Initial Shoreline , t = 



Figure 38. Definition sketch of the Pelnard-Considere model 

 of shoreline evolution near a groin or jetty 

 (after LeMehaute and Soldate, 1977). 



where 



y g = distance the shoreline has moved seaward from its original straight 

 configuration 



x = distance updrift from the jetty or groin 



t = time since construction of the jetty 



au = angle the wave crest makes with the original shoreline 



e/k is a factor which depends on the offshore profile and wave conditions and 

 was reported by Bakker (1968a, 1968b) to be approximately 4.3 x 10 6 cubic feet 

 per year for an ex posed location along the coast of Holland (The Netherlands). 

 Th e vari able E(x//4te/k) is the error function complement of the argument 

 x//4te/k and is tabulated in numerous handbooks of mathematical tables (e.g., 

 Abramowitz and Stegun, 1964). The solution given by equation (17) describes 

 the updrift shoreline until the time when the shoreline at the jetty reaches 

 the end of the jetty; this time is given by 



I 2 TTk 



t' = 



4e tan 2 a v 



(18) 



After the time, t^ t', the jetty no longer retains all the sand moving into 

 the fillet but bypasses a part of it. The amount of sand bypassed increases 

 with time until the fillet is full (a straight shoreline built out to the end 

 of the jetty), at which time all the sand approaching the structure is by- 

 passed. After the sand begins to bypass but before the beach fillet is full, 

 the shoreline is given by 



57 



