distributed in deep water). Also, a large-scale current was specified with an
alongshore component growing exponentially from zero at the shoreline to
0.5 m/s in the offshore and having no component across shore (δ = 90 deg).
Standard (default) values were specified for the wave and longshore current
parameters: γ = 0.78, κ = 0.15, Γ = 0.4, Λ = 0.3, and cf = 0.003.
Figure 49 illustrates the simulated longshore current for waves and large-
scale (L-S) current together, as well as for waves only. Also, the cross-shore
distribution of the input longshore current is shown. In the absence of waves,
NMLong-CW will exactly reproduce the input longshore current (see
and the simulated current will typically also differ from the large-scale
longshore current outside the region of wave-generated currents. Because the
influence of the waves disappears in deeper water, the simulated current will
approach the input external longshore current (if there is no wind-induced
current).
1.2
Waves and LS current
Waves only
Large-scale (LS) current
0.8
0.4
0.0
0
200
400
600
800
1000
Distance Across Shore, m
Figure 49. Results of simulating large-scale current on wave-generated
nearshore current
Concluding Remarks
The capability of NMLong-CW to predict the cross-shore distribution of
the longshore current was evaluated by comparison with several high-quality
laboratory and field data sets. This comparison also involved the mean water
level and the wave height, if these quantities were recorded. The data
encompassed a wide range of forcing conditions involving both
monochromatic and random waves. Furthermore, different beach profile
shapes were investigated, as well as varying bottom roughness.
NMLong-CW gave good agreement with measurements for cases where
the profile was monotonically increasing with distance offshore, provided
that the roller model was included. Simulations without the roller model
69
Chapter 6 Verification of Longshore Current Model
Previous Page
