extended Groin 44 (as discussed for Alternative 2.) The reduced downdrift 

 impacts of Alternative 3 are evident in Figure 24, where the minimum shoreline 

 position erodes to the seawall for a distance of 1.150 ft. much less than the 

 2.500 ft of Alternative 2. Shoreline recession impacting the 75-ft protective benn 

 is presented in Figure 25. Alternative 3 maintains the 75-ft protective berm at the 

 hot spot with the modeled shoreline being located landward of the 75-ft protec- 

 tive berm less than 20 percent of the 6-year simulation. In addition. Alternative 3 

 has reduced spatial and temporal extents of downdrift erosion compared with 

 Alternative 2. Impacts to the protective berm occur to a distance of 3,600 ft 

 downdrift of Groin 44 with the maximum shoreline recession occurring approxi- 

 mately 70 percent of the 6-year renourishment interval immediately downdrift of 

 Groin 44. 



Alternative 3 yields promising results, limiting impacts to the 75-ft protective 

 berm within the hot spot during the 6-year renourishment interval with only small 

 increases in downdrift erosion over Alternative 1 . These results are obtained 

 with the relatively minor expense of extending existing Groin 44. 



Alternative 4. Alternative 4 proposes the addition of four, 280-ft groins 

 between Groins 44 and 45. The function of these groins is similar to that of 

 Alternatives 2 and 3, to impound additional material at the hot spot. The 

 minimum shoreline position presented in Figure 26 is located landward of the 

 target shoreline within the compartments between Groin 44 and Groin 44c (third 

 groin updrift of Groin 44). The target shoreline encroachment in the first com- 

 partment updrift of Groin 44 occurs approximately 65 percent of the 6-year 

 simulation (Figure 27). Observing animations of the calculated shoreline change 

 for Alternative 4, the shoreline erosion within the groin compartments updrift of 

 Groin 44 occurs during reversals in longshore transport direction. 



Erosion downdrift of the added groin field results in the minimum shoreline 

 position landward of the target shoreline for a distance of 2.300 ft downdrift of 

 Groin 44 over the 6-year simulation. Target shoreline encroachments occur most 

 often in winter and spring and least often in fall and summer. Downdrift impacts 

 of Alternative 4 are slightly less severe than those of Alternative 2 and remain 

 considerably larger than the impacts of Alternatives 1 and 3. Encroachment of 

 the shoreline near Groin 44 occurs 70-80 percent of the 6-year simulation. The 

 least severe downdrift impacts appear to occur during the winter months, when 

 reversals in longshore transport act to supply sand to the area. This alternative 

 has relatively high cost and causes substantial downdrift recession. Therefore, it 

 is not recommended. 



Alternative 5. Alternative 5 decreases the groin length of Alternative 4 from 

 280 ft to 1 00 ft with the intent of maintaining the protective berm at the hot spot 

 and reducing downdrift erosion. Figure 28 presents the maximum, minimum, 

 and final shoreline positions for Alternative 5 indicating that the protective berm 

 within the hot spot is eroded within the four groin compartments south of 

 Groin 44. Maximum percentages of protective berm impacts (Figure 29) within 

 the hot spot range from 15 to 75 percent of the 6-year simulation, increasing with 

 distance towards Groin 44. Downdrift impacts for Alternative 5 are reduced to 

 the same levels as Alternative 3, approximately 40-50 percent of the 6-year 



28 Chapter 3 Functional Design 



