Figures 1 and 3 show that waves heights from the STWAVE spectral and parametric results are very consistent with
a few larger errors in the parametric results for isolated points (e.g., 1-2 April 1997). The simulated wave heights
(spectral and parametric) are generally smaller than the measurements with the exception of the large overestimate
of wave heights during Hurricane Bonnie in August of 1998 (simulated wave height of 5.2 m and measured wave
height of 3.5 m). The overestimation during Bonnie is also observed in WIS comparisons to Buoy 44014 (30%
overestimate). The larger errors in peak wave period for the parametric results are due to the presence of multiple
wave trains that are not modeled with the parametric approach (all energy is assigned to a single peak). Errors in
mean direction are reduced by approximately one-third by using the spectral approach. The mean directions from
the parametric approach display some large deviations from the measurements and from the spectral approach (20-
60 deg). These errors are the result of multiple wave trains or offshore (WIS) peak directions that are nearly parallel
to the coast.
4.
SEDIMENT TRANSPORT CALCULATIONS
The result of interest for most coastal processes investigations is not the waves, but the sediment transport generated
by breaking waves. The STWAVE simulations are not of sufficient spatial resolution to determine breaking wave
parameters for longshore sediment transport calculations. To estimate longshore energy flux at incipient breaking,
STWAVE spectra from the 8-m depth (8-m array location) were linearly refracted and shoaled across a typical one-
dimensional beach profile. Wave breaking was implemented using the dissipation function of Battjes and Janssen
(1978),
D = 0.25Qb f m ( H max ) 2
(4)
H max = 0.14L tanh(kd )
(5)
where
D
=
energy dissipation
=
percentage of waves breaking based on a truncated Rayleigh distribution of wave heights
Qb
fm
=
mean frequency
L
=
k
=
wave number
d
=
water depth
A single typical beach profile was used for the full 2 years (Figure 5). The longshore energy flux, Pls, was
calculated based on the Shore Protection Manual (1984) by integration over the spectrum as
Pls = ρg ∫∫ C g Edf sin 2αdα
(6)
where
ρ = mass density of water (1000 kg/m3, fresh water)
Cg = wave group celerity
The energy flux was calculated at incipient breaking, as defined by the most seaward location where Qb = 0.01 (or
where 1% of the waves are breaking). This is approximately the location where the wave height is largest.
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