Design alternatives 



Maintaining the boundary conditions and transport coefficients from the final 

 calibration, design alternatives were configured and evaluated with GENESIS. 

 The evaluated design alternatives are summarized in Table 2. The shoreline 

 response to each alternative was simulated with a 6-year wave record developed 

 from the 3-year record of directional waves measured at Long Branch. New 

 Jersey, as described in a previous section. 



Alternative 1. This alternative introduces no structural modifications within 

 the hot spot at Monmouth Beach. The CP&E (1997) report specifies nourish- 

 ment intervals of either 2 or 3 years for this alternative. In keeping with a design 

 objective of the New York District to limit beach fills to the prescribed 6-year 

 nourishment interval, no additional beach fills were included in this alternative. 

 The shoreline response of Alternative 1 is expected to resemble the shoreline 

 response of Contract 1 A immediately following beach-fill placement. The model 

 simulation includes the feeding potential of the beach fill constructed south of the 

 hot spot, and the simulated shorelines will differ from the observed shoreline 

 changes because of the influence of this sediment supply. 



Animation of the time sequence of shoreline response during the year follow- 

 ing beach-fill placement reveals similarities between the modeled response and 

 observed response of the beach fill. The GENESIS simulation indicates rapid 

 erosion of the beach fill between Groins 44 and 45 immediately following place- 

 ment of the fill, in addition, the region north of Groin 44 experiences an initial 

 shoreline advance. These two simulated qualitative behaviors are observed in 

 aerial photography and beach profile surveys following fill placement under 

 Contract lA. 



Minimum, maximum, and final shoreline positions for Alternative 1 are 

 presented in Figure 20. The shoreline within much of the hot spot recedes 

 landward of the design-specified shoreline at some time during the 6-year 

 simulation. However, monitoring of the minimum shoreline position occurring 

 during the 6-year period is not an adequate methodology for describing the 

 performance of a design alternative. The time during which the target condition 

 (a 75-ft protective benn) is violated accounts for duration of the unwanted 

 condition and is considered a more realistic and accurate measure of the 

 effectiveness of an alternative. Therefore, the percentage of the 6-year 

 simulation in which the modeled shoreline position is located landward of the 

 shoreline required to maintain a 75-ft benn is computed and presented in 

 Figure 2 1 . 



The cumulative time in which the simulated shoreline within the hot spot is 

 located landward of the target shoreline is approximately 70 percent of the 

 simulation. Downdrift of Groin 44, the shoreline recedes landward of the design 

 berm approximately 40 percent of the time. Spring and winter have the highest 

 percentages of design berm violations within the hot spot. Spring and summer 

 have the highest percentages of design violations downdrift of Groin 44 because 

 of predominant longshore transport directed to the north and the consequential 



24 Chapter 3 Functional Design 



