end. The degree of obstruction designed for the barrier must take into 

 account the needs of shoreline segments for littoral materials down- 

 drift from the particular area. In order to protect a long shoreline 

 segment, groins are built in series as systems of barriers. 



2. Location on Shore , 



The suspended sediments travel along the foreshore in a band width 

 extending from the breaker zone to the limit of wave uprush. Because 

 the predominant part of sediments travel in the zone shoreward of the 

 6-foot-depth contour, groins are located at the inner margin of this 

 band. Groins should be rooted in the shore landward of the crest of 

 the beach berm sufficiently far to prevent flanking by littoral cur- 

 rents during storm wave attack at times of abnormally high water levels. 

 Connection to a bulkhead or revetment is desirable. The outer ends are 

 usually extended as far as the 6-foot-depth contour at low tide. 



3. Dimensions . 



The range in usual lengths extends from some minimum value less 

 than 100 feet to a maximum of several hundred feet. Heights of groins 

 vary with wave conditions and the degree of obstruction permissible, 

 considering the material requirements of other shore segments downdrift 

 of the particular groin system. 



4. Profile . 



Three sections are recognized along the length of a groin, namely 

 the horizontal-shore section, the intermediate-sloped section and the 

 outer-horizontal section. 



The horizontal-shore section should be secured to a bulkhead or 

 keyed into ground that is not disturbed by attack of severe storm waves. 

 The shore section should extend, as a minimum height, to the level of 

 normal wave uprush above high water. The maximum height required to 

 retain all material reaching this section of the groin is the level of 

 maximiim wave uprush during all but the least frequent storms. 



The top of the intermediate section matches the levels of the hori- 

 zontal-shore section and the outer section. It is parallel to, and 

 corresponds in length with the slope anticipated for the foreshore as a 

 result of material retention by the structure. The outer section 

 extends seaward from the intermediate-sloped section to such a length 

 as is required to contain the intersection of the proposed beach slope 

 updrift of the groin with the existing bottom. The top of the outer 

 section is established as nearly as practicable at the MLW level, 

 usually about 1 foot above it, 



5. Spacing , 



The fillet of sand trapped between groins tends to stabilize along 



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