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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A study by Schmuddle (1963) shows that about one-third of the floodplain of the
Missouri River over the 170-miIe reach between Glasgow and St. Charles, Missouri,
was reworked by the river between 1879 and 1930. On the Lower Mississippi River,
bend migration was on the order of 2 feet per year, whereas in the central and upper
parts of the river, below Cairo, it was at times 1000 feet per year (Kolb, 1963). On
the other hand, a meander loop pattern of the lower Ohio River has altered very
little during the past thousand years. (Alexander and Nunnally, 1972).
Althouqh the dynamic behavior _ of perennial streams is impressive,___lhe
!nodification of rivers in arid and semi-arid reqions and especially of ephel!leral
(flowinq occasionally) stream channels is startlinq. A study of floodplain vegetation
and the distribution of trees in different a'Je ']roups led E-veritt (I968) to the
conclusion that about half of the Little Missouri River floodplain in western North
Dakota was reworked in 69 years.
Historical and field studies by Smith (1940) show that floodplain destruction
occurred dur~ing major floods on rivers of the Great Plains. As exceptional example
of this is the Cimarron River of Southwestern Kansas, which was 50 feet wide during
the latter part of the 19th and first part of the 20th centuries (Schumm and Lichty,
1957). Following a series of major floods during the 1930's it widened to 1200 feet,
and the channel occupied essentially the entire valley floor. During the decade of
the 1940's a new floodplain was constructed, and the river width was reduced to
about 500 feet in 1960. Equally dramatic changes of channel dimensions have
occurred along the North and South Platte Rivers in Nebraska and Colorado as a
result of man's control of flood peaks by reservoir construction. Natural changes of
this magnitude due to changes in flood peaks are perhaps exceptional, but emphasi"e
the mobility.of rivers and their ability to adapt to changing conditions.
Another somewhat different type of channel modification which testifies to the
rapidity of fluvial processes is described by Shull (1922, 1944). During a major flood
in 1913, a barge became stranded in a chute of the Mississippi River near Columbus,
Kentucky. The barge induced deposition in the chute and an island formed. In 1919,
the island was sufficiently large to be homesteaded, and a few acres were cleared
for agricultural purposes. By 1933, the side channel separating the island from the
mainland had filled to the extent that the island became part of Missouri. The
island formed in a location protected from the erosive effects of floods but
susceptible to deposition of sediment during floods. For these reasons the channel
filling was rapid and progressive. It cannot be concluded that islands will always

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