4 Theoretical Basis for SAM.yld
Calculations
Purpose
Sediment yield is the total sediment outflow from a watershed or drainage
basin, measurable at a cross section of reference and in a specified period of time
(ASCE, 1975). Sources of the total sediment yield include the watershed
surface, rills and gullies, streambanks, and degrading streambeds. Sediment
yield can be subdivided based on the method of transport. The finer portion of
the sediment yield is continuously maintained in suspension by flow turbulence
and is called the washload. The coarser fraction of the sediment yield is actively
exchanged with the sediment on the bed and is called the bed-material sediment
yield. SAM.yld provides hydraulic design engineers a systematic method for
rapidly calculating sediment yield. If sediment transport is calculated using
sediment transport equations, only the bed-material sediment yield is calculated.
If sediment transport is determined from total load measurements, then the total
sediment yield (washload and bed-material load) is calculated.
General
SAM.yld calculates sediment yield passing a cross-section during a specified
period of time. The time period considered can be a single flood event or an
entire year. In SAM.yld the flow can be specified by either a flow duration curve
or a hydrograph. The sediment discharge curve can be specified as either
sediment discharge versus water discharge or as sediment concentration versus
water discharge. Calculations are based on the flow-duration sediment-discharge
rating curve method.
Flow-Duration Sediment-Discharge Rating Curve
Method
This is a simple integration of the flow duration curve with the sediment
discharge rating curve at the outflow point from the drainage basin. This method
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Chapter 4
Theroetical Basis for SAM.yld Calculations
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