,^ «>— Groin 



Figure 5-23. Calculation for downdrift erosion fillet volume, 



are available, the evaluation and design of permeable groins will be inexact. 

 In general, the desired degree of sand bypassing can be achieved as effec- 

 tively and economically by the appropriate design of groin height and length. 



6 . Adjustabl e Groins « 



Most groins are permanent, fixed structures; however, adjustable groins 

 have been used in England and Florida. These groins consist of removable 

 panels between piles. The panels are designed to be added or removed to 

 maintain the groin at a specific height (usually 0.3 to 0.6 meter or 1 to 2 

 feet) above the beach level, thus allowing a part of the sand to pass over the 

 groin and maintain the downdrift beach. However, if the structural members 

 undergo even slight movement and distortion, the removal or addition of panels 

 becomes difficult or even impossible. 



7 . Alinement of Groins . 



Examples may be found of almost every conceivable groin alinement, and 

 advantages are claimed by proponents of each. The maximum economy in cost is 

 achieved with a straight groin perpendicular to the shoreline. Various 

 modifications such as a T- or L-head are included to limit recession on the 



5-53 



