Changes in the MSL shoreline have been calculated as discussed in Section 
3, and are graphed for each profile line in Appendix B. This parameter is 
sometimes invoked as an indicator of seasonal beach changes and, indeed, may 
show persistent long-term trends. Short-term changes in MSL intercept may 
also be caused by migrating rhythmic topographic features, such as cusps or 
rip channels, and may be incorrectly interpreted unless closely spaced profile 
lines are obtained. 
The major disadvantage of the eigenfunction technique is that the results 
may be more obscure than simple volume calculations or MSL intercept plots. 
Beach changes may be regular and predictable, but the eigenfunctions do not 
always have simple physical interpretations. In much work to date on west 
coast beaches, the eigenfunctions have had physical analogues (e.g., Winant, 
Inman, and Nordstrom, 1975; Winant and Aubrey, 1976; Aubrey, 1979). Eigen- 
function analyses on other beaches have shown similar characteristic shapes. 
The alongshore variability of the beach profile measurements has been in- 
vestigated by plotting the mean square value (MSV) and variance (VAR) of each 
line 1 through 21. No consistent trends emerged from this analysis except for 
the plot of total VAR of the demeaned data (Fig. 22).. Though the conclusion 
Must remain tentative, since each profile line did not contain the same number 
of points nor extend the same distance offshore, there is a trend of increas- 
ing variability from north to south along the island. The reason for the 
greater variability (if it is real) may be associated with more active trans- 
port processes occurring along the unstructured Beach Haven Inlet. 
The alongshore variation was also examined to see if differences existed 
between profiles relatively evenly spaced between groins (profile lines 5, 7, 
9, 12, 13, 14, 16, 20) and those closely adjacent to groins (profile lines 4, 
6, 8, 10, 11, 15, 17, 18). No marked difference was discernible from these data. 
The eigenfunction analysis did not differentiate between beach responses to 
structural control simply on the basis of gross characteristics such as MSV, 
VAR, and percentage of VAR accounted for by the first eigenfunction. Exami- 
nation of the closely spaced profile lines within the groin field (profile 
lines 22 to 30) will be discussed later in this report. 
The demeaned spatial profiles demonstrate two major relationships between 
the first and second eigenfunctions (Fig. 23,a). The first group of profile 
lines (1, 2, 4, 5, 6, 10, 11, 12, 14 to 17, 19, 20) is the dominant form and 
has the second eigenfunction in phase spatially with the first on the beach 
backshore, and out of phase in the foreshore. For a positive temporal second 
eigenfunction Lense); the second eigenfunction shows an enhanced buildup in 
the backshore and a reduced buildup in the foreshore. For a negative weight-— 
ing for cy (t), the backshore erodes while the foreshore accretes. Since the 
second eigenfunction is always less dominant than the first, this effect is 
second order. 
The second profile grouping (profile lines 7, 8, 9, 13, 18) is shown in 
Figure 23(b). The first eigenfunction has a spatial sign difference between 
the foreshore and backshore, while the second eigenfunction has no sign dif- 
ference. This eigenfunction representation shows the same result as the pre- 
vious grouping; a positive weighting on the second function, c,(t), indicates 
accretion on the backshore and erosion on the foreshore, while a negative cy (t) 
48 
