L. = 5 . 12 Tt 



(52) 

 = 250.88 ft 



so that H /gT 2 = 0.0038. From the SPM (1984) 



H b /H =1.28 

 so that H b - 7.68 ft and 



H b /gT 2 = 0.00487 

 Also from the SPM 



H b /h b = 1.0 

 so that h b = 7.68 ft. 



Since the beach slope is 0.05, the distance from the pre-seawall msl/beach 

 profile intersection to the point of wave breaking can be obtained by dividing 

 the depth of breaking by the slope: 



X b = h b /0.05 - 153.6 ft 



By a similar method, the distance of the seawall location from the point of 

 wave breaking can be obtained as follows: 



The distance of the seawall from the msl/beach profile intersection is 

 found by dividing the depth at the toe of the wall by the beach slope: 



= 2.0 ft/0.05 = 40.0 ft 

 Now, 



X = X b - 40.0 = 153.6 - 40.0 = 113.6 ft 

 Therefore, 



X s = 113.6/153.6 = 0.74. 

 Substituting into Equation 56 yields 



-jJP = 1.60 (1 - 0.74) 2/s 

 "b 



= 0.93 



so that the maximum scoured depth is S max =0.93 (H b ) = 7.1 ft . 



39. Using small-scale two-dimensional laboratory studies, Song and 

 Schiller (1973) produced a regression model that predicts relative ultimate 

 scour depth expressed as S max /H . The relative ultimate scour was given as a 



39 



