Geography Reference
In-Depth Information
activities were particularly intense between 1950 and 1982, after which oil and gas
production declined due to the depletion of deposits. The extraction of minerals
from the subsoil, and salt water intrusion through the extensive networks of canals
servicing drilling platforms, significantly altered the delicate ecological balance,
adding coastal habitat erosion to the problem of subsidence. The joint effect of
subsidence and coastal erosion was the acceleration of the loss of marsh land by as
much as five times the natural rate.
A University of Florida research team, in a study published in
Nature
[DIX 06],
showed that the average rate of subsidence in the New Orleans metropolitan area is
6 mm/year. With an average rise in mean sea level of 2 mm/year, this would
produce a relative loss in elevation of 8 mm/year. The Congressional report on the
failure of flood control infrastructure as a result of Hurricane Katrina showed that,
over time, barrier elevations had subsided an average 0.6 m from projected control
heights.
Furthermore, the draining of surrounding marshes caused subsidence to
urbanized land. Once encircled and drained, new neighborhoods found themselves
immediately over 0.5 meters below sea level, while neighboring marshes are more
or less at zero. This is why 80% of metropolitan New Orleans is now below sea
level.
The intra-coastal shipping channel serving the Port of New Orleans is called the
Mississippi River-Gulf Outlet (MRGO
3
). The channel was dredged in the 1960s by
the Army Corps of Engineers to foreshorten Gulf of Mexico access for the Port of
New Orleans (120 km via the Mississippi River). The project destroyed nearly
11,000 ha (42.5 square miles) of tidal marshes and opened a 30 km (18.6 mile)
straight-line waterway between Lake Borgne and the Industrial Canal at the heart of
the city. By 1996, significant controversy surrounded this infrastructure, including
dredging costs of $16 million per year for traffic of less than one ship per day.
Excessive delays at the Mississippi River-Industrial Canal lock made MRGO access
slower than if the ship had sailed up the Mississippi River. The MRGO has been
described as a “hurricane highway”. It accelerated destruction of the marshes around
Lake Borgne, the effects of which were all too evident with the passage of Hurricane
Katrina when a storm surge of 4.5 m rushed through the MRGO to overwhelm the
floodwalls protecting New Orleans' eastern neighborhoods.
3
. Is said and read as “Mister GO”.
