7.331 Minikin Method: Breaking Wave Forces . Minikin (1955, 1963) 

 developed a design procedure based on observations of full-scale break- 

 waters and the results of Bagnold's study. Minikin's method can give 

 wave forces that are extremely high, as much as 15 to 18 times those 

 calculated for nonbreaking waves. Therefore, the following procedures 

 should be used with caution, and only until a more accurate method of 

 calculation is found o 



The maximum pressure assumed to act at the SWL is given by 



Hj, d^ 



p = 101 w (D + dJ, (7-76) 



^m Lq D ^ ^' ' 



where p^^ is the maximiom dynamic pressure, H^, is the breaker height, 

 dg is the depth at the toe of the wall, D is the depth one wavelength 

 in front of the wall, and Lp is the wavelength in water of depth D. 

 The distribution of dynamic pressure is shown in Figure 7-74. The 

 pressure decreases parabolically from p at the SWL to zero at a distance 

 of Ht/2 above and below the SWL. The force represented by the area under 

 the dynamic pressure distribution is 



(force resulting from dynamic component of pressure) (7-77) 



and the overturning moment about the toe is 



P.»H. d, 

 tn m s T 



(moment resulting from dynamic component of pressure) (7-78) 



The hydrostatic contribution to the force and overturning moment must be 

 added to the results obtained from Equations 7-77 and 7-78 to determine 

 total force and overturning moment. 



The Minikin formula was originally derived for composite breakwaters 

 comprised of a concrete superstnacture founded on a rubble substructure. 

 Strictly, D and L„ in Equation 7-76 are the depth and wavelength at the 

 toe of the substructure; d^ is the depth at the toe of the vertical wall 

 (i.e., the distance from the SWL down to the crest of the rubble substruc- 

 ture). For caisson and other vertical structures where no substructure is 

 present, the formula has been adapted by using the depth at the structure 

 toe as dgj D and L^ are the depth and wavelength a distance one wave- 

 length seaward of the structure. Consequently, the depth D can be found 

 from 



D = d + L. m, (7-79) 



7-146 



