ERDC/CHL CHETN-II-46
March 2002
empirical coefficient. Based on the original field study by Komar and Inman (1970), the Shore
Protection Manual recommends a Kl value of 0.39. Bodge and Kraus (1991) re-examined the
derivation and suggested a lower Kl value of 0.32. Schoonees and Theron (1993, 1994) re-
examined the 46 most reliable of the 240 existing field measurements that have been compiled
and recommended a Kl value of approximately 0.2. In a number of GENESIS model
applications, where calibration involves adjustment of the Kl value to maximize replication of
observed shoreline changes and net and gross LST rates based on local knowledge of the
sediment budget, optimal Kl values often range from 25 to 50 percent of the value recommended
in the Shore Protection Manual.
Based on similar field data, Kamphuis et al. (1986) developed an empirical formula that includes
the beach slope and sediment grain size,
H s3b.5m
sin(2θb )
Q = 1.28
(2)
d
where, d is sediment grain size, and m is beach slope. Based on a series of laboratory studies and
re-examination of existing field data, Kamphuis (1991) suggested an empirical formula for the
prediction of total longshore sediment transport rate, modifying the 1986 formula and adding the
influence of peak wave period, Tp
Q = 6.4 104 H s2b Tp1.5m0.75d -0.25 sin 0.6 (2θb )
(3)
It is noted that the dependence on grain size and wave height are greatly reduced as compared to
Equation 2. The influences of beach slope and incident wave angle are also reduced. The
coefficients in the preceding Kamphuis-86 and -91 formulas were determined using metric units.
Wang, Kraus, and Davis (1998) found that the Kamphius-91 formula predicted consistently
lower total longshore transport rates than those predicted by the broadly used CERC formula and
the Kamphuis-86 formula. The relatively lower prediction by the Kamphuis-91 formula, which
is typically 1.5 to 3.5 times lower than predictions from the CERC and Kamphuis-86 formulas,
occurred over a range of low wave-energy conditions with breaker heights of less than 1 m
(Wang, Kraus, and Davis 1998). However, the lower predictions by the Kamphuis-91 matched
the measured values closer than the CERC formula predictions for those low-wave conditions.
Lower predictions also occurred for storm conditions with breaker heights of nearly 4 m (Miller
1998). However, Miller found that predictions by the CERC formula matched the measured
rates closer than the Kamphuis-91 predictions, which were nearly one order of magnitude lower
than the measured values.
The effect of breaker type on the rate of LST, and its cross-shore distribution is poorly
understood. One of the more commonly used indicators of breaker type is the surf similarity
parameter, ξb, which is defined as
m
ξb =
(4)
H brms / Lo
2
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