Environmental Engineering Reference
In-Depth Information
3
Floods: When the Levees Break
The river belongs to the Nation,
The levee, they say, to the State;
The Government runs navigation,
The commonwealth, though, pays the freight.
Now, here is the problem that's heavy-
Please, which is the right or the wrong-
When the water runs over the levee,
To whom does the river belong?
—
Douglas Malloch,
Uncle Sam's River,
1912
Two of the worst naturally occurring environmental disasters in U.S.
history are the 1993 fl ood in the Mississippi River and the 2005 fl ooding
in New Orleans that resulted from hurricanes Katrina and Rita. Each of
these fl oods was extremely costly, causing tens of billions and even hun-
dreds of billions of dollars in damage, as well as loss of life and property.
Worldwide since 1980, hurricane numbers have nearly doubled, and the
frequency of fl oods has more than tripled.
1
These data give rise to the
suspicion that climate changes may be the cause of the increases. Both
hurricanes and river fl oods are strongly correlated with climate. In the
United States, fl oods account for about 60 percent of federally declared
disasters.
Floods can sometimes be predicted but rarely can be prevented. Pre-
ventive measures such as dams and levees are often inadequate and are
commonly overridden by surging waters. Analyses reveal that water
levels for 100-year fl oods are profoundly underestimated by fl ood spe-
cialists.
2
At many sites in Iowa and Missouri, the fl ood of 2008 neared
or exceeded the record 200-year or 500-year levels attained in the record
Midcontinent fl ood of 1993. There are numerous examples of repeated
inundations over brief periods by fl oods expected only once in hundreds
