80
A. Bayram et al. / Coastal Engineering 44 (2001) 7999
mulas are assessed, as well as their limitations, using
1. Introduction
various statistical measures. Finally, the conclusions
of the study are presented in Section 6.
During the past three decades, numerous formulas
and models for computing the sediment transport by
waves and currents have been proposed, ranging from
quasi-steady formulas based on the traction approach
2. Longshore sediment transport formulas
of Bijker, and the energetics approach of Bagnold, to
Longshore sand transport is typically greatest in
complex numerical models involving higher-order
the surf zone, where wave breaking and wave-induced
turbulence closure schemes that attempt to resolve
currents prevail, although a pronounced peak can be
the flow field at small scale. There are relatively few
found in the swash zone as well (Kraus et al., 1982).
high-quality field data sets on the cross-shore distri-
Typically the total (or gross) longshore sediment
bution of the longshore sediment transport rate avail-
transport rate is computed with the CERC formula
able to evaluate existing predictive formulas. Kraus et
(SPM, 1984) in engineering applications. However, as
al. (1989) and Rosati et al. (1990) measured the
ability to predict the surf zone hydrodynamics has
longshore transport rate across the surf zone using
improved, the need for reliable formulas that spatially
streamer traps (i.e., DUCK85 and SUPERDUCK field
better resolves the sediment transport rate has
experiments). Miller (1999) measured the cross-shore
increased, both concerning the cross-shore distribu-
distribution with optical backscatter sensors (OBS)
tion of the transport rate and the concentration dis-
combined with current measurements (i.e., SANDY-
tribution through the water column.
DUCK field experiment). The measurements reported
In this investigation, the skill of six published
by Miller (1999) covered a number of storms, thus
formulas proposed for calculating the cross-shore
complementing the measurements by Kraus et al.
distribution of the longshore sediment transport rate
(1989) and Rosati et al. (1990) that were made in
was investigated. Transport rates were calculated for
milder swell waves.
the utilized cases using standard coefficient values (as
The objective of the present study is to evaluate the
given in the literature) without calibration. In the
predictive capability of six well-known sediment
present comparison the formulas proposed by Bijker
transport formulas, adapted to calculate the cross-
(1967, 1971), Engelund and Hansen (1967), Ackers
shore distribution of the longshore sediment transport
and White (1973), Bailard and Inman (1981), Van
rate, based upon the above-mentioned three field data
Rijn (1984), and Watanabe (1992) (as they chrono-
sets. We selected formulas that have gained world-
logically appeared in the literature) were employed,
wide acceptance in confidently predicting longshore
representing the most common approaches for calcu-
sediment transport rates. This, however, should not be
lating the time-averaged net sediment transport rate.
interpreted as a sign of disagreement or a lessening of
The Bijker and Van Rijn formulas also calculate the
the importance of formulas not discussed here. Only
suspended sediment concentration distribution
sand transport was investigated in this study, and
through the water column, which allowed for addi-
focus is on computing the time-averaged net long-
tional comparisons for these two formulas with some
shore transport rate.
of the field cases for which concentration measure-
Background to the investigated sediment transport
ments were made. This will be discussed in a forth-
formulas are given in Section 2 and their main
coming paper (Larson et al., in preparation).
characteristics are summarized (the equations used
The six formulas are summarized in Table 1, where
to calculate the transport rate are given in Appendix
the formulas, coefficient values, and wave and beach
A). Next, in Section 3, the longshore sediment trans-
conditions of the data originally used for verification
port data sets are described. In Section 4 are shown
of the formulas are listed. Further details regarding the
the results of the comparisons between the formulas
equations are given in Appendix A. This is necessary
and the field data including a wide range of wave and
because some variants of the formulas have appeared
current conditions. An overall discussion of the results
in the literature. In the following, a short background
from the comparisons is provided in Section 5, where
to the formulas is presented together with their main
the strength and weaknesses of the investigated for-
Previous Page
