occurred during June through August, with higher heights and periods 

 occurring in September through Aprilo A north-to-south decrease in 

 height and period was also apparent for the three localities. The large 

 discrepancy between period observations, as measured by the gage and by 

 visual observers, might be due to a filtering effect caused by the shoal- 

 ing and breaking of incoming waves. Gage observations were made 800 feet 

 from the shoreline in an 18- foot water depth; visual observations were 

 made in the breaker zone. The longer period winter waves may reform 

 several shorter period secondary waves between the position of the gage 

 and the breaker zone. Shorter period summer waves appear to remain more 

 stable up to the breaker zone. Other explanations for the differences 

 between visual and gage period observations may be the sheltering of the 

 Boca Raton and Hollywood sites by the Bahama Banks, and the wider shelf 

 at and north of the Lake Worth gage, which takes its damping toll prefer- 

 entially on the long waves (R.G. Dean, CERB, personal communication, 

 1976). 



Using data from the Boca Raton site for the interval October 1969 to 

 March 1972, DeWall and Richter (1972) related the observed parameters of 

 wind velocity and direction to those of breaker height and direction 

 using the coastal sector method. This was done by deriving the ratio 

 of a measure of the southerly component of the longshore energy flux to 

 a measure of the total longshore energy flux (Fig. 31) . Winds directly 

 east or west and waves approaching normal to the shoreline were not com- 

 puted. The monthly averages of these directional ratios correlate well, 

 with a peak occurrence of northerly winds and waves in November and 

 southerly winds and waves in August. The data imply an abrupt change 

 in direction between the mean conditions in August (flow predominantly 

 from south to north) and September (flow losually from north to south) . 



4. Longshore Current Observations . 



Longshore currents, the littoral currents in the breaker zone moving 

 essentially parallel to the shore, are principally generated by waves 

 breaking at an angle to the shoreline. As indicated in the Shore Protec- 

 tion Manual (SPM) (U.S. Army, Corps of Engineers, Coastal Engineering 

 Research Center, 1975) , these currents are largely responsible for long- 

 shore sediment transport. 



Longshore current data are compiled in Figure 32. The monthly mean 

 current velocities (positive values equal flow from north to south) are 

 superimposed as circles on each histogram; monthly mean current speeds 

 (absolute values) as triangles (see App. B for definitions of these 

 terms, and a tabulation of the monthly and annual averages). 



The maximum observed longshore current velocity at each of the sites 

 was +4.28, +4.53, and -3.48 feet (+1.3, +1.38, and -1.06 meters) per 

 second at Jupiter, Boca Raton, and Hollywood, respectively. The average 

 current speed decreased north to south from highs of 0.9 3 foot (0.28 

 meter) per second at Jupiter, and 0.92 foot (0.28 meter) per second at 

 Boca Raton, to a low of 0.81 foot (0.25 meter) per second at Hollywood. 



49 



