Figure 5.10. Plot of River Nile sinuosity and valley slope. Numbers represent reaches of
Figure 5.9. The vertical line joining two points for Reach 12 shows the
difference between 18th century and present low sinuosity (after Schumm and
Galay 1994).
5.3.3 Summary
The contrast between the lower Mississippi River and the Nile is striking. The Nile is much
less dynamic, but it too responds to geologic controls and tributary influences. Both the
Mississippi and Nile Rivers have sand-beds, yet what lies beneath the sand may be of critical
importance to the character and response of these great rivers. It is probable that the
Mississippi is controlled totally by Tertiary-age clay and Pleistocene-age gravels, and the
Nile has apparently developed an armor of gravel and cobbles beneath its sand bed.
Anomalous river behavior can often be explained by factors that are related to river history.
Both the Mississippi and the Nile provide support of this fact. Hence, factors that are
normally beyond the engineer's range of expertise may dominate river morphology and
behavior.
In order to understand alluvial rivers, one cannot limit a study to modern conditions only. In
fact, past channel morphology and behavior can provide valuable information about modern
river behavior. For example, although both the Mississippi and the Nile are large and
transport similar sediments, they differ greatly morphologically and dynamically as a result of
quite different histories. Therefore, in order to anticipate and to predict river response, both
the past and the present must be combined in what could be termed a geomorphic-
engineering approach to river maintenance and/or restoration.
5.4 STREAM FORM AND GEOMETRY OF ALLUVIAL CHANNELS
A study of the plan and profile of a stream is very useful in understanding stream morphology.
Planview appearances of streams are varied and result from many interacting variables. Small
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