Hurricane Isaac Surprises With Flooding and Storm Surge

Hurricane Isaac isn't the strongest hurricane to hit the Gulf Coast or near New Orleans, but it's creating havoc because the storm is moving so slowly. The winds aren't the problem with the storm, it's the flooding rains and accompanying storm surge while the storm is progressing at a crawl.

The storm surge is higher than models had predicted yesterday. As Jeff Masters notes:

Isaac is bringing large and dangerous storm surge to the coast from Central Louisiana to the Panhandle of Florida. At 10 pm EDT, here were some of the storm surge values being recorded at NOAA tide gauges:

6.2' Waveland, MS
9.9' Shell Beach, LA
3.0' Pensacola, FL
4.4' Pascagoula, MS
3.4' Mobile, AL

The 9.9' storm surge at Shell Beach, which is in Lake Borgne 20 miles southeast of New Orleans, exceeds the 9.5' surge recorded there during Category 2 Hurricane Gustav of 2008. Research scientists running a Doppler on Wheels radar located on top of the 16' levees in Plaquemines Parish near Port Sulphur, LA, reported at 8:30 pm EDT that a storm surge of 14' moved up the Mississippi River, and was just 2' below the levees. Waves on top of the surge were cresting over the west side of the levee. Needless to say, they were very nervous. Over the past hour, the surge has retreated some, and waves were no longer lapping over the top of the levee. This is probably due to the fact that we're headed towards low tide. A storm surge of 9.5' has moved up the Mississippi River to the Carrrollton gauge in New Orleans. This is not a concern for the levees in New Orleans, since the storm surge has now brought the river up to 2.5' above its normal water level, which was 7' low due to the 2012 U.S. drought. The highest rise of the water above ground level will occur Wednesday morning over much of Southeast Louisiana, Mississippi, Alabama, and the western Florida Panhandle, when the tide comes back in. It is clear now that this storm surge event will be as dangerous as that of Category 2 Hurricane Gustav of 2008.

Plaquemines Parish is reporting that levees in the area have been overtopped by the storm surge and caused significant flooding. The levees involved aren't part of the network of levees upgraded or built to protect New Orleans following Hurricane Katrina.

The parish levees on the east bank are about 8.5 feet high, and some estimates have storm surge at 13 feet. At daylight, the National Guard is expected to launch a larger rescue effort, coming into the east bank through St. Bernard. After the wind subsides, other water and air rescue efforts likely will launch.

While federal levees in the area appear to be holding, problems in Plaquemines Parish are occurring in areas not protected by the federal system, which was revamped after Katrina.

Guy Laigast, director of the parish's emergency preparedness, says that an 18-mile stretch of the parish east bank back levees might be overtopped from Braithwaite to White Ditch and that some points might be seeing 110 miles per hour winds. There are many varying reports of wind speeds, generally ranging between 80 and 110 miles per hour.

"The devastation of my house is worse than Katrina and the flooding in Woodlawn is worse than Katrina, so those things tell me that the damage on the east bank is worse than Katrina," Plaquemines Parish President Billy Nungesser said this morning.

So far, the New Orleans flood control systems are doing their job and protecting the city from the Mississippi River, the flooding rains, but this storm is going to take a long time before moving away from the region.

Law enforcement has been working to rescue those caught in the flood waters, but private citizens are also busy helping out their neighbors and others stranded by the flooding. One father-son team has already rescued 23 from the rising waters. Parts of the Gulf Coast could see up to 20 inches of rain with 7 to 14 inches falling over a widespread area.

The storm has left hundreds of thousands without power across the Gulf Coast,

Drought Continuing to Cause Major Disruptions on Mississippi River

The ongoing drought, which is one of the most severe in the last 100 years, is causing significant problems up and down the Mississippi River. The river's watershed is heavily affected by the drought, which has caused water levels to fall to close to historic lows. That means that boat traffic has slowed down, costs have gone up, and perhaps most dangerously, the salty waters from the Gulf of Mexico are pushing up the river towards New Orleans.

The Army Corps of Engineers is doing what it can to stave off a complete shutdown of river traffic and protecting the New Orleans water supply. They're busy dredging stretches of the river to keep it passable, and they're building a sill below New Orleans to try and keep the salt water from flowing up the river. Normally, the Mississippi's water flows are sufficient to keep the heavier salt water from coming upstream, but the drought conditions have lowered the flow rates.

The Army Corps of Engineers has more than a dozen dredging vessels working the Mississippi this summer. Despite being fed by water flowing in from more than 40 percent of the United States, the river is feeling the ruinous drought affecting so much of the Midwest. Some stretches are nearing the record low-water levels experienced in 1988, when river traffic was suspended in several spots.

That is unlikely this year, because of careful engineering work to keep the largest inland marine system in the world passable. But tow operators are dealing with the shallower channel by hauling fewer barges, loading them lighter and running them more slowly, raising their costs. Since May, about 60 vessels have run aground in the lower Mississippi.

The low water is not just affecting the 500 million tons of cargo like coal, grain and fertilizer that move up and down the river each year. The owners of the American Queen, a paddle-wheel steamboat that takes passengers on tours along the inland waterways, decided not to send the boat below Memphis on a trip to Vicksburg, Miss., this month. The water was deep enough, said Tim Rubacky, a company spokesman, but after conferring with the corps and the Coast Guard, the company decided that the likelihood of a barge accident and ensuing traffic closures would be too great.

“It’s kind of like a truckful of watermelons spilling over on the expressway,” Mr. Rubacky said. “Everything’s going to come to a halt.” The boat tied up at Memphis and sent the passengers on to Vicksburg by bus, he said.

The volume of water coming down the river is so much lower than normal this summer that a wedge of salt water is creeping up the Mississippi toward New Orleans, imperiling local water supplies drawn from the river. The corps is building a sill — basically, a dam of sediment — in the river below New Orleans low enough to block the flow of salt water while letting boats pass.

When the Mississippi is low, the flow slows and sediment settles, causing the river to silt up and obstructions to form, said James T. Pogue, a spokesman for the corps in Memphis. Since 1988, when record low water on the Mississippi caused navigation to shut down, the corps has engineered ways “to help the river keep itself open,” he said, building new features like dikes that stick out into the river and “sort of act like nozzles to speed up the flow of the river” to scour the bed.

Such river training structures help to reduce the amount of dredging necessary by making the river do much of the work. The result, he said, is that even if water reaches the levels that it did before, “we’ll still be in better shape than we were in ’88.”

The river’s problems are the main topic aboard the Motor Vessel Mississippi, a giant towboat fitted by the corps with meeting rooms and used during its annual low-water inspection trip, which included a public hearing in Alton, Ill., on Friday. Some of the speakers complained about the corps’ management of the river during last year’s floods, when water at Vicksburg was nearly 59 feet higher than it has been during this year’s drought. That is the nature of the river — an engineered system, managed but hardly controlled.