b. Long-Term Changes . All four profile lines depict cyclic changes, 

 with a slight net gain in shoreline position and beach voliome (Figs. 43 

 and 44) . Similar trends of gains and losses were observed on each of 

 the four profile lines. Changes on profile lines III and IV most closely 

 paralled each other; changes on profile lines I and II, the most widely 

 spaced lines, were the most dissimilar of changes on adjacent profile 

 lines. Profile line I underwent a significant departure from the trend 

 of the three profile lines to the south by gaining sand at a rapid rate 

 during the last quarter of 1969 and again in 1970. The 1969 gain appear- 

 ed to be coincident with the excavation work at the condominium site 

 immediately to the north (Fig. 6) . Evidence of a southerly-migrating 

 sand hump following the dune-leveling operation, such as reported at 

 beach- fill sites elsewhere (Everts, DeWall, and Czemiak, 1974), is not 

 apparent from the subsequent changes on profile lines II, III, and IV. 

 Similar erosional and accretional trends are reflected by the computed 

 volume changes and shoreline position changes at each of the four profiles. 



The changes at Boca Raton appear to be seasonal, but do not show the 

 same pattern as changes observed at Jupiter. The beach tends to be wider, 

 with a maximum sand volume above MSL during the winter months, while the 

 maximum loss rates occur during the summer months. Monthly averages of 

 the shoreline position and sand volume on the four profiles fur an average 

 year are plotted in Figures 45 and 46. Maximum beach width and volume 

 occur in February and again in June. Minimum beach width occurs in August; 

 the minimum beach volume in October. 



D.W. Kirtley, Fort Pierce, Florida (personal communication, 1973), 

 suggested that the encrusting worm reefs, which commonly occur on the 

 beach-rock ledge at Boca Raton, may be responsible for the anomalous 

 accretion at the site. The worm reefs thrive, in the surf zone, and have 

 been observed to build their reefs upward by accumulating sand at rates 

 of up to 2 centimeters per day in the laboratory. Although the worm-built 

 structures probably cannot withstand the forces of storm waves and the 

 worms themselves cannot withstand extended burial, they must have an 

 effect on the littoral processes and sand storage rates at Boca Raton. 



c. Nearshore Profile Changes . In October 1969 the Boca Raton profile 

 lines were extended seaward from the beach-rock ledge to a distance of 540 

 feet (165 meters) from the MSL shoreline and an average maximum depth of 

 14 feet. A total of 262 nearshore profile surveys was made along each of 

 the four profiles at an average of once each 4.5 days. No nearshore sur- 

 veys were made from July through December 1972. Nearshore surveys were 

 dependent on conditions favorable for safe scuba diving. Unfavorable 

 diving conditions were generally caused by high breakers (4 feet or more) 

 with resulting high current velocities. Other contributing problems in- 

 cluded poor visibility, debris, insufficient air to complete a survey, 

 equipment malfimction, and hazardous marine life. 



Seaward of the beach-rock ridge, the nearshore zone consisted of one 

 or more longshore bars. These bars were continually shifting in an 



70 



