J 
The high variability in the MSL position and sand volume may also be related 
to the position of the profile lines relative to offshore features, such as 
sandbars and the shoreface-connected shoals. The wave refraction diagrams 
(Figs. 11 to 16) show that the shoals refract simple waves approaching from, 
for instance, the northeast in complicated ways. Measurements of flow over 
the shoals and the longshore variation in wave characteristics may be neces- 
sary to adequately resolve this question. 
The available data were evaluated to determine the direction and rate of 
net longshore transport. Neither can be determined with certainty using these 
data, but strong arguments can be made for a net southerly transport, at least 
south of profile line 24. Most severe storms arrive from the east or northeast, 
generating longshore currents and oblique waves which transport material from 
north to south. Clear evidence of this exists in the single year study of 
the closely spaced profile lines. The unfortunate locations of other single 
profile lines make direct confirmation of this phenomenon from profile line 
evidence impossible. Reversals in transport direction have been shown to 
exist, and evidence of a possible node in the transport is shown along closely 
spaced profile lines 22, 23, and 24. 
Calculations of the rate of littoral transport are based upon a linear 
relationship between the volume transport rate and the longshore component 
of wave energy flux evaluated at the breaker zone, Po,, (U.S. Army, Corps of 
Engineers, Coastal Engineering Research Center, 1977). ‘lhe shallow-water break- 
ing criterion and solitary wave theory can be used to show that Py). is quite 
sensitive to wave height and breaker angle. Relatively small errors in these 
values cause large errors in Pgg. Visual estimates of breaker conditions, 
available for part of the study, indicated a predominance of normal wave inci- 
dence with this zone defined as waves approaching from directly offshore to 
5° on either side. Transport may, therefore, have been in either direc- 
tion. The transport rate relationship to energy flux is based upon field 
measurements on plane, unstructured beaches and does not account for effects 
of groins, inlets, tidal currents or offshore topography. The uncertainty 
caused by these factors makes quantitative estimates of the transport rate 
meaningless. 
Bo. Cabyalil Engineering Implications. 
The Long Beach Island beaches were identified as experiencing "critical 
erosion" (U.S. Army Engineer Division, North Atlantic, 1971). The rate of 
erosion and reason for this designation, however, were not specified. Evalu- 
ation of these BEP data indicates that the beaches are accreting or remaining 
stable at several locations and in spite of an expected erosion trend induced 
by sea level rise. Several of the profile lines show a marked increase in 
sand volume after groin construction began in 1964. Profile lines 14, 16, 
and 17 increased in sand volume and have remained relatively constant since 
about 1968 (App. D). Whether this trend is a result of groin construction 
or a natural beach cycle is unknown. Profile line 21 at the south end of Long 
Beach Island is near the last structure before the wildlife refuge and has 
shown a marked erosion trend over the course of the study which may be related 
to the sand trapping by the groins to the north. This conclusion ‘must remain 
tentative since no profile data are available prior to the BEP. 
56 
