Inflowing Sediment Discharge
This is the concentration of the inflowing bed material load. It is best if
SAM.hyd is allowed to calculate the sediment concentration based on hydraulic
conditions in the sediment supply reach. The bed material composition is
defined by the median grain size and the gradation coefficient.
Valley Slope
Valley slope is the maximum possible slope for the channel invert. This value
is used in the test for sediment deposition. If the required slope exceeds the
prescribed valley slope, the following message is printed:
>>>>MINIMUM SLOPE IS GREATER THAN VALLEY SLOPE - THIS IS A SEDIMENT TRAP <<<<
Bank Slopes and Roughness
The analytical method assumes that all bed material transport occurs over the
bed of the cross section and that none occurs above the side slopes. Therefore,
the portion of water conveyed above the side slopes expends energy but does not
transport sediment, making "Flow Distribution" an extremely important
calculation. The input parameters for flow distribution are bank angle and bank
roughness. The recommended procedure to use for this is discussed in Chapter 5
of EM 1110-2-1601 (USACE 1991, 1994). Any roughness input for the bed will
be disregarded by the calculations as bed roughness is calculated using the
Brownlie equations. For maximum transport of sediment, use the steepest bank
angle allowed by bank stability requirements.
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 also 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 or
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 in 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
2.11. Any combination of slope and base width from this curve will be stable for
the prescribed channel design discharge. Combinations of width and slope that
43
Chapter 2
Theoretical Basis for SAM.hyd Calculations
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