For comparison the numerical example carried out in Section III 

 is seen to correspond to an incident wave amplitude between the 

 incident wave amplitudes of Run Numbers 470 and 469 in Table 6. 



b. Determination of the Internal Energy Dissipation . Having 

 determined the energy dissipation on the seaward slope, the next step 

 is to determine the internal energy dissipation. To perform this 

 analysis one must first determine the characteristics of the rectangular 

 breakwater which is hydraulically equivalent to the trapezoidal, 

 multilayered breakwater shown in Figure 25. As an example of the 

 computations involved, the homogeneous rectangular breakwater which is 

 hydraulically equivalent to the breakwater configuration shown in 

 Figure 25 was determined in Section IV. 2. Thus, the equivalent 

 rectangular breakwater has the characteristics obtained in Section IV. 2, 

 i.e.. 



Stone size = d = 0.0625 foot ; Porosity = n = 0.435 , (167) 

 and a width I given by equation (163) 



AH 



i = 2.52 — T^ feet , (168) 



e AH^ 



in which AHg and AH-p are the runup on the equivalent rectangular and 

 on the trapezoidal breakwater, given by equations (159) and (160), 

 respectively. 



As discussed in Section IV. 2, the determination of £g from 

 equation (168) involves a tedious iterative procedure. A fairly good 

 first guess for the value of the reflection coefficient, Rj , involved 

 in determining the ratio AHg/AH-p from equation (161) may, however, be 

 obtained by taking AHg/AH-p equal to unity. Hence, a preliminary 

 solution is obtained by taking 



£ = 2.52 feet . (169) 



The equivalent rectangular breakwater characteristics are therefore 

 given by equations (167) and (169). The incident wave characteristics 

 are given by equation (164) with an equivalent incident wave amplitude, 

 aj, given by equation (146). The computations involved in determining 

 the partition of the energy associated with the equivalent incident 

 wave among reflected, transmitted, and internally dissipated energy is 

 therefore carried out according to the procedure developed in Section II 

 of this report. In Section II, the details of this computation were 

 presented in the form of a numerical example. By inspection of the 

 incident wave and breakwater characteristics used in the numerical 

 example in Section II, these characteristics for the Froude model listed 



92 



