L tan a 



ol 



(83) 



The elapsed time is normalized by the quantity L /e . Although mass is 

 conserved across the boundary between the two solution areas, the gradient of 

 the shoreline is not continuous at this point. 



0.5-1 



e,t 



0.5 1 1.5 2 



ALONGSHORE DISTRNCE (x/L) 



Figure 37. Final shoreline position in the vicinity of a shore- 

 parallel detached breakwater (6 =0.5, a .=0.4 rad , 



«o2 = 0) 

 Shoreline Change at a Seawall 



79. The function of a seawall is to prevent the shoreline from retreat- 

 ing along a specific coastal reach. If the shoreline remains well seaward of 

 the seawall, there will be no influence of the seawall on the shoreline evolu- 

 tion. If the shoreline retreats to the seawall, the location of the seawall 

 determines the minimum allowable shoreline position. If erosion takes place 

 beside a seawall (flanking) , various changes in the shoreline position might 

 occur depending on the characteristics of the seawall and the incident waves. 

 If flanking of the seawall is not possible (see Figure 38) , the solution for 

 the plan shape of an eroded shoreline will be the same as for erosion 

 downdrift of a groin (Equation 64, with opposite sign). In this case, the 

 seawall is functioning as a semi-infinite structure. 



60 



