profile included a pronounced longshore bar and the maximum current was
typically located in the trough, whereas most of the breaking occurred on the
seaward side of the bar (compare Kuriyama and Ozaki 1993).
Figure 45 compares the calculated (with and without roller) and
measured longshore current distribution together with the beach profile for
Case 100 from Smith, Larson, and Kraus (1993). As for the K&O data, the
peak in the current distribution more or less occurred in the trough, and the
model could not describe this shift entirely, even with the roller model
included. Also, the translation in the forcing induced by the roller model
creates a large peak at the shoreline, which is similar to what the model by
Smith, Larson, and Kraus (1993) produced. Because no measurements were
made in this region, it is difficult to assess how realistic this peak is. Most
moving in the swash. A coarser bed implies a reduced current velocity
compared to using the same cf-value as for the remainder of the profile (as
done in the present calculations). The wave conditions during Case 100 were
Hrms = 0.94 m, Tp = 9.7 s, and α = 32 deg in 8-m water depth, and the
measurements were taken during rising tide (+0.2 m above mean sea level).
Figure 46 compares calculations and measurements for the rms wave height.
Case 1000 from Smith, Larson, and Kraus (1993) was also simulated to
investigate the result for a situation when the tide was falling (water level was
0.40 m below mean sea level). The wave conditions for this case were Hrms =
0.71 m, Tp = 9.7 s, and α = 34 deg (8-m water depth). Figure 47 compares
calculated (with and without roller model) and measured longshore current
for the Delilah field experiment Case 1000, and Figure 48 gives the
corresponding rms wave heights. Because a larger portion of the waves
break on the bar for Case 1000 as compared to Case 100, the forcing for the
current is stronger on the shoreward side of the bar, and the peak in this
region is more pronounced for Case 1000. Thus, because the measured peak
is still approximately located in the trough, the deviation between the
calculations and measurements is larger for Case 1000 than for Case 100.
Even though the roller model translates the calculated current peak
shoreward, the shift is not large enough to produce satisfactory agreement for
the cases where large portions of the waves break on the bar. Simulations
with smaller values of βD and for alternative mixing formulations only
marginally improved the results. The calculated rms wave height is in good
agreement with the measurements, indicating that the predictions of the input
forcing from the waves is estimated with a high degree of accuracy.
Effects of Large-Scale (Tidal) Current on Wave-
Generated Current
To illustrate the capability of NMLong-CW to simulate the action of a
large-scale current on the wave-generated longshore current in the nearshore,
accordance with Dean (1977) was assumed with a shape parameter of A =
0.1 m1/3, corresponding to a median grain size of about 0.2 mm. An rms
wave height in deep water of Hrmso = 2.0 m with a mean period of T = 8.0 s
and a mean incident angle αo = 30 deg were specified (waves Rayleigh
66
Chapter 6 Verification of Longshore Current Model