Fundamentals of Engineering Design
Colby
Brownlie, D50
Laursen (Madden)
Laursen (Copeland)
Profitt (Sutherland)
The sediment transport module can be used to develop sediment rating curves from any of the 19
equations. A sediment rating curve yields the sediment transport rate as a function of discharge rate. An
example of a sediment rating curve is given in Figure 5.37. The selection of an appropriate sediment
transport equation should be based on the range of particle sizes in the bed material and the flow conditions
being investigated.
5.3.6.2 Sediment Yield Calculations
Sediment yield is the weight of sediment passing a cross-section during a specified period of time
(Thomas et al., 1994). Typically sediment yield is evaluated on an annual bases, but calculations can be
performed for a single event. SAM offers two options for computing sediment yield: the flow duration
curve method and the flow hydrograph method.
The flow duration curve method integrates a flow duration curve with a sediment transport rating
curve to evaluate the total sediment passing the basin outlet. A flow duration curve is a cumulative
distribution function which presents the percentage of time during an average year that a given discharge
is equaled or exceeded. An example flow duration curve is given in Figure 5.38. Sediment transport rating
curves are described in the previous section. SAM uses a log-linear interpolation of the discharge versus
exceedence probability flow duration curve. A log-log interpolation of the sediment transport rating curve
is used. The flow hydrograph method integrates a hydrograph with a sediment rating curve to evaluate
the sediment yield for a given event. A hydrograph is a plot of discharge versus time, Figure 5.39. This
method is used to evaluate the sediment yield for a given event for which the hydrograph is known.
5.3.6.3 Hydraulic Calculations
The hydraulics calculations module in SAM evaluates channel dimensions in both fixed and mobile
bed boundaries. The module calculates channel dimensions by solving the Manning equation, calculating
stable channel dimensions using Copeland's method, and sizing riprap for channel stability.
5.3.6.4 Governing Equations for Stable Channel Design Procedure
Copeland's method for stable channel design is an analytical technique that calculates channel
dimensions by simultaneously solving equations which govern water and sediment continuity. The method
uses Brownlie (1981) for flow resistance and sediment transport equations.
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