Atmosphere And Weather

Why the Mississippi River Delta Basin is in serious Trouble

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"Why the Mississippi River Delta Basin is in serious Trouble"
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Four inches of rain are predicted this week in early spring, raising alarm among some that the Mississippi River will rise to dangerous levels. Civil engineers say the levees will hold, but residents remain alarmed. Time to take a broader look at weather patterns that have devastated this region of the US.

Katrina hits Florida as a Category 1 Hurricane. Then as it entered the warm waters of the Gulf it picked up steam, increasing to approximately a category 4, and took her wrath out on New Orleans. She flooded coastal lands from Alabama all the way to Florida. Among thousands of people killed and over 700 missing, it left the coast with 900,000 homes without electricity. Why was this coast hit so hard with flooding?

One indication of hurricanes on the rise and more powerful storms exist with the rising global temperatures. A more predominant warm surface stream current comes right up the Atlantic Coast. This current is a great street for hurricanes to pick up steam. Along with rising sea levels, due to mountain glacier melting, combine an avenue that crashes into the Gulf Coast and Mississippi River Delta Basin. La Nina is on the rise in 2007 and Louisiana may not have seen the end of it yet!

La Nina takes place when the waters off the northwest coast of South America when the Pacific Ocean becomes cooler then usual. This allows the vertical shear to become low along the surface pressure of the Atlantic thus allowing hurricanes to easily form in the Atlantic Ocean. In El Nino the waters of the Pacific become extremely warm and cause low vertical shear in the Pacific. This would create more hurricanes in the Pacific Ocean.

During an La Nina there is approx. a 70% chance of having 2 or more hurricanes in the Atlantic and we are in a projected La Nina right now. The Gulf coast is part of what I call, "soaking and cutting." When an El Nino is present the coast from Florida to Texas receives above average rainfall this is what I mean by soaking. And when a La Nina is present there is a storm strip that heads right up the Mississippi River Delta this is what I refer to as cutting.

With subsidence taking place and sea rise New Orleans is in a world of trouble! It is estimated at the present state of the coast by the Handley Computer Model that by the year 2100 The east Coast and Gulf area will have suffered land loss of massive capacity and many of our great cities in the U.S. will be lost.

One problem is that the Louisiana Coast is losing land mass 3 times faster than ever recorded in it's history. Why? One reason is in the more northern areas of the Mississippi River Basin there are so many dams and man made canals that the amounts of sediments and nutrients just do not reach the delta area anymore. These sediments over the last 6000 years produced approx. 9600 sq. miles of land and in the last 70 years the Gull Coastal area has lost 1900 sq. miles. In the delta area the problem is amplified by poor engineering of levees and canals.

In 1963 the army corps of engineers completed, (ORCS), Old River Control Structure. This was a successful attempt to not allow the Mississippi River to Flow down the Atchafalaya River. For the good of the City and the vast oil industry in the Gulf they wanted to keep the river flowing through New Orleans. The problem is the river has since become so flat to sea level it doesn't have any down slope to carry sediments needed for land building. Not only has the river flattened but ship cannels in the New Orleans area actually amplified the storm surge. This is one of the biggest problems facing the New Orleans area right now!

New Orleans sits below sea level in between the Mississippi River, south, and Lake Ponchartrain to the north. The, (MRGO), Mississippi River Gulf Outlet, a man made canal, sits just below Lake Borgne and runs right towards the city of New Orleans and saves ship traffic up to 40 hours of travel time. This canal merges with GIWW, an Industrial canal between Lake Ponchartrain and Lake Borgne. This actually created a funnel that the storm surge and rising sea level surge could come straight into the city of New Orleans.

The initial surge rose well above the 23' height of the levee walls. Lake Borgne Surge over 40' and tried to come up the MRGO and the GIWW into a funneled area that lead into one solitary Industrial canal, this is where a serious breach takes place. MRGO was breached in over 20 places. Some levee walls moved as much as 45'. Lake Borgne was at elevations at least 10' higher then Lake Ponchartrain, the water moved seeking sea level into Lake Ponchartrain and New Orleans. Lake Ponchartrain the sent water up the 17th Street Canal and the London Canal breaching there levees and filling Northeast New Orleans with devastating flood waters.
he continued rain and streets took the water easily through the streets of New Orleans, which was already under normal sea level, flooding 80% of the city in critical conditions.

Problems with the levees were that some were just poorly built, with loose soils around there perimeters. When setting a wall on top of a levee there is no pill over to create any amount of natural levee. So as time went on the sediments in these manmade canals was removed and carried out off the coastal shelf by natural erosion. When the waters surged some of the levees actually were breached from the bottom up. Others gave way when the spill over ate away levee soil along the break walls and the breached underneath from removed soils weakening the structures. Another problem of subsidence was the removal of wetland marshes and woodlands to build the canals.

Wetland and wooded marshes act as storm buffers for the coastal area by removing these for ship movement they created a direct access for storms to New Orleans. A levee system in nearby 20-Arpent Canal actually stands undamaged and this was probably due to the fact that this canal was protected by Marsh and wooded wetlands. It is estimated that just 300' of wooded wetland to the south of MRGO and East of New Orleans wood have cut the surge down by 90%. Although some scientist would argue that there is just not enough time left to save the Louisiana Coast.

It took 6000 years to build 9600 sq. miles of land and we don't have 6000 years to fix the problem. Global warming and rising sea level with subsidence surely means the coast has more problems then the Mississippi River. The levee walls actually sunk over 3 inches since they were installed at MRGO. The continental pressure is pushing the coastal loose soil right into the ocean. The Gulf Coastal shelf falls fast and can devour loose sediments. Since there are over 50,000 oil refinery related businesses in the Costal area the mining of oil has left low pressure areas under the surface soil that can easily be invaded by salt waters, making the entire coast a floating kind of mush ready to give way to erosion.

In conclusion, New Orleans best bet might be to move up near Baton Rouge and letting the delta return to it's more natural state. I also encourage the planting of Coastal trees and plants but at this point the salt water intrusions are definitely a problem to the required nutrients to up hold a healthy coastal environment. If you don't live in New Orleans I wouldn't suggest relocating there any time soon!

More about this author: Mark Pavuk

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