If sediment inflow is to be calculated, which is the recommended procedure,
additional data are required for the supply reach. This screen is accessed by
clicking the "Define Supply Reach" button on the lower right, Figure 6.15. The
additional input screen, asking for base width, side slope, bank roughness
coefficient, bed-material median grain size geometric gradation coefficient,
average slope, and discharge, is shown in Figure 6.16.
Figure 6.16. Input screen for the Supply Reach for Stable Channel Design
Method Calculations.
For both these sub-data sets, it is important that the base width is
representative of the total movable-bed width of the channel. The bank
roughness should serve as a composite of all additional roughness factors, i.e.,
channel irregularities, variations of channel cross-section shape, relative effect of
obstructions, vegetation, and sinuosity. Only flow that is vertical above the bed
is considered capable of transporting the bed material sediment load.
Specific Input Requirements
Water Discharge The design discharge is critical in determining appropriate
dimensions for the channel. Investigators have proposed different methods for
estimating that design discharge. The 2-year frequency flood is sometimes used
for perennial streams. For ephemeral streams the 10-year frequency is some
times used. The "bankfull" discharge is sometimes suggested. Others prefer
using the "effective" discharge. Currently, there is no generally accepted method
for determining the channel-forming discharge. It is recommended that a range
of discharges be used in the analysis to test sensitivity of the solution. However,
currently SAMwin will calculate for only one discharge at a time.
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.
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Chapter 6
Input Requirements and Program Output for SAM.hyd
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