2. LEO Data Collection and Analysis . 



Figure 6 shows three sites where twice daily surf data were collected using 

 procedures developed under the CERC LEO program (Bruno and Hiipakka, 1973; Berg, 

 1968). These data include observations of surf conditions, local winds, and 

 littoral currents. The primary concern of this study was the estimates of 

 breaker height, breaker direction, and longshore current. To aid in estimating 

 the breaker direction, LEO observers were provided with a protractor on the 

 data form. Longshore currents were measured using small packets of dye which 

 disperse upon injection in the surf zone. The observers measure the distance 

 the dye travels parallel to the shoreline. Current speed is estimated from the 

 movement of the dye patch centroid over a 1-minute period, and current direc- 

 tion is noted. Surf zone current velocities are not uniform; therefore, the 

 width of the surf zone is estimated as well as the distance from the shoreline 

 to the point of dye injection. 



LEO data were used to compute the longshore energy flux factor, using two 

 methods of computation, in order to relate the wave energy to the longshore 

 sediment transport. The first method involved the typical approach to computing 

 the longshore energy flux, using wave heights and wave angles at breaking. This 

 method utilizes the SPM equation (4-29) : 



^Is = ^1^ C sin 2ab (5) 



where 



P£s = longshore energy flux factor 



p = fluid density 



H, = breaking wave height 



a, = breaking wave angle 



C = group wave velocity at breaking. 



Using linear wave theory, shallow-water assumption and a linear relationship 

 between breaking wave heights and depth equal to 



Hb (6) 



^b 



where dj^ = breaking wave depth, equation (5) becomes 



5/2 /p\l/2 



- PR ,, 



- 16 "b 



(f) sin 2ab (7) 



The longshore energy flux computed from equation (7) is dependent on only two 

 surf zone parameters — breaking wave height and breaking wave angle. The 

 assumed value of k for computation, k = 0.78, is reasonable for various mono- 

 chromatic wave theories (e.g., see Longuet-Higgins , 1970). The breaking wave 

 height measured by LEO observers is assumed to be the significant wave height 



24 



