layer was not included). Kuriyama and Ozaki (1993; see also Kuriyama and
Nakatsukasa 1999) developed a model of the longshore current and employed
it to simulate the K&O data. Their calculations involved more elaborate
methods to derive the input wave conditions, and they obtained better
agreement for the cross-shore distribution of the wave height.
Trial calculations were also performed by varying values on the roller
dissipation coefficient βD. Figure 44 illustrates the result for βD = 0.05 and
0.1. As for the simulations with the K&S data, reducing the value on βD
somewhat improves the agreement between calculations and measurements.
However, any reasonable lowering of βD does not reproduce the large value
on the current recorded in the middle of the trough. To obtain such strong
currents in the trough, a further shoreward translation of the current
distribution is necessary. This translation is difficult to accomplish, either
through manipulation of the roller parameters or by introducing additional
lateral mixing associated with wave breaking.
Roller diss. 0.1
Roller diss. 0.05
Distance Across Shore, m
Figure 44. Calculated (two different dissipation coefficients) and measured
longshore current for Kuriyama and Ozaki (1993) field experiment
(beach profile also shown for calculation domain)
Smith, Larson, and Kraus (1993) describe the Delilah field data
collection project, which was carried out during 1-9 October 1990 at Duck,
NC. During this cooperative experiment involving many institutions,
19 electromagnetic current meters and nine pressure gages were deployed in
water depths of 4 m to less than 1 m from 250 m offshore to the shoreline.
The instruments were arranged in a primary cross-shore array of co-located
pressure gages and current meters at nine locations and two secondary
longshore arrays of current meters. Waves and currents were measured along
the cross-shore array approximately every 3 hr. Smith, Larson, and Kraus
(1993) presented data measured on 14 October, and other cases from this data
set are employed here to test NMLong-CW. During that day, the beach
Chapter 6 Verification of Longshore Current Model