(1) Determine the breakwater cross -sectional geometry and material 

 characteristics of diameter and porosity. 



(2) Estimate the energy dissipation on the seaward face of the breakwater 

 assuming it is rough and impermeable. This is done by solving Madsen and 

 White's equation (127) implicitly using their Figures 15, 16, and 17 and 

 applying a correction factor from their Table 2. 



(3) Assume as a first approximation that the head across the breakwater 

 is equal to runup determined from step 2 above. 



(4) Transform the trapezoidal breakwater into a hydraulically equivalent 

 rectangular breakwater (see Sec. 4.2 of Madsen and White). 



(5) Estimate the coefficient of transmission through the structure, Ky^, 

 using Madsen and White's Figures 2 and 3 and implicitly solving their equation 

 (57). 



(6) Obtain a revised estimate of the head across the breakwater using 

 Madsen and White's equation (161). (Repeat steps 4, 5, and 6 until a con- 

 verged solution is obtained.) 



(7) Estimate wave runup on the breakwater using the method of Ahrens and 

 McCartney (1975) and the coefficients given in Table 3 of this study. 



(8) Calculate the transmission by overtopping coefficient, Ky^ , using 

 equations (14) and (15) in this study. 



(9) Calculate the transmission coefficient, Ky, using Ky^ from step 5 

 and Y^rpQ from step 8 and 



Ky = ' Kyt "*" ^To 



Madsen and White compared the model predictions to physical model results 

 from Keulegan (1973) for rectangular breakwaters composed of one rock type, and 

 from Sollitt and Cross (1976) for a multilayered trapezoidal breakwater made 

 of riprap. There was good agreement between analytical and physical model 

 results for predicting the wave transmission coefficient for long nonbreaking 

 waves. However, the following questions need to be answered to determine the 

 range of usefulness of the Madsen and White model: 



(1) How useful is the model for predicting transmission coefficients 

 for relatively short waves? 



(2) Can the model be used if waves are breaking? 



(3) Can the model be used for breakwaters with concrete armor units? 



(4) Can the model be used for irregular waves? 



(5) How sensitive is the model to porosity of the materials? 

 (Porosity is an input parameter and although it probably does not vary 

 over a very wide range, its value will probably not be known accurately 

 in a design situation.) 



43 



