Horizontal Shore 



Section (HSS) 



Intermediate 



Sloped Section 

 (iSS) 



"»., 



MLW (MLLW) 



m^h OCEAN 



Original Beach Profile 



Figure 5-12. Sections of a typical groin. 



(1) Horizontal Sho re Section . This section extends far enough land- 

 ward to anchor the groin and prevent flanking. The height of the HSS depends 

 on the degree desirable for sand to overtop the groin and nourish the down- 

 drift beach. The standard height is the height of the natural berm, which is 

 usually the height of maximum high water, plus the height of normal wave 

 uprush. An economic justification for building a groin higher than this is 

 doubtful except for terminal groins. With rubble-mound groins, a height about 

 0.3 meter (1 foot) above the berm is sometimes used to reduce the passage of 

 sand between large cap stones. The maximum height of a groin to retain all 

 sand reaching the area (a high groin) is the height of maximum high water and 

 maximum wave uprush during all but the most severe storms. Conversely, this 

 section, or a part of it, can be built lower than the berm to permit over- 

 passing of sediment during periods of high tide. A low groin of this type can 

 be termed a weiv groin based on its operational similarity to weir jetties. 

 Design aspects of weir systems are discussed in Weggel (1981). The HSS is 

 built seaward to the desired location of the design beach berm crest. 



(2) Intermed iate Sloped Section. The ISS extends between the HSS and 

 the OS. It should approximately parallel the slope of the natural fore- 

 shore. The elevation at the lower end of the slope will usually be determined 

 by the construction methods used, the degree to which it is desirable to 

 obstruct the movement of the littoral material, or the requirements of 

 swimmers or boaters. 



(3) Outer Section. The OS includes all the groin that extends 

 seaward of the intermediate sloped section. With most types of groins, this 

 section is horizontal at as low an elevation as is consistent with the economy 

 of construction and public safety. 



b. Desig n o f Beach Alinem ent. The first step in the design of a groin or 

 groin system is the determination of the eventual beach alinement. The beach 

 alinement is the orientation the shoreline will take near the groins. In this 

 case the shoreline refers to the berm crest. The best estimation of this 

 orientation is determined by observing fillets at nearby structures with 

 similar coastal processes. If this information is not available, determine 

 the nearshore direction of the predominant wave approach and then assume a 

 beach alinement perpendicular to that direction. As shown in Figure 5-13 

 three aspects, which will be discussed separately, need to be considered: the 



5-40 



