River Profiles and Bed Material

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The hydraulic geometry relations are applicable to continuous channel behavior. In some

cases, this behavior (in this case the slope) may become discontinuous as the channel pattern

changes from meandering to braided by the formation of cutoffs. Application of Equation 5.13

is illustrated with field data in Section 5.9 (Problem 7).

5.5 QUALITATIVE RESPONSE OF RIVER SYSTEMS

Many rivers have achieved a state of practical equilibrium throughout long reaches. For

practical engineering purposes, these stable reaches can be also called "graded" streams by

geologists and "poised" streams by engineers. However, this does not preclude significant

changes over a short period of time or over a period of years. Conversely, many streams

contain long reaches that are actively aggrading or degrading. These aggrading and

degrading channels pose a definite hazard to any highway crossing or encroachment, as

compared to poised streams.

Regardless of the degree of channel stability, local human activities may produce major

changes in river characteristics locally and throughout the entire reach. All too frequently the

net result of a river improvement is a greater departure from equilibrium than that which

originally prevailed. Good engineering design must invariably seek to enhance the natural

tendency of the stream toward stable conditions. To do so, an understanding of the direction

and magnitude of change in channel characteristics caused by human activity and natural

processes is required. This understanding can be obtained by: (1) studying the river in a

natural condition; (2) having knowledge of the sediment and water discharge; (3) being able to

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