Updriff 

 Shoreline 



I Intermediate Oowndrift 



I Shoreline ' 



L ! 



Adjusted Shoreline {^ /Adjusted Shoreline 



Shoreline 



iitii*i*aji^tiii^' 



Direction of Net Longshore 

 Transport 



Wove Crest of 

 Predominant Wave 



Figure 5-13. Three cases of a groin-adjusted shoreline. 



updrift shoreline, the downdrift shoreline, and the intermediate shoreline or 

 the shoreline between two groins. The principles regarding the updrift shore- 

 line can apply to the shoreline updrift of a single groin or the updrift groin 

 of a groin system. Similarly, the downdrift shore alinement can apply to the 

 area downdrift of a single groin or a groin system. The concept of an updrift 

 and downdrift direction assumes there is a predominant direction of longshore 

 transport. The case where there is significant reversal in direction of long- 

 shore transport will also be discussed. 



(1) Updrift Shore Alinement . An estimation of the shore alinement on 

 the updrift side of a groin is illustrated in Figure 5-14. The seaward end of 

 the adjusted shoreline is set at the seaward end of the HSS, point u in the 

 figure. The adjusted shoreline then extends upcoast to meet the original 

 shoreline which thus forms the updrift fillet. 



(2) Intermediate Shore Alinement . The intermediate shore alinement 

 can be estimated by establishing the shoreline (berm crest line) at the 

 seaward end of the HSS of the downdrift groin of the groin compartment 

 (Fig. 5-15, point u) . The shore alinement then extends parallel to the 

 predominant wave crest alinement to point t on the updrift groin. This 

 adjusted alinement generally requires additional sand because the adjusted 

 shoreline at the downdrift side of the updrift groin will recede and could 

 flank the inshore end of the groin. The source of the additional sand can be 

 from either the natural longshore transport or artificial fill. The shoreline 

 will begin alining itself to the wave climate as soon as the groin 

 construction is begun. Therefore, where additional sand is needed to stabilize 

 the shoreline, the initial shoreline will be the realinement of the original 

 shoreline; i.e., area A in Figure 5-15 will equal area B . A and B are 



5-41 



