At profile line 18, pipes 1, 2, and 3 were read on both 25 November 
and 19 December 1970. Maximum erosion at any one of the pipes was 0.5 
foot, measured at pipe 4 where the sand level changed from 2.5 to 2.0 feet 
MSL. There was no accretion at any of the pipes. 
VI. DISCUSSION 
Changes in the MSL contour position and unit volume were tabulated 
for each locality and summarized in Figures 23 and 24. For 78 of the 91 
profile lines surveyed, both prestorm and poststorm surveys reached the 
MSL contour. The MSL change and the volume changes at each of these 78 
PRotieke linesmare plotteds inh egune 25... /Oniy S7iof the) 7/S8plotteds pro 
files show like changes in sign; i.e., volume increases when shoreline 
accretes or volume decreases when shoreline retreats, although it is 
often assumed that the two parameters (volume change and shoreline posi- 
tion change) are equally good indicators of erosion or accretion. 
Of the 21 profile lines showing a negative correlation between volume 
change and MSL contour change (one increases when the other decreases) , 
all but 2 lost volume and accreted at the shoreline (Fig. 25). A good 
example of the negative relation between changes in MSL and unit volume 
can be seen on Cape Cod profile line 01 (Fig. 10). The prestorm MSL 
contour intercept. occurs at +4.8 feet. The poststorm survey indicates 
erosion on the upper profile and accretion on the lower end of the pro- 
file as a bar. The crest of the poststorm bar was about 1.5 feet above 
the MSL contour, which resulted in triple intercepts of the MSL contour 
with the profile at -51.0, +21.2, and +91.5 feet. Thus, the most seaward 
shoreline shifted 86.7 feet seaward; the volume at the profile was actually 
reduced by 65.0 cubic yards per foot between MSL and +52 feet. 
The only two profile lines to show a net increase in unit volume with 
a net retreat in shoreline were Jones Beach profile line 08 and Long Beach 
Island profile line 04. 
For the 17 December 1970 storm, it can be concluded that a shift in 
the MSL contour is generally proportional to unit volume changes on the 
profile above MSL. Usually, a retreat in the MSL contour is accompanied 
by a unit volume loss from the beach profile above MSL, but in a signif- 
icant number of cases, a decrease in unit volume is not accompanied by a 
retreat in the MSL shoreline. 
The dashline in Figure 25 shows the rule of thumb relating permanent 
volume loss to permanent shoreline shift (1 cubic yard per foot for a 
1-foot shoreline change, U.S. Army, Corps of Engineers, Coastal Engineer- 
ing Research Center, 1975, Vol. 1, p. 4-122). The nonpermanent storm 
loss from above MSL is apparently much less than the rule of thumb. 
Storm Surge Elevation and Duration versus Maximum Erosion Elevation. 
Maximum water elevations, maximum observed wave heights, and contours 
of maximum erosion for each locality surveyed are summarized in Table 10. 
73 
