3)

Plot Bed Material Load Data

The bed material load (y-axis) is plotted as a function of discharge (x-axis) in a scattergraph, with

both axes on logarithmic scales, carefully matching the units of sediment load to the time base for the

discharge frequency distribution.

4) Determine Sediment Rating Curve

A power function best-fit regression line should be fitted to the data in the scatter graph to produce

a bed material load function of the form:

Qs = aQb

(1)

where, Qs = bed material load discharge, Q = water discharge, a = regression constant, and b = regression

coefficient.

1)

Calculate Representative Discharges

The discharges used to generate the bed material load histogram are the mean discharges in each

class of the flow frequency distribution. If discharge class intervals are arithmetic, the representative

discharges are the arithmetic means of each class. If the discharge class intervals are logarithmic, the

representative discharges are the geometric means of each class.

2)

Construct the Bed Material Load Histogram

The bed material transport rate for each discharge class is found from the rating curve equation.

This load is multiplied by the frequency of occurrence of that discharge class to find the total amount of bed

material transported by that discharge class during the period of record. Care should be taken to ensure

that the time units in the bed material load rating equation are consistent with the frequency units for the

distribution of flows. The results are plotted as a histogram.

3)

Find the Effective Discharge

The bed material load histogram should display a continuous distribution with a single mode (peak).

If this is the case, the effective discharge corresponds to the mean discharge for the modal class (that is the

peak of the histogram). If the modal class cannot be readily identified, the effective discharge can be

estimated by drawing a smooth curve through the tops of the histogram bars and interpolating the effective

discharge from the peak of the curve.

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