayou and the elevated Twin Spans that cross Lake Pontchartrain just to the east. The highest elevation of this problem area is about 7 feet.

The other section is a 3.8-mile stretch on the north side of LaPlace between elevated sections of I-10. Its highest elevation is 2 to 3 feet.

The surge from even small hurricanes can top those heights as Category 1 Isaac proved in 2012. That slow-moving storm stalled over the area, allowing the surge to build up on the western reaches of the Pontchartrain basin, eventually flooding I-10 and spilling into homes in LaPlace.

Guilbeaux said the state would like to have those exposed sections of I-10 either raised or protected by levees, but lacks the funds. Even then, evacuation orders would still be issued long before a surge would flood them.

“You don’t get a 7 or 8 foot surge with a 40 miles per hour wind, which is when we issue those orders,” he said. “As always, the best way to avoid trouble is to be prepared, and leave when the order goes out.”

The engineering team said providing protection for those sections could help an additional 5,000 vehicles clear the city.

The team was evaluating how the city’s defenses conform to a “systems engineering” approach, which requires that each link in a system work toward the same goal. In this case the goal is reducing the risk of harm to residents from surge. The low-lying section of a major evacuation route failed that test.

Bob Marshall

From 2013 to 2017, Bob Marshall covered environmental issues for The Lens, with a special focus on coastal restoration and wetlands. While at The Times-Picayune, his work chronicling the people, stories...