storms, and periodic nourishment has become too expensive. Very little ero- 

 sion can be attributed to longshore transport because the predominant wave 

 direction is approximately normal to the shore, and there are no local lit- 

 toral barriers. During the summer, a change in wave conditions causes the 

 shoreline to advance approximately 15 m. The project plan is to retain a 

 beach with a shoreline 30 m seaward of its normal summer position, even during 

 winter storm conditions. 

 Solution 



7. A breakwater plan which creates large variations in the shoreline 

 planform cannot be utilized because it will probably cause shoreline recession 

 opposite the gaps, and will not provide uniform protection along the project. 

 Therefore, a design for uniform shoreline advance will be investigated. An 

 indication of the desired energy reduction is found by comparing the summer 

 wave climate (found to have a predominant breaker height of 1.0 m and period 

 of 8 sec) with the predominant winter waves (1.5 m breaker height and 7 sec 

 period) and noting the summer shoreline advance. Thus, a reduction in wave 

 height of 33 percent and a slight increase in period should advance the shore- 

 line 15 m. It appears that greater reduction is needed (approximately 60 per- 

 cent) , to permit stabilization of the shoreline 30 m seaward of its present 

 location. Because the region has only a slight longshore sediment drift a 

 uniform shoreline advance of 30 m appears feasible. The structure is placed 

 300 m offshore in 5 m of water, well outside the normal winter breaker line. 

 If the structure is designed to transmit only 40 percent of the wave energy 

 during winter storms by overtopping, even less will be transmitted during 

 summer conditions and tombolos may begin to form. Therefore, overtopping is 

 not a viable option for controlling wave transmission. A highly segmented 

 design with segments roughly 30 m long and gaps 20 m wide, requiring at least 

 44 segments to cover the project, could create a more uniform shoreline ad- 

 vance. Each segment should be impermeable and overtopped infrequently. A 

 combination of increased structure permeability and overtopping to increase 

 wave transmission is also a feasible option, but field tests of the struc- 

 ture's cross section and data on the wave climatology are needed. A suffi- 

 cient volume of beachfill is required to advance the shoreline 30 m; plus an 

 overfill allowance is required to replace initial losses. Terminal groins may 

 be necessary if alongshore losses are anticipated. A schematic of the project 

 planform and expected shoreline is illustrated in Figure B3. 



B5 



