Five Years Later, Could New Orleans Withstand Another Major Hurricane?

By Andrew Moseman | August 30, 2010 11:07 am

Hurricane_Katrina_FloodingThe city of New Orleans’ defenses are certainly better than they were five years ago, when Hurricane Katrina breached the levees and flooded the city. With the five-year anniversary of that disaster upon us, however, the question that hangs in the air is: Would those refurbished barriers stand up to another Katrina, or something worse?

Better Barricades

In the last five years, the federal government has invested about $15 billion to revamp the New Orleans levee system.

This time, tougher foundation material like a mixture of construction clay and cement, is being used in the soil to hold structural sections of wall designed as an inverted T instead of their previous I-shape. The new design is considered stronger, allowing steel pillars to bracket each end into the ground. Total completion is expected in June 2011. [Christian Science Monitor]

The levee system stretches about 350 miles around the city, and its walls stand about 30 feet high (Katrina’s storm surge rose to about 28 feet).

Bigger Storms?

Gregory Gunter of the U.S. Army Corps of Engineers trumpets the new systems as a defense against the so-called “100-year storm”—a tempest so bad it has only a 1 percent chance of striking in a given year.

The system shouldn’t fail in a “400-year” Katrina-strength storm either, although Gunter says such a surge would probably flow over the barriers. This would lead to some flooding, but nothing like the scale of Katrina, which pushed over walls and breached levees. [New Scientist]

However, flood experts point out, the people who really know about keeping flood waters at bay—the Dutch—build their levees with a much larger investment, intending them to withstand a “10,000-year” event. In addition, because our hurricane records go back only so far, and because the past may not be an accurate picture of future storms, those year designations may be misleading anyway.

Paul Kemp, director of the National Audubon Society’s Louisiana Coastal Initiative in Baton Rouge, and former storm surge modeller, says the new designs presume that future storms will resemble past ones. He points out that climate change may increase hurricane strength. [New Scientist]

Don’t Forget the Wetlands

The Corps of Engineers has taken its share about abuse for Katrina failures (including by New Orleans resident Harry Shearer of The Simpsons and This Is Spinal Tap fame, whose new Katrina documentary is out now). The levees weren’t the only problem, though: New Orleans’ degraded wetlands put the city in added danger.

According to the Army Corps, all of the levees that failed during Katrina lacked wetland protection; the levees with a wetland buffer remained intact. Scientists have estimated that storm surge is diminished by one foot for every square-mile of wetland it travels through [National Geographic].

Now, groups like the Sierra Club are trying to revive the cypress ecosystem that once thrived in the shallow waters, and are doing so with a plan that actually requires pumping in partially treated sewage. With a high enough volume of biosolids—semi-treated sewage—they could add up to four feet of new material in which plants could take root.

The swamp has been killed primarily through saltwater intrusion from the various surrounding canals that connect the Mississippi River to the Gulf of Mexico. A pulse of freshwater sewage could make the site more suitable for wetland species. In return, those species would help filter and clean the effluent [National Geographic].

Unknown Toll

President Obama spoke at Xavier University of Louisiana in New Orleans yesterday to mark the Katrina anniversary, praising the growth of small business and announcing that the federal government was finally ready to dole out its promised $2 billion investment in the city school system. But one thing still remains unsettled: Just how many people we lost, and who they are.

The Houston Chronicle reports that about 500 of the 1,500 people in Louisiana’s recognized death toll remain unidentified. And that official count could be a lowball figure, some argue:

John Mutter, a Columbia University professor, has been gathering personal testimonials and public records of those killed in Katrina for an effort he calls Katrinalist. Mutter estimates the true death toll will top 3,500 if those killed by the storm and by its many after-effects are accurately tallied. And yet other counts put the toll at an estimated 1,800 [Houston Chronicle].

Related Content:
DISCOVER: A Striking Visualization of Hurricane Katrina
DISCOVER: 20 Things You Didn’t Know About… Hurricanes
DISCOVER: The Next Katrina
The Intersection: New Orleans, Then And Now

Image: Office of the President of the United States

CATEGORIZED UNDER: Environment, Technology
  • http://www.freewebs.com/wetlandsmiss/ Ken

    Could New Orleans and south Louisiana flood from a future man made mistake?

    Wetlands restoration will produce an unstable or stable Mississippi River?
    http://www.freewebs.com/wetlandsmiss/

    A Yes or No needs to be the answer but I have not received an answer and the question was posed a few years ago to my elected officials.
    Ken

    …The present Master Plan for wetlands restoration only covers one side of the fence. The plan discusses 20% to 30% of the river being diverted along the Mississippi River between Donaldsonville and the mouth of the river and, I believe, this will make the river unstable. The other side of the fence is diverting with keeping the river stable and I want to share some ideas of how, I believe, to keep the river stable.

    General explanations about both sides of the fence:

    LA Speaks Draft Master Plan will not work because a river environmental disaster will occur with the plan as proposed
    Louisiana’s Comprehensive Master Plan for a Sustainable Coast

    http://www.lacpra.org/

    I worked at a chemical plant next door to the plant where the following incident happened. A shipping terminal fell in the river in the 1973 flood near Plaquemine, La. and I believe from high velocity water but I am sure the terminal was designed to meet government regulations with respect to piling depth…etc. After this event several diversions were added to the river and this has added piling undercutting capability to the river due to added velocity. Adding more diversions in the future may be the straw that breaks the back and, I believe, more shipping terminals will fall into the river. There should not be any added diversions that increases river velocities except for diversions close to the mouth of the river. Diversions close to the mouth of the river essentially do not increase river velocities and do not decrease the resistance of the river. But any diversions above the mouth of the river decrease the resistance of the river by creating a parallel run with the river. This parallel run starts at the point of the river diversion and continues downstream to the Gulf. These added diversions will decrease the downstream resistance and river velocity north of the diversion will be higher than before the diversions are added.

    “A combination for shipping terminals to fall into the river”

    I believe there is nothing that can be done to stop the added erosion power of the river from undermining shipping pilings. Also I believe, grading, armoring the river bank with stone, and installing concrete matt on the river bank will not stop the erosive power of the river, from higher velocities, undermining the levee at peak meander points. And this undermining of the levee will send a destructive tidal wave into Southeast Louisiana.

    The Mississippi River Master Plan diversions will only work if:

    All future diversions are close to the mouth of the Mississippi River.
    Or the total flow of the bird foot delta area is decreased by the added upstream diversion flows.
    A magnitude example of possible diversions

    Third Delta Conveyance Channel General Pathway

    http://www.restoreorretreat.org/solution_third_delta_conveyance.php

    The Third Delta Conveyance Channel diverts about 1/3 of the Mississippi river and will be located below Donaldsonville La. and may well destroy Southeast Louisiana because the levee above Donaldsonville, Louisiana will be undermined. Higher river velocities above Donaldsonville will be generated by the Conveyance Channel flow because the flow will decrease the river resistance below Donaldsonville. These higher velocities will undermine peak meander points of the river above Donaldsonville and in turn the levee will be undermined and collapse sending a tidal wave south.

    Please see below article that shows stream channelization increase flow velocity.

    I believe one can safely conclude:
    • Stream channelization reduces the resistance of a stream and this is why the stream has faster velocities.
    • For the Mississippi River, approximate 1/3 of the river diverted by the Third Delta Conveyance channel will reduce the resistance of the river and as a result the velocity and the erosive power of the river upstream of the diversion will increase.

    ***********************************

    …Because overall stream behavior is maintained in dynamic equilibrium, changes in one of several variables such as flow, velocity, or streambed substrate will result in compensating changes in the other variables. Channelization and armoring (rip-rapping) of a stream section will cause permanent changes, removing the dynamic nature of not only the altered section, but also affecting the adjoining stream sections further downstream than might initially be anticipated. Stream channelization often increases stream velocity, thereby increasing the erosive power of the stream. Durable protection or armoring is then required to ensure the stability of the engineered modification through all flow events….

    http://www.fws.gov/midwest/KalamazooNRDA/documents/IChap_8.pdf

    Page 5

    ********************************

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