The coastal wetlands provide a buffer between the city and the sea. A couple of
miles of wetlands can knock a foot off a storm surge. Some call the
wetlands "horizontal levees." For three hundred years the
wetlands have been protecting the city. In the past fifty years much of
the protection has been erased. Katrina was the first hint that
there are consequences.
The map shows the wetlands loss around New
Orleans from 1932-2005 (red) and projected loss to 2050 (yellow).
Katrina accelerated the land loss. According to USGS, in the area east
of the Mississippi River 72.9 square miles of land became water in
2005. This exceeded the projection of 60 square miles loss in this area
for the entire 50 year time period. Nearly 50 square miles more were lost
in other parts of the state including 17 square miles each in the
Barataria and Terrebonne basins. Compare the total 118 square mile loss
in 2005 to 25 square miles in a more typical year.
Flash update Oct 2006 the USGS has revised the land loss estimate for Katrina and Rita upward to 217 square miles apparently the original figure only included the land loss east of the Atchafalaya.
Check
it out for yourself by clicking the satellite view. The blue stuff is
not land.
And be sure to read the
USGS Land Loss Report youself for additional details.
See the image of
Katrina loss in the Breton Sound area alone. If you have Google Earth
intalled on your computer be sure to zoom in on the Mississippi River
delta south of New Orleans the images are stunning and will help you
understand exactly what is happening to the region. (If you don't have
Google Earth, get it! It is a free download.)
In many ways the MRGO was the most devastating contributor to the wrath
of Katrina. You can see it on the map above as the red and yellow line
angling toward the
southeast from the "s" in New Orleans. Before MRGO there was
plenty of land to the east of
the
city. MRGO killed the St. Bernard marshland and exposed the eastern
flank of the city. The Corps says the "Hurricane Highway" effect
was not achieved during Katrina however computer models show an
acceleration of the surge from Lake Borgne between the MRGO levee and
the GIWW levee to the north into the IHNC.
(IMHO - Tree huggers killed the
nuclear power program in America much to the detriment of the nation but they failed to
kill this waterway much to the detriment of New Orleans.)
But that is only about 1/10th of the story. The other 9/10's are that
the river levees are killing the wetlands to the south and west of the
city.
- Saltwater incursion is killing the vegetation that holds the soil together. The saltwater is getting in because of:
- Subsidence (primarily from lack of new sedimentation)
- Lack of freshwater (the levees insure this too)
- Storms (Katrina took its toll)
- Oil field canals and pipelines
- Increase in sea level (minimal so far)
Two more factors are also reducing the wetlands ability to protect the city:
- Expansion of the city into former wetlands
- Impact
of exotic species like the nutria, imported from South America. With no
natural predators the population has grown unchecked. Nutrias burrow
into banks speeding erosion. They are credited with destroying 65,000
acres of wetlands and are especially bad for levees.
Efforts to increase hunting by introducing the animal to local menus
have been largely unsuccessful because people view these animals as
large unappetizing rats.
When you read the Corps of Engineers timeline of developments in
the Mississippi River Division one point stands out immediately. Their view is that the
main threat is the River. Controlling river flooding is the mission.
The Timeline stretches from 1717 to the present day and the Coastal
Wetlands aren't mentioned until 1990 when someone woke and and realized
they had been shrinking away since the 1930's or before.
New Orleans has been able to thrive and prosper because the wetlands
were there providing protection. Without them the city is exposed.
What has happened to southeast Louisiana is unconscionable. It's as if
Cape Cod has been erased and Boston was exposed to the sea. Would you
complain that the citizens of Boston were foolish for settling in an
exposed area. It's as if Long Island was gone and Manhattan was seaside property. If we leave it unchecked we
will lose the equivalent of the entire state of Maryland off our southern coast.