FLOOD06421

• County: Statewide
• Basin: Statewide
• Title: Highways in the River Environment
• Date: 2/1/1990
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Evidence from several sources demonstrate that river channels are continually
undergoing changes of position, shape, dimensions, and pattern. In Fig. I.Z.1 a
section of the Mississippi Ri'/er as it was in 1 BB4 is compared with the same section
as observed in 196B. In the lower 6 miles of river, the surface area has been reduced
approximately 50 percent during this B4-year period. Some of this change has been
natural and some has been the consequence of river development work.

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1884

Fig. 1.2.1

Comparison of the IBB4 and 196B Mississippi River Channel
near Commerce, Missouri.

In alluvial river systems. it is the rule rather than the exception that banks will
erode, sediments will be df,posited and floodplains. islands. and side channels will
underqo modification with time. Changes may be very slow or dramatically rapid.
Fisk's (1944) report on the Mississippi River and his maps showing river position
through time are sufficient to convince everyone of the innate instability of the
Mississippi River. The Mississippi is our largest and most impressive river and
because of its dimensions it has sometimes been considered unique. This is, of
course, not so. Hydraulic and geomorphic laws apply at all scales of comparable
landform evolution. The Mississippi may be thought of as a prototype of many rivers
or as a much larger than prototype model of many sandbed rivers.