0.2 0.4 0.6 0.8 



ALONGSHORE DISTANCE (x/W) 



Figure 33. Shoreline evolution between two groins initially 



filled with sand (L/W = 0.33 , a = 0.25 rad) 



o 



From Equation 71, the sand bypassed (discharge rate) at x = W can be 



obtained. The sand transport rate as a function of time can be written (if it 



is assumed that tan a « a ) 

 o o 



Q( 



t) = 4Q a V (-l) n „ | .. 

 o o Z^ (2n + l)n 



-e(2n+l) 2 ir 2 t/4W 2 



n=0 



(73) 



for t > and x = W . 



In Equation 73, the quantity 2Q a is the sand transport rate along a 

 straight beach exposed to the incident breaking wave angle a . (This is the 

 transport initially existing when the groin compartment is completely filled.) 

 If Q in Equation 73 is normalized with this quantity, the bypassing sand 

 discharge at the downdrift end groin is conveniently displayed in dimension- 

 less form. Figure 34 shows such a curve. 



54 



