major portion of the structures, and less stone would be required, the groin 

 extension alternative would be less expensive to build than the detached 

 breakwater alternative. However, in the extended groin case, it is probable 

 that offshore losses produced by steep waves and rip currents tending to form 

 at groins would make the relative performance of the groins much inferior to 

 detached breakwaters for containing the beach. The long groin alternative was 

 rejected by the Corps of Engineers (USAED, Buffalo 1975) because of potential 

 impacts on adjacent shores. 



411. In conclusion, the simulations confirm that the combination of 

 detached breakwaters and terminal groins is superior to simpler designs in 

 holding the beach fill in place. Both the groin-only design and segmented 

 detached breakwater -only design perform poorly, causing about half of the fill 

 to be lost in 1 year, which is unacceptable. 



Five -Year Simulation 



412. It is interesting to perform a 5 -year simulation with the cali- 

 brated model since shoreline position data are available for this period. 

 Normally, such a long-term projection would be one of the objectives of a 

 design study, whereas in the present case the simulation provides further 

 verification of the model. In this illustrative case study, only a 1-year- 

 long wave data file is available, precluding estimation of a likely range of 

 predicted shoreline positions resulting from possible variations in the wave 

 climate. Also, the time dependence of YG1 , associated with the pocket beach 

 to the west of the project, is unknown. The calibrated model was used with 

 the distance YG1 = 90 ft to give the average annual fall trend of a net gain 

 of 2,500 cu yd. 



413. Figure 47 plots calculated annual net volume for the 5 -year 

 simulation extending from 24 October 1977 to 14 December 1982. The average 

 net annual gain in volume was 2,400 cu yd, close to the trend in fall measure- 

 ments of 2,500 cu yd. The measurements show a net gain of 3,300 cu yd for the 

 second year, reduction to 2,500 cu yd in the third and fourth years, and a 

 further reduction to 2,000 cu yd in the fifth year. The measurements show 



175 



