Range of Solutions
Stable channel dimensions are calculated for a range of widths. For each
combination of slope and base width, a unique value of depth is calculated. This
can be used to evaluate stability in an existing channel or in a proposed design
channel. It is important to consider river morphology when interpreting these
calculated values. It is important to be consistent in the selection of channel
dimensions. That is, once a width is selected, the depth and slope are fixed. This
allows the designer to select specific project constraints, such as right-of-way,
bank height or minimum bed slope, and then arrive at a consistent set of channel
dimensions.
If the calculations indicate that the slope of the project channel needs to be
less than the natural terrain, the slopes in the table can be used to aid in spacing
drop structures or introducing sinuosity into the project alignment.
An example of a family of slope-width solutions that satisfy the resistance and
sediment transport equations for the design discharge is illustrated by Figure
6.18. Any combination of slope and base width from this curve will be stable for
the prescribed channel design discharge.
result in degradation, and combinations below the curve will result in
aggradation. The greater the distance from the curve, the more severe the
instability.
45
40
35
30
25
20
15
0
50
100
150
200
250
Bottom Width, Feet
Q = 2680
Figure 6.18. Example slope-width graph from the stable channel dimensions
calculations.
Constraints on this wide range of solutions may result from a maximum
possible slope, or a width constraint due to right-of-way. Maximum allowable
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Chapter 6
Input Requirements and Program Output for SAM.hyd
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