indicates erosion on the backshore and accretion on the foreshore. The primary 
difference in the two eigenfunction representations is the negative covariance 
between the foreshore and backshore in the first eigenfunction for the second 
grouping and positive covariance for the first set of profiles. No physical 
explanation for the different beach response for these two groupings is 
apparent. 
For the mean beach eigenfunction (those with the mean profile retained), 
the first eigenfunction is analogous to a mean beach profile. There is con- 
siderable variation in the beach slopes for the different profiles, but the 
eigenfunction analysis shows no systematic relationship between these pro- 
file slopes and proximity to beach structures. 
3. Groin Field Studies. 
Closely spaced profiles were taken along a section of beach protected by 
evenly spaced groins between the towns of Loveladies and Harvey Cedars (profile 
lines 22 to 30). Ten surveys of each profile line were made over a period of 
nearly 1 year (28 Aug. 1972 to 11 June 1973). Each set of parallel profile 
lines, three within each groin compartment, was arranged with the center profiles 
(23, 26, 29) spaced equally between the groins and the other lines two-thirds 
of the remaining distance to the groin on either side. Changes, between surveys, 
in MSL position and sand volume at each profile line have been prepared in 
Appendixes B and D, respectively. The changes within the groin field between 
survey dates are shown in Figure 24 for MSL position and Figure 25 for above 
MSL sand volume. Comparison of Figures 24 and 25 shows that the above MSL 
volume change is highly correlated with the MSL position change. 
Visual wave observations were made once each day in the vicinity of Harvey 
Cedars during much of the period of these surveys. These data are not suitable 
for quantitative determinations of transport rate and direction because direc- 
tion estimates are imprecise and data are not complete. The visual data were 
reviewed, however, for qualitative estimates of transport during each measure- 
ment interval. 
a. 29 Aug. - 16 Oct. 1972. Few visual wave observations were taken during 
this interval and none are available after 21 September. It is obvious, how- 
ever, that each groin cell responded similarly to processes occurring before 
the 16 October survey. The north side of each groin cell (A, B, C in Figs. 24 
and 25 ) shows general erosion while the south side shows accretion, indicating 
longshore transport from north to south. The net gain in above MSL sand volume 
in each groin cell indicates that sand must have been contributed to the groin 
field from offshore or updrift. Tropical storm Carrie occurred shortly after 
29 August, but its influence on the measured beach changes is unknown. 
b. 16 Oct. - 4 Dec. 1972. The pattern of change in above MSL volume and 
MSL position reversed in all groin cells during this interval. Erosion occurred 
at the south end of each cell with accretion at the north end. No storms are 
recorded during the interval (Table 2) but visual wave observations are avail- 
able for 30 of the 49 days. Most of these record waves approaching from directly 
offshore. Two days prior to the survey, however, waves were observed breaking 
at an angle from 5° to 30° to the shoreline, approaching from the south. These 
would have induced northward transport and may be responsible for the observed 
pattern of change. 
50 
