misleading in the surf zone when winds blow overland from the shore, and 

 shallow depths allow bottom boundary layers to interact with wave breaking 

 turbulence at the surface. 



The importance of winds was mentioned by Shepard and Inman (1950) . 

 Field experimenters, however, find it difficult to differentiate effects 

 of wind shear from short-period wind waves and the currents they generate, 

 Linear multiregression analysis has been attempted to separate the 

 relative importance of independent variables to generate the longshore 

 current. Harrison and Krumbein (1964) found windspeed to rank ahead of 

 offshore wave direction. If breaker angle was used instead, the result 

 would be reversed which points out difficulties with regression studies 

 if the wrong variables are employed. Sonu, McCloy, and McArthur (1967) 

 found wind to be the second most important field variable influencing 

 longshore current. Field tests of wind data should be recorded if com- 

 parisons are to be made. A recent study by Nummedal and Finley (1978) 

 evaluated whether or not the inclusion of additional physical parameters 

 (other than wave field characteristics) could significantly improve 

 current predictions. More than 250 observations were made over 1 year at 

 Debidue Island beach. South Carolina, using the Littoral Environmental 

 Observation (LEO) program. Four, widely varied equations for longshore 

 current prediction were used to evaluate the linear combinations of wave 

 and other physical parameters, including the longshore component of wind 

 velocity. It was invariably found that this wind component explained 

 most of the observed variance in the current velocity. Consequently, 

 their statistical data analysis suggested that wind stress is an impor- 

 tant factor in longshore current generation. 



Further strong evidence supporting this conclusion came when Dette 

 and Fuhrboter (1974), in their North Sea experiments using EM current 

 meters located at middepths, concluded that high longshore current 

 velocities (up to 1.5 meters per second, means) could be expected during 

 two different weather patterns: 



(1) Heavy storms with high breakers (>3 meters) and small wave 

 breaking angles (<25°). 



(2) Winds blowing parallel to shore with low breakers (<1 meter) 

 but large breaking angles (>25°). 



When the wind blew parallel to the shoreline and shifted from south to 

 north, the mean longshore current changed almost at the same time to 

 create mean currents in opposite directions of more than 1 meter per 

 second. Between these patterns winds blew from land to sea, small waves 

 were present and longshore currents were near zero. Windspeeds were 5 

 to 10 meters per second. 



Fox and Davis (1971, 1976) included the barometric pressure which 

 causes the winds in their empirical analysis. They directly related 

 local time variations (days) of barometric pressure to a longshore 

 current velocity which varied in time (days) as well. The correlations 



44 



