Convert to Dimensional Susp Sediment, Bedload Rating Curve

This is accomplished by multiplying the bankfull discharge and sediment values obtained at Step 12 times each of the ratios appropriate for the relation selected in Step 13. Previously reported examples of a dimensionless ratio suspended sediment rating curve (Figure 56) and a dimensionless ratio bedload rating curve (Figure 57) are used to convert to dimensioned rating curves. Examples of suspended sediment and bedload rating curves (dimensioned) are shown in Figure 119 (PDF, 18 kb, 1 p.) and Figure 120 (PDF, 195 kb) for the Weminuche River in Southwestern Colorado. Tests of this relation were reported in Figures 58 through 61, where reference dimensionless rating curves were used to establish sediment rating curves.

Figure 58 (PDF, 78 kb, 1 p.)
Figure 59 (PDF, 57 kb, 1 p.)
Figure 60 (PDF, 62 kb, 1 p.)
Figure 61 (PDF, 53 kb, 1 p.)

If it is not possible to obtain measured bankfull discharge, suspended sediment and bedload sediment, to convert dimensionless sediment rating curves to actual values, then the use of regional curves could be temporarily substituted. The user must obtain drainage area in square miles to obtain bankfull discharge from a similar hydro-physiographic province (Figure 100) (PDF, 48 kb, 1 p.). The bankfull flow is used to convert the dimensionless flow-duration to dimensioned flow-duration. The bankfull discharge is also used to convert the dimensionless discharge portion of the dimensionless suspended and bedload rating curve to actual values. The sediment data obtained from drainage area must be derived from existing measured bankfull suspended sediment and bedload sediment data, then converted to unit area sediment values from the corresponding drainage area. These data need to represent the same lithology, stream type and stability condition of the stream being predicted.

An example of unit area suspended sediment data from USGS sites throughout the United States is shown in Simon et al. (2004). These measured sediment values were separated by evolutionary stages, thus additional stability/stream type data may help in identifying appropriate relations for extrapolation. This drainage area extrapolation procedure represents only an interim procedure until measured bankfull values can be obtained.

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