Environmental Engineering Reference
In-Depth Information
27 percent of the major roads, 9 percent of the rail lines, and 72 percent
of the ports in the area are built on land at or below 4 feet in elevation,
a level within the range of projections for sea-level rise in this century.
And, as noted in chapter 9, this level is likely to be reached before the
end of the century. Before then, increased storm intensity may lead to
more service disruption and infrastructure damage. More than half of
the area's major highways (64 percent of the interstates, 57 percent of
arterials), almost half of the rail miles, twenty-nine airports, and virtually
all of the ports are below 23 feet in elevation and subject to fl ooding
and damage due to hurricane storm surge.
Engineers have been trying for 200 years to restrain the Mississippi
River's natural urge to move sideways, change its meander pattern, and
otherwise display its power. Artifi cial levees were built to protect cities
and farmland from fl ooding. In effect, engineers have been trying to fi t
a straitjacket to a moving target, and they have not had great success.
In 2007 offi cials in Louisiana proposed to spend what will amount to
hundreds of billions of federal dollars in a far-reaching plan to cause a
major rerouting of the southern end of one of the world's major water-
ways.
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If the rerouting plan is approved, it would be one of the great
engineering challenges of this century. Whether such an ambitious plan
could be completed in time to save annually threatened communities in
southern Louisiana is questionable. Given the inevitable political and
fi nancial delays that always accompany ambitious federal projects, the
area might well be underwater before rerouting occurs.
The plan would allow the Mississippi to fl ow out of its levees in more
than a dozen places in Louisiana and would create new waterways at
seven or more sites that would carry a volume of water similar to or
greater than that of the Potomac River (2 percent of Mississippi River
discharge at New Orleans). Sediment from these new rivers would carry
the water and land-enhancing sediment into eroding coastal areas. Other
plans call for mechanically pumping sediment to rebuild marshes and
barrier islands. Hundreds of miles of new or reconstructed levees would
add fl ood protection.
It is noteworthy that abatement plans in the United States are designed
to withstand fl oods or storms that would occur statistically once every
30 to 100 years. (As noted earlier, these estimates seem to underesti-
mate fl ood frequencies.) The Netherlands, a country that has half its
land at or below sea level, builds its levee and dike systems to with-
stand a 1,250-year fl ood, though rising sea levels and increasing storm
intensities have made even this degree of protection suspect. The past
