Figure 13 shows the calculation results for Test R2, which encompassed
blocking of a majority of the waves before incipient breaking. (However,
because random waves were employed, breaking would occur for some
waves.) The shoaling phase is well described and in agreement with trends
obtained for the monochromatic waves. Also, it seems like the recorded
typical blocking point is shoreward of the simulated one. The maximum rms
wave height is overestimated by about 20 percent, which was the case for
some monochromatic tests as well (compare Figure 9). The simulation
results for Test R4 display similar characteristics as the results for Test R2
(see Figure 14).
Test R15 shows some breaking before blocking is calculated to occur, but
otherwise displays the same tendencies as Tests R2 and R4 (Figure 15).
However, the conditions for Test R19 were such that wave blocking was not
the simulations together with the measurements. Again, the maximum rms
wave height is overestimated, and the discrepancy in the shoreward portion
of the profile is marked. The poor description in the shoreward area owes to
the fact that a majority of the waves is not calculated to break on the current,
implying that they propagate to the area of maximum current without losing
energy. Some waves break, but dissipate their energy down to the stable
wave height fairly quickly, giving a constant wave height in the shoreward
part of the profile. The Monte-Carlo simulation technique with constant
wave period is one reason for the discrepancy between calculations and
measurements. In shallow water (e.g., the CHL-I data), the influence of wave
period is not as pronounced as in deep water, making it more reasonable to
only employ one period in the simulations for the CHL-I data.
Effects of Including Roller
To represent the dependence of the momentum transport of the roller on
the cross-shore wave height distribution, the wave energy balance equation
(Equation 31) was included in NMLong-CW. Thus, Equation 32 was solved
after the wave action equation to yield the momentum fluxes associated with
the roller in the cross-shore and longshore directions. Relative wave
quantities were employed in the roller equation to account for the wave-
current interaction. However, before applying the enhanced model to the
CHL-I and C&K data sets, sensitivity tests were carried out, including both
monochromatic and random waves. Monochromatic waves occasionally
caused numerical instability, because the break point represents a
discontinuity in the forcing. This problem and how it was circumvented is
discussed in the chapter dealing with modeling the longshore current. For
random waves, the forcing constitutes a smooth function across the profile,
and no difficulties were encountered in such simulations.
In the CHL-I and C&K experiments, the waves propagated across the
profile (i.e., perpendicular to the shoreline), and the only manifestation of
including the roller would be on the mean water level. In test simulations for
these two data sets, the mean water level was only marginally changed by
including the roller momentum, which in turn did not noticeably change the
wave height distribution across the profile. In comparing, calculated mean
water level from NMLong-CW simulations with and without roller, the
simulations with the roller displayed the expected shoreward shift in the
water level shape.
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Chapter 4 Verification of Wave Model