Environmental Engineering Reference
In-Depth Information
Many dams and reservoirs have been built on tributaries to hold back
and store water. Some of the dams burst under the onslaught of the
raging waters. Much of the river has been lined with concrete slabs but
even these could not restrain the waters.
Engineers, hydrologists, and environmentalists agree that the efforts
of the U.S. Army Corps of Engineers to control the Mississippi have only
made things worse. They have cut through meanders and shortened the
river, causing it to fl ow more quickly and increase erosion. By restricting
the fl ow of water inside the levees, they have speeded up the fl ow and
increased the pressure on the levees, which increases their chance of
failing. And they have altered the natural fl ow of the river so that the
1993 fl oods were the worst ever, even though there was less water in the
river than during previous major fl oods. And the levees have been poorly
built in many places.
7
Red River, North Dakota Flood, 2009
Not all river fl oods are caused or made worse by human foolishness.
Some result from the age of the river, the local topography, and the
geological history of the area. An example of this is the fl ood the last
week in March 2009 on the Red River in North Dakota. The river, which
separates North Dakota and Minnesota and fl ows north into Canada, is
fairly modest in size compared with more famous rivers such as the Mis-
souri and Mississippi. But it has a behavior that is hard to predict. The
National Weather Service did, however, rate the area along the border
separating North Dakota and Minnesota as an area of extreme fl ood
risk only a week before the fl ood occurred (fi gure 3.1). The Weather
Service reported that “copious precipitation during the fall, wet soils
before freeze-up, and areas of substantial water in the snow pack have
produced an imminent risk of major fl ooding along the Red River. . . .
Major overland fl ooding is expected in eastern North Dakota and north-
west Minnesota beginning the week of Sunday, March 22. This will
subsequently lead to major, and possibly record, fl ooding along the Red
River of the North and its tributaries.” If only all government agencies
were that specifi c and that correct.
The Red River fl ows across the fl at bottom of a dried-up glacial lake
that was created from meltwaters at the end of the last glacial episode.
The river, only about 9,300 years old, is normally small and shallow,
and it fl ows slowly across a fl at landscape. It has not had the time or
energy to cut deep channels that can contain water during fl oods. The
river has cut a shallow sinuous valley across one of the fl attest expanses
