It IS seen 



AH^ = E(AH^) , (153) 



n 



in which AH is the head loss associated with the segment of length, I 

 and hydraulic characteristics, 3 . From equation (151) it is seen that 



2 2 

 U. U. B 



AH =3£ ^-= 6 -^ [~ i ) , (154) 



n n n g r g 'B^ n ' 



in which 6^, is the hydraulic characteristic o£ the reference material. 

 Equation (153) may therefore be written: 



^ n r 



in which the summation is carried out over the n different porous 



materials of the horizontal slice of thickness. Ah.. 



J 



From equation (155) the discharge associated with the slice of 



thickness Ah. is found to be 

 J 



1/2 

 gAH ^ Ah. 



AQ. = U.Ah. = (^-) B ' ,12 ' ^156) 



n r 



and by adding the contributions from all horizontal slices of the 

 trapezoidal breakwater one obtains 



gAH„ ^/^ , Ah 



Q = ^A Q = {-^) h^ E C_g_ -^) . (157) 



n r 



Thus, requiring that the discharges per unit length given by 

 equations (152) and (157) be identical, the width, I , of the equivalent 

 rectangular breakwater is 



85 



