Illegal positioning of structures 



329. Figure 31 illustrates the major restrictions on placement of 

 structures. Groins must be placed at least two grid cells apart (upper left 

 sketch). (Since groins in the field are typically placed one to two groin 

 lengths apart, this is not a serious limitation.) A groin cannot be placed in 

 the cell adjacent to a boundary cell, whether the boundary is a groin or a 

 pinned beach (upper right sketch) . Diffracting structures of any type cannot 

 overlap (lower left and lower right) (except at their tips; Figure 30). 



GROINS SEPARATED BY 

 LESS THAN TWO CELLS 



( 



9 '/ 



YA ya 



ADJOINING CELLS 

 ONE CELL 



if 



GROINS PLACED NEXT 

 TO A LATERAL BOUNDARY 



— GROIN AT 

 i=1 



PINNED BEACH 

 AT N+1 



24 25 27 



N N+1 



DIFFRACTING GROIN BEHIND 

 A BREAKWATER 



JNWWWW-) 



J 



J 



TIPS OF BREAKWATERS OVERLAP 



DISTANCE ALONGSHORE/GRID CELL NUMBER 



Figure 31. Example illegal structure placements 



141 



