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.

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.

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.

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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