is a function of the reflection coefficient, R^ , of the equivalent 

 breakwater. Since this reflection coefficient cannot be determined 

 until the width of the equivalent breakwater, i^ , is known one is 

 faced with a tedious iterative procedure. However, in most cases a 

 sufficiently accurate estimate of Rj may be obtained by assuming 

 initially that AHg/AH-p is unity and use this estimate along with the 

 best estimate of R to obtain a new value of AHg/AHj from equation C161). 



Numerical Example of the Determination of the Equivalent 

 Rectangular Breakwater . To illustrate the procedure for the 

 determination of the equivalent rectangular breakwater the trapezoidal, 

 multilayered breakwater configuration tested experimentally by Sollitt 

 and Cross (1972) and shown in Figure 25 is considered. The breakwater 

 is divided into five horizontal slices, I-V (Fig. 25), and the 

 reference material is chosen as the material with stone size ^2 = 0.75 

 inch (1.9 centimeters]. Since the porosities of the three porous 

 materials were reported to be essentially equal by Sollitt and Cross 

 (1972) , the porosity of all materials as well as the reference material 

 is assumed to be 0.435. This in turn means that the ratio of the 

 hydraulic characteristics of the various porous materials, 6j^, according 

 to equation (52) with Bq = 2.7 reduces to the inverse of the ratios of 

 the stone sizes, i.e., 



^1 ^2 ^3 ^2 



r = ^= '^•^ ' r= d^= 2-° • ^1^2) 



^2 1 ^2 3 



From the geometry of the breakwater shown in Figure 25, with the 

 top layer of cover stones removed, the equivalent breakwater width is 

 readily calculated as shown in Table 5. 



Introducing the numerical result obtained in Table 5 in equation 



(158) , the equivalent breakwater width, I , is obtained as 



e 



_ AH AH 



I = (0.1819) jrf- inches = 2.52 — ^ feet . (163) 



Thus, the homogeneous rectangular breakwater which is hydraulically 

 equivalent to the trapezoidal, multilayered breakwater (Fig. 25) 

 consists of material of stone size d = d2 = 0.0625 foot (1.9 centimeters) 

 and porosity n = 0.435. The equivalent width, £g, is given by equation 

 (163) and a first approximation may be obtained by taking AHg/AHj = 1, 

 i.e., £,g = 2.52 feet (0.77 centimeter). 



It should be noted that the homogeneous rectangular breakwater 

 assumed in the numerical example presented in Section II, Table 1, has 

 the characteristics of the hydraulically equivalent breakwater given 



87 



