The homogeneous rectangular breakwater consists of a reference 

 material of stone size, d^, and hydraulic characteristics, 3^.. The 

 reference material should be taken to be representative of the porous 

 materials of the multilayered breakwater. To find the discharge per 

 unit length of the rectangular breakwater, the flow is assumed to be 

 essentially horizontal and one obtains 



AH 



Pg 



Pg^ U 



C151) 



in which l^ is the width of the equivalent breakwater and AH^ is the 

 head difference defined in Figure 23. The discharge per unit length is 

 therefore obtained from equation (151) to be 



gAH 1/2 h 

 Q = Uh = i—^} -^ 



(152) 



To evaluate the discharge per unit length of the trapezoidal, 

 Llayered breakwater a \ 

 schematically in Figure 24. 



multilayered breakwater a horizontal slice of height, Ahj , is shown 



P/yog 



T 

 Ahi 



Figure 24. Horizontal slice of thickness. Ah., of multilayered 

 breakwater. 



This horizontal slice consists of segments of the different porous 

 materials of lengths ly^. From an assumption of purely horizontal flow 

 it follows that the discharge velocity of the slice considered, U., must 

 be the same in all segments and the total head loss across the breakwater 

 must be equal to AH^, the head difference shown in Figure 23. From this 



84 



