At a location in Mississippi, water from the Mississippi River, left, stands at 95.7 feet above sea level. A rise in sea level is one reason that researchers are concerned about the Mississippi River Delta.
(Katie Carter/The Vicksburg Evening Post/AP)Photos (1 of 1)
Will much of New Orleans be underwater by 2100?
Sea-level rise and sinking land mean the Mississippi River Delta's habitable land will shrink, a new study finds.
By Peter N. Spotts | Staff writer/ June 30, 2009 edition
Unless enormous amounts of soil are dumped onto the Mississippi River Delta, the region could lose up to 5,212 square miles of land to ocean and tidal marsh by 2100 – a result of sea-level rise and the land sinking.
Even if levees are intentionally breached to supply fresh sediment to the delta, the Mississippi River would fall billions of tons short of delivering enough silt to maintain a delta that looks anything like it does today.
That’s the picture two scientists with Louisiana State University have painted after trying to get a better handle on the restoration challenges facing the state’s delta region.
“This was an attempt to give real boundary conditions for restoration efforts,” says Harry Roberts, a scientist with Louisiana State University’s Coastal Studies Institute in Baton Rouge and one of the researchers conducting the study.
The boundary conditions appear unforgiving. For instance, all that remains of New Orleans would probably be the French Quarter and the airport. Lake Pontchartrain would lie beneath a vast bay. Along its southernmost reaches, the Mississippi River would remain a river only by virtue of the levees raised to contain it.
The researchers acknowledge that the study is a first cut at putting numbers to the problem. Others are likely to devise more precise estimates. “But even if we’re off by 50 percent, it’s still bad,” says Michael Blum, Dr. Roberts’s colleague on the work.
During the past 12,000 years, according to the study, up to 3.5 trillion tons of sediment have been deposited into a valley stretching from Memphis, Tenn., to the Gulf of Mexico. Some 80 percent of that muck makes up the delta plain.
On average, the river delivered 400 million to 500 million tons of sediment a year, the study says.
Now, however, some 8,000 dams stretch across the river and its tributaries in a drainage basin that covers 1.8 million square miles and flirts with southern Canada. Over the past 30 years, the two scientists calculate, the average amount of sediment that the river carries a year has been half the pre-dam amount.
Also, two centuries of levee building have sent sediment that once maintained the delta directly into the Gulf of Mexico.
This has led to substantial subsidence (or the sinking of land) in the region. Subsidence also happened as people drained the land for development, allowing the soil to dry out and compact.
Meanwhile, sea-level rise has accelerated. For much of the past 7,000 years, sea levels have risen at rates of less than 1 millimeter a year. But during the 20th century, the rate averaged 1.7 millimeters a year. And since 1993, the rate has increased to some 3 millimeters a year, attributed to the effects of global warming.
Wetlands scientists have known about these processes for years. Still, the results, which appear in the current issue of Nature Geoscience, are valuable, says Donald Boesch, president of the University of Maryland’s Center for Environmental Science. “This pulls it all together,” he says.
And the implications for restoration are profound. Deltas retain soils best when the influx pours out over regions already above sea level. That implies breaching levees above, rather than below, New Orleans. But that also puts a sizable chunk of the region’s population in the way of flooding.
In the end, the study also implies that in many areas, current restoration plans represent at best an early start on a rear-guard action that buys time for an orderly retreat from many of the region’s current coastal areas.
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Comments
2. Ted | 07.01.09
After the next hurricane decimates New Orleans, we need to draw the line. If the people of that city or the state of Louisiana wish to rebuilt on the same site, I say let them. But not one dime of Federal money should be used to rebuild on a doomed location. Yes, I know there is much history and culture associated with the old site. But nature will have it way. Federal money should be used only to buy out and relocate those we have encouraged to stay below sea level with bad public policies.
3. Bill Woods | 07.01.09
Higher sea levels are caused by agricultural irrigation and not global warming. See the article below.
Real science is in agreement that global warming is caused mostly by water vapor and to a much lesser extent by carbon dioxide. Only political science still claims that carbon dioxide is the determinant factor.
Rising sea levels are also caused mostly by water. Many areas of the world have drilled wells in reservoirs where water has been for hundreds of years. The many billions of gallons pumped out have lowered the level of these reservoirs. This water is used mostly for agriculture. It quickly evaporates, and within a month or so ends up in the oceans, raising their levels.
All agricultural irrigation water, even if it comes from rivers, is the major cause of global warming. The many millions of irrigated acres greatly increase worldwide evaporation, increasing the greenhouse effect. Even though this water eventually precipitates out of the air, it is constantly being replaced by man-made irrigation. The result is a permanent increase over “normal levels” of water vapor in the air and a hotter climate on the earth.
The percent of water vapor in the air varies from fractional to over four percent. It averages about two and a half percent, which in scientific terms is written as 25,000 parts per million. Compare this number with the 360 parts per million of carbon dioxide in the air, and you can easily see that there is no comparison. Basic theory, observations and climate models all show that an increase in water vapor of around 3 to 4% will cause one degree Fahrenheit warming of the lower atmosphere.
Clouds should also be included in the water vapor numbers. Clouds cause much of the green house effect, and the higher the water vapor level, the more clouds. In fact, when you add the effect of both the water vapor and the clouds, the combination causes about 95 percent of the earth’s greenhouse effect. The remaining 5 percent is due to carbon dioxide, methane, ozone, nitrous oxide and CFCs.
So what is this “Cap and Trade” nonsense that the political scientists are pushing. It is really a tax on everyone that ends up in the pockets of politicians as bribes, pork barrel and just plain corruption.
CO2 accounts for only 4% of global warming, and the human CO2 contribution is less than 5% of that. So the human contribution is an insignificant total of .002%. “Cap and Trade” won’t do anything to improve the environment. It is just another corrupt grab for power and money at the expense of ordinary people.
4. Varg | 07.02.09
Ted,
What do you suppose will be done with shipping and drainage in the Mississippi River after nature has it’s way? Perhaps you have a better way to spend Federal funds rather than the protection of U.S. peoples, cultures and interests? Will you pay higher cost for oils, natural gas, produce, rubber, coffee after the port of South Louisiana is shut down? Would you be willing to do this after paying taxes to evacuate the entire region of 2 million people? Are you happy with the modern American ideal of running away from problems rather than challenging them?
The Dutch have led the way in flood protection. It can be done. Sadly, it won’t, because the people of South Louisiana, who facilitate drainage out of the watershed from New York to Indiana while also importing goods up through that same region don’t have the support of those who benefit from it.
We could have built 20 complete Category 5 levee systems for New Orleans with the bailout money.
5. Mark Folse | 07.02.09
Why the obsession with New Orleans? Why not discuss where we wil relocate Manhattan?
6. Oliver | 07.02.09
What this story illuminates is the tenuous nature of our current civilization. The condition in New Orleans is but one of thousands of examples world-wide of cities on the brink of crisis: too much water, not enough water, etc. Because most of us live in large cities and don’t produce our own food, we no longer notice the vast environmental changes that are happening around us, both locally and globally. The carrying capacity of the Earth to support the current human population has been made possible by the vast influx of fossil fuel energy. However, this has not been without serious consequences, of which climate change is one of many. Our dependence on fossil fuels, mega-cities and they delicate support system is unraveling. It is only a matter of time before exceptionally large environmental and associated social upheavals will challenge our modern way of living.
7. chris | 07.04.09
In about 100 years, we could have a situation where we have run out of accessible oil, and at the same time, the worst aspects of climate change are bearing down on the human population. In that scenario, civilization and all gods whose faces we have been painting with happy faces and who we have been manipulating like ventriloquists, telling us ‘everything you humans do to use natural resources just the way you want is wonderful with me’ will EVAPORATE. No more christianity. No more muslims. No more zen buddhists. I’m glad I’m 52 years old, I won’t see it. It won’t be a nice time. By the way, billions of people might die around that time, too.
8. Nikola | 07.06.09
My advice to the people of New Orleans (and Manhattan/Long Island, where I live) is to buy or build a boat. In other words, adapt. Holding back the sea is a fool’s exercise, unless you are willing to put real money into it, like the Dutch have. But as a society, we have already decided that our money goes to the wealthiest 1%. So, plan on moving inland or afloat in the future.
10. Charles | 07.07.09
Interesting article, but like everything else, the devil is in the details.
1) The Mississippi and Atchafalyaya probably do carry only half of their sediment load now compared with historical periods but only 1 or 2% of the current sediment load is being used for rebuilding. There is obvious room to use sediment even if the load is not what it was 10,000 years ago.
2)The article predicts that sea levels will rise 2.6′ to 3.9′ by 2100. This may turn out to be the case, but actual sea levels have risen an average of 1.2mm / per year over the last 132 years equating to a little less than 6 inches during that period. As a further note, in the Middle Ages around 12th century there was a warm period where the sea level was approximately 20 cm higher than today (obviously pre-industrial age and without hydrocarbons, etc.) and in the 18th century there was the ‘little ice age’, where the sea level was approximately 25 cm lower than it is today. We understand the range of possibilites of sea level rise - just not will actually happen.
3)The rise in sea levels are assumed because of Global Warming. The famed “hockey stick graph” has been debunked and most sources report flat to global cooling over the last 10 years. Most scientist agree the globe will warm or cool - it will not remain the same. PetitionProject.org gives a list of scientist who do not believe global warming is man made as well as peer reviewed sources.
4) As an individual who is very familiar with Louisiana coastal marshes, too much weight is place on the impact of rebuilding via sediment and not enough weight to the effect of fresh water flushing out these areas. I know of hardwood bottomlands that have been killed off by saltwater intrusion alone. All they need is fresh water to regenerate - and if they do not get it, it will revert to open lakes. With regular fresh water flushing, some of these would rebuild on their own with no sediment as plants would restablilze the area, help resist storms, and encourge entrapment of whatever sediments are available.
5) The biggest barriers to actually doing something positive are politicians who have their own agendas. It’s too bad the scientist can move foward and do what is necessary even if it is small projects at a time.
11. unknown | 10.05.09
we should have a new law saying every one should recycle if not a one thousand dollar fee. And the fees should be used to help us with more green products please help your next generations to come an experiance the goods you got from morther earth ! can fix this promblem if we work together an if we dont nuthing will be here so please stop pointing the finger an lets get cracking!
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1. Jay Tillotson | 07.01.09
It has been years since I read the book but I think that John McPhee in his book “The Control of Nature ” writes about the unintended consequences of man’s interference on trying to control the Mississippi River. For some odd reason I believe I read that book at the same time I read Paul Kennedy’s book and “The Rise and Fall of the Great Powers” and no one seems to consider that relevant to our national and international situation today. In both cases I think that these writers asked people not to be so sure of their certitudes.
Jay Tillotson
Buffalo, New York