displays several data sets that "matched" a user's data, all with the same matching
screening parameters.
Criteria for selecting sediment transport functions
Discrepancy ratios were calculated for each measured discharge. Raphelt
(1996) describes the discrepancy ratio that Yang (1984), van Rijn (1984) and
others have used as
qs computed
qs measured
For each data base, the percentage of discrepancy ratios between 0.5 and 2.01
was determined, and the average discrepancy ratio was calculated. The five to
eight sediment transport functions with the highest percentage of discrepancy
ratios within the selected range were selected first. From these, the functions
were ranked by average discrepancy ratio. The function with the discrepancy
ratio closest to 1.0 was ranked highest.
Only one of the Toffaleti function combinations was considered in each
ranking. For instance, if both the Toffaleti and the Toffaleti-Schoklitsch
functions ranked in the top three, only the function with the highest ranking
would be included in the final recommendations. For some functions, sediment
transport is calculated two ways: 1) assuming a median grain size and 2) making
calculations by size class fractions. For these functions only the multiple grain
size option was considered in the rankings. Since the Brownlie function
calculates sediment transport using only the median grain size, it is included in
the rankings.
In some cases, when the data is clearly outside the range for which a sediment
transport function was developed, a function was excluded from the rankings.
The rankings for all the sediment transport functions in SAM.sed, for all the
data sets in SAM.aid, are given in tables 5.2 through 5.21. They are also
available onscreen in SAM.aid as part of the site description, allowing the user to
apply personal engineering judgement and experience. This is an important
feature to remember since the results of SAM.aid are meant only as suggestions,
for guidance.
1
This range, 0.5 to 2.0 was chosen because it is the range that is used in many
other researchers in this field: van Rijn (1984a), Alonso (1980), White, Milli and Crabbe
(1975), among others.
63
Chapter 5
Theoretical Basis for SAM.aid