beach. Adjustable groins are reported to be particularly usefial where 

 an atterapt ia being made to widen a beach with a rainiiaura of erosion 

 diiifriage to the coundrift area. However, they are effective only where 

 there is an adequate supply of littoral material, 



1^6, Diraensions of Groins . - The width and side slope of a groin 

 depend on the wave forces to be withstood, the type of groin, the materials 

 with which it is constructed, and the construction methods used. These 

 features are considered under structural design. The length, profile 

 and spacing are important consiaerations with respect to functional success. 



157. The length of a groin is determined by the depths in the off- 

 shore area and the extent to x^Ihich it is desired to intercept the littoral 

 stream. The length should be such as to interrupt such a part of the 

 littoral drift as will supply enough materials to create the desired 

 stabilization of the shore line or the desired accretion of new beach 

 areas. Care must be exercised that these ends are attained without a 

 corresponding damage to doT.jndrift areas. E'or functional design purposes, 

 a groin may be considered in three sections: 



a. The horizontal shore section; 



b. The intermediate sloped section; and 



c. The outer section. 



1^8. The Horizontal Shore Section . - This section would extend from 

 the desired location of the crest of berm as far landward as is required 

 to anchor the groin to prevent flanking. The height of the shore section 

 depends on the degree to which it is desirable for sand to overtop the 

 groin and replenish the downdrift beach. The minimum height of the groin 

 is the height of the desired berm, which is usually the height of maximum 

 high water that occur_s frequently plus the height of normal vjave uprush. 

 The maximum height of groin to retain all sand reaching the area (a high 

 groin) is the height of maximum wave uprush during all but the least 

 frequent storms. This section is nearly horizontal or sloped slightly 

 seaward paralleling the existing beach profile or the desired slope in 

 case a txider beach is desired or a new beach is to be built. 



159. The Intermediate Sloped Section . - The intermediate section 

 would extend between the shore section and the more or less level outer 

 section. This part of the groin should approximately parallel the slope 

 of the foreshore the groin is expected to maintain. The elevation at 

 the lower end of tie slope ^^rill usually be determined by the construction 

 methods used, the degree to which it is desirable to obstruct the move- 

 ment of the material, or the requirements of swimmers or navigation 

 interests. 



160. The Outer Section . - The outer section includes all of the groin 

 extending seaward of the vsloped section. VJith most types of groins, this 



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