p 



c. Calculation of is Using LEO Data . An alternative method of 

 calculating the energy flux factor P is to use data from the CERC Littoral 



Environmental Observation (LEO) field data collection program. LEO data 

 include visual observations of nearshore wave heights and periods and long- 

 shore current velocities. The program is discussed by Berg (1968), Szuwalski 

 (1970), Bruno and Hiipakka (1974), Balsillie (1975), and Schneider (1981). 

 Use of LEO data permits replacing the hard-to-measure wave angle term in 

 equation (4-40) with LEO longshore current measurements. The current measure- 

 ment is made by timing the travel of a dye patch in the surf zone. 



The equations and example problem which follow are taken from Walton 

 (1980), which presents derivations and additional references. 



The equation giving the longshore energy flux factor with LEO data 

 variables is 



P. = ./. .„ ^ ^ (4-51) 



'' (r)(f^ 



'°^LH 



where 



and 



LH 



p = fluid density 



g = acceleration of gravity 



H , = breaking wave height 



so 



W = width of surf zone 



V = average longshore current due to breaking waves 



C. = friction factor (assume 0.01) 



X = distance to dye patch from shoreline 



(V/Vo),„ is the dimensionless longshore current based on Longuet-Higgins 

 (1970ay. It is assumed that the LEO breaking wave height is a good approxi- 

 mation of the significant breaking wave height and that the mixing parameter 

 in Longuet-Higgins' theory is 0.4. 



*************** EXAMPLE PROBLEM 4*************** 



GIVEN ; A LEO observation with the following estimated values of wave height, 

 longshore current velocity, width of surf zone, and distance of dye patch 

 from the shoreline 



4- 100 



