Monthly mean net current velocities correlated reasonably well with 

 monthly mean breaker directions (Fig. 33). During those months when 

 breakers were approaching from the south of shore-normal, longshore cur- 

 rents generally flowed to the north. During the months when breakers 

 were approaching from the north of shore-normal, longshore currents gen- 

 erally flowed to the south. As the breaker approach angle increased, so 

 did the average current speed. 



5. Longshore Transport . 



Longshore transport rates have been estimated for the southeast coast 

 of Florida and are listed in Table 3. U.S. Army, Corps of Engineers (1971) 

 summarized estimates of the net transport rate based on impoundment rates 

 and dredging records. Walton's (1973) estimates of net and gross long- 

 shore transport rates in the study area were based on shipboard observa- 

 tions. However, Walton questioned the validity of his estimates south of 

 Ji^iter Inlet due to possible effects of the Florida Current and the 

 Bahama Banks. All estimates have confirmed a net north- to-south trans- 

 port direction. Specific field indications of transport direction toward 

 the south include the deposition north and erosion south of: (a) South 

 Lake Worth jetties, (b) Boca Raton jetties, (c) Hillsboro Inlet jetties, 

 (d) Port Everglades jetties, (e) Bakers Haulover jetties, (f) groin at 

 Hollywood-Hallendale City line, and (g) seawall and groins at Parker 

 Dorado condominium at Hallendale-Golden Beach City line (R.G. Dean, 

 personal communication, 1976). The estimated magnitude of the net long- 

 shore transport rates as summarized by the U.S. Army, Corps of Engineers 

 (1971) is observed to decrease southward between Jupiter and Hollywood. 



Using the breaker height and direction data collected during this 

 study, independent longshore transport rates were calculated and are 

 listed in the last three columns in Table 3. The gross transport rate 

 values from Galvin (1972) were computed by doubling the square of the 

 mean yearly breaker height. Values from Das (1972) were computed based 

 on individual observations of breaker height and direction. The SPM 

 values were computed using the joint frequency distribution of the height 

 and direction, following the example of the "wave energy flux method" on 

 page 4-102 of the Shore Protection Manual (U.S. Army, Corps of Engineers, 

 Coastal Engineering Research Center, 1975). 



It should be noted that the calculated results in Table 3 are only 

 potential values, based on available wave energy. Other factors, such 

 as limits on the sand supply and protection afforded by the coquina ledge, 

 would be expected to reduce the actual longshore transport rate. 



Estimates of gross transport rates using data from this study confirm 

 a trend of decreasing magnitude from north to south. However, the compu- 

 tation of net transport rates (Das, 1972; SPM) results in an apparently 

 anomalous reversal of direction at Boca Raton and Hollywood. The Holly- 

 wood reversal is most likely the result of wave refraction at the deep 

 entrance channel at Port Everglades, but may also be the result of the 

 relatively calm weather which prevailed during the study period. 



53 



