erosion downdrift of Groin 44. Tiie greatest impacts to the protective berm 

 appear within the hot spot, and impacts downdrift of Groin 44 are somewhat 

 smaller. 



The sand transported north from the constructed beach fill to the south 

 reduces the rate of erosion experienced at the hot spot prior to completion of the 

 beach fill. However, the 75-ft protective berm within the hot spot experiences 

 erosion during the 6-year renourishment interval. This alternative is attractive in 

 that it requires no additional costs and has the least detrimental influence 

 downdrift of Groin 44. A disadvantage of this alternative is the incomplete 

 protection to the hot spot. 



Alternative 2. Alternative 2 is defined by construcfion of a 350-ft-long 

 extension of Groin 44. The extension is perpendicularly oriented to the seawall 

 and attached to the existing tip of Groin 44. The function of the groin extension 

 is to impound a greater quantity of sand within the area between Groins 44 and 

 45, providing additional protection to the hot spot. 



Structure permeability for extended Groin 44 is expected to vary between the 

 existing and added portions of the structure. The curved nature of the existing 

 structure produces a large fillet and shelters sand adjacent to the groin from the 

 mobilizing forces of waves and runup. The groin e.xtension seaward of the 

 existing tip will be more exposed to the mobilizing forces of waves and runup 

 and therefore is assumed to be more permeable than the existing structure. 

 GENESIS allows only a single value of groin pemieability to be assigned to each 

 structure; therefore, an estimate of the composite groin permeability must be 

 assumed for the extended structure. The extended structure should have perme- 

 ability within the range of existing structures in good condition (0.3) and the 

 nearly impermeable existing Groin 44 (0.0). Simulations of Alternative 2 assume 

 a composite groin permeability of 0.2, but simulations varying permeability 

 between 0.0 and 0.3 were conducted for sensitivity analysis. 



The extended groin functions as intended in the model simulations impound- 

 ing sand a considerable distance seaward of the design berm (Figure 22). How- 

 ever, significantly increased downdrift shoreline recession because of the groin 

 extension is evident. During the 6-year simulation, the shoreline erodes to the 

 seawall for a distance of approximately 2,500 ft downdrift of Groin 44. 



Figure 23 indicates that the shoreline remains seaward of the design benn 

 limits within the hot spot for nearly the entire 6-year simulation. The downdrift 

 shoreline, however, is eroded beyond the design berm limits between 70 and 

 80 percent of the 6-year simulation to a distance 2,000 ft north of Groin 44. 

 Although this alternative meets the requirement of maintaining a protective benn 

 within the Monmouth Beach hot spot, the significant downdrift recession induced 

 by the groin extension may not be considered acceptable. 



Alternative 3. Alternative 3 is a variation on Alternative 2 in which 

 Groin 44 is extended 100 ft. This alternative is proposed to retain the protective 

 berm at the hot spot, while reducing the detrimental downdrift impacts found for 

 Alternative 2. Alternative 3 used a composite structure permeability of 0.2 for 



26 Chapter 3 Functional Design 



