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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lateral shifting of the channel before stability is restored. The reaction of a channel
to changes in discharge and sediment load may result in channel dimension changes
contrary to those indicated by many regime equations. For example, it is
conceivable that a decrease in discharge together with an increase in sediment load
could actuate a decrease in depth and an increase in width.

Thalweg Length
Sinuosity:
Valley Length

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Choni'll I

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Thalweg
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Slr(U9hl

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arOldld

Slope -

Fig. 1.2.2 Sinuosity vs slope with constant discharge.

Changes in sediment and water discharge at a particular point or reach in a
stream may have an effect ranging from some distance upstream to a point
downstream where the hydraulic and geometric conditions will have absorbed the
change. Thus, it is well to consider a channel reach as part of a complete drainage
system. Artificial controls that could benefit the reach may, in fact, cause
problems in the system as a whole. For example, flood control structures can cause
downstream flood damage to be greater at reduced flows if the average hydrologic
regime is changed so that the channel dimensions are actually reduced. Also, where
major tributaries exert a significant influence on the main channel by introducing
large quantities of sediment, upstream control on the main channel may allow the
tributary to intermittently dominate the system with deleterious results. If

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