Geography Reference
In-Depth Information
defense and strategy from the point of view of navigation and colonial control, it
was in no way suited to what was to become an urban agglomeration of over a
million people.
River floods have long been the primary concern. Geologically speaking, the
Mississippi Delta formed very quickly, in less than 6,000 years, thanks to the
enormity of the river and the mass of glacial sediment it carries to the Gulf of
Mexico. Progressive sedimentation at the mouth of the river leads to increased
channel formation during spring flooding. At least four major channels have been
identified, with the current channel dating back approximately to 1100. In 1927, as a
result of extensive flooding in the Mississippi catchment, the river nearly shifted
courses west to the faster flowing, more direct channel to the sea, which follows the
Atchafalaya River. This shift would have meant the end of the ports of New Orleans
and Baton Rouge and the transformation of the lower Mississippi into a slow-
moving bayou. The construction of the Old River Control Structure, 200 km
northwest of New Orleans, anticipated the inevitable deviation, channeling 30% of
Mississippi River water into the Atchafalaya River. The United States Army Corps
of Engineers (known as the Corps) built the flood control system and reinforced the
levee protection to 7.6 meters, a strategy that proved successful in preventing
flooding of the lower Mississippi. Storm surges, such as those produced by gale-
force winds moving over water, represent a significant additional flooding risk along
the lower Mississippi. While the original New Orleans settlement was built on high
ground, and was therefore protected from storm surges, this was not the case for the
marshes surrounding these high grounds. Surrounding marshes act like a sponge to
protect the city from the storm surge. This natural balance, however, was upset by
twentieth-century urban settlement. It could even be said that responsibility for the
Hurricane Katrina disaster lies entirely with post-1927 development.
9.1. The physical components of natural hazards
At dawn on Monday August 29, 2005, Hurricane Katrina, a Category 4 hurricane
with winds of 235 km/hour, made landfall on the Mississippi Delta, just east of New
Orleans. While the city had been partially evacuated, and it was thought to be safe
from the worst of the storm, swirling hurricane winds pushed Lake Pontchartrain
water into the canals that crisscross the city, causing the collapse of flood walls.
These are the facts which led to the apocalyptic images of bodies floating in the
streets, of desperate men, women, and children driven to the rooftops of submerged
houses, of looting, and of the nearly 20,000 evacuees who took shelter in a stadium
the roof of which was torn away by gale force winds. The most striking feature of
these images is that they mostly showed African-Americans. The reality of racial
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