volumetric gain of 15.3 cubic yards per foot (38.4 cubic meters per 

 meter) . Unusual conditions are not reflected in the LEO data for these 

 two surveys, although the weather system could have been under the in- 

 fluence of Tropical Storm Agnes which was developing off the Yucatan 

 coast on 14 and 15 June. 



b. Long-Term Changes . Figures 39 and 40 are plots of the average 

 monthly MSL shoreline position and volume for the two Jupiter profile 

 lines, referenced to the shoreline position and beach volume at the first 

 survey (see also Apps. F and G) . The plotted regression line is a least 

 squares fit for the beach changes from January 1969 through December 1972. 



The zero MSL position in Figure 39 is the value of the MSL position 

 at the first survey in January 1969; the starting point for the profile 

 line I curve for the MSL position is a negative value, reflecting an 

 average MSL position in January 1969 that was slightly landward of the 

 MSL position on the first surveyed profile during January 1969. The 

 straight line (-0.4 foot (-0.12 meter) per year) is a least squares fit 

 to the average of the monthly values of MSL at the two profiles, using 

 the months from January 1969 through December 1972. The partial year of 

 data collected after December 1972 was not included in the least squares 

 analyses because it was not a complete annual cycle. 



The unit volume data are shown in similar fashion in Figure 40. The 

 zero volume in the volume of the first survey, and the straight line 

 (-0.71 cubic yard per foot (-1.8 cubic meters per meter) per year) is a 

 least squares fit to the 4 years of average monthly averages (January 

 1969 through December 1972). The MSL position and unit volume were 

 previously defined in Figures 20, 21, and 22, The same format used in 

 Figures 39 and 40 is also used for comparable data at Boca Raton and 

 Hollywood. 



The monthly MSL and volume changes both indicate cyclic changes at 

 Jupiter, with a slight net loss in both the shoreline position and beach 

 volume above MSL. There is good correlation between the changes observed 

 on the two profile lines, which is expected with a spacing of only 250 

 feet. However, the magnitude of changes on profile line II is greater 

 than on profile line I, suggesting some variation in the attitude of the 

 underlying coquina limestone. There is also a good agreement between 

 the two parameters analyzed; i.e., a gain or loss in sand volume is asso- 

 ciated with a concurrent gain or loss in the position of the MSL shoreline. 



The cyclic changes are seasonal and may be a result of the onshore- 

 offshore sediment transport which has been documented elsewhere by other 

 investigators (e.g.. King, 1959; Shepard, 1963; Bascom, 1964). During 

 the summer months the longer, lower waves transport sand onto the beach, 

 causing a seaward translation of the shoreline and an increase in the 

 total sand volume on the beach. Another possible explanation for the 

 cyclic changes might be the influence of the coquina exposures to the 

 north, damming up littoral drift being transported to the north during 

 the summer months. 



64 



