88
Figure 5.20: Rip-current velocities adjacent to the down wave side of the jetty. Comparison
of experimental and numerical results.
of .139 ft. One would expect the depth averaged velocity to be somewhere between the
mid-depth velocity and the bottom velocity. The model appears to slightly underpredict
the rip current. In figure 5.19 a circulation cell in the lee of the groin is barely discernable.
In figure 5.21 the circulation cell is very obvious.
5.5 Shore Parallel Emerged Breakwater
In order to solve for the wave and current field resulting from the interaction of waves
and an emerged breakwater several boundary conditions at the breakwater are incorporated
into the model in addition to the boundary conditions already discussed in sections 4.3
and 4.4. The breakwater is represented as being infinitesimally thin and impermeable.
Figure 5.22 shows the position of the breakwater on the shoreward side of the I = Ibrk grid
row. The impermeability condition implies that neither waves nor currents pass through
the breakwater. The no current condition is easily imposed in the circulation model by
making Cf(lBjyr+i> J) equal to zero for the entire length of the breakwater. In addition the
circulation model is modified so that momentum diffusion and derivatives do not take place