Figure 3-16 shows a large positive area within the rip neck, which means the depth-
integrated, time-averaged continuity equation, shown in Equation 3-5, is not satisfied.
Therefore, more fluid is apparently exiting than entering the computational bins located
in the rip neck. In actuality, mass is being conserved throughout the visible domain
because the still water level (SWL) remains constant. This discrepancy in the
conservation of mass flux may have resulted from assuming depth uniform flow and the
effects of Stokes drift. Stokes drift due to incident waves has the largest effect on rip
current flow by impeding the offshore directed neck, which is where the continuity
equation is not satisfied. For future research, wave heights could be determined from a
wave model, such as REF/DIF, to calculate a value for Stokes drift throughout the visible
domain. Test 16 produced the least favorable results from the long test category.
Velocity Distribution
Probability density functions (PDFs) were created for each of the long tests in order
to analyze the distribution of the longshore and cross shore components of velocity at
four locations in the visible domain. The four computational domains throughout the rip
system used to obtain the PDFs are shown in Figure 3-17. Figure 3-18 shows the plot-
type described above for test 16. Appendix I contains this same plot-type for every long
test. The mean and standard deviation of the velocity distribution for the components (u,
v) can be seen in these PDF figures at the four specified locations. The number of
velocity measurements used to create the PDFs is also noted in the figures. Equation 3-5
was used to calculate the standard deviation of the velocity component distributions.
S= (X, X)2 (3-5)