Appendix A: A Practical Guide to Effective Discharge Calculations
Batupan Bogue
100
10
1
0.1
0.01
0.001
0.0001
0.001
0.01
0.1
1
10
Q / Q2
USGS Gauge Data
Regionalized Discharge Index for DEC Watersheds, Mississippi (adapted from Watson et
Figure 3
al., 1997)
Watson et al. (1997) tested the accuracy of these approaches. They found that the average error
in bed material sediment yields at all the ungaged sites tested was only 2.8% when the method was used
to transfer a flow duration relationship within a watershed, and 5.5% when it was used to develop a
regional flow duration relationship.
SEDIMENT TRANSPORT DATA AND CALCULATIONS
Nature of the Sediment Load
The total sediment load of a stream can be broken down on the basis of measurement method,
transport mechanism or source (Table 1). The transport of bed material load can be classified as bedload
dominant, mixed load or suspended load dominant on the basis of the ratio of shear velocity to fall velocity
(Julien, 1995). If this ratio is less than about 0.4, bedload is dominant. Between about 0.4 and 2.5, bed
material loads move as a mixture of bedload and suspended load. Above about 2.5, suspension is the
dominant transport mechanism. When discussing the sediment load of a stream, it is important to keep
track of the terminology adopted and the nature of the load being discussed.
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