700 



Shoreline position (ft) 



600- 

 500- 

 400 

 300 

 200 

 100 

 



Grolns+breakwaters r?-r7\ 

 Only breakwaters u-m 



Only groins w-7-r\ 



Only extended groins rzi^ 



400 600 800 1000 



Distance alongshore (ft) 



1200 



Figure 46. Shoreline change for alternative configurations 



409. On the downdrift (east) end of the fill, the simulation indicated 

 that the groin there is essential for retaining the beach. After removing the 

 east groin, the shoreline receded about 210 ft at the eastern project bound- 

 ary. At the same time, the whole area lost 50,000 cu yd, only slightly less 

 than the amount lost in the alternative without breakwaters. 



410. As the third hypothetical alternative, a simulation was made to 

 investigate the length of the two terminal groins required to hold the beach 

 in place to the same extent as the existing condition of combined groins and 

 breakwaters. (Again, it is emphasized that cross -shore transport is not 

 accounted for in this comparison; a tendency for fill to be transported 

 offshore is considered to be a significant factor in the Great Lakes.) As 

 indicated in Figure 46, the western groin had to be extended by 210 ft and the 

 eastern groin by 320 ft to produce a net loss of sand of 285 cu yd (50 cu yd 

 less than in the existing condition). Thus, according to the calculations and 

 omitting consideration of cross-shore transport, it would be possible to build 

 another 530 ft of groins rather than 750 ft of detached breakwaters to hold 

 the beach fill in place. Since construction of groins is naturally shore- 

 based, the groins are located in shallower water than the breakwaters over a 



174 



