should be such that waves from the northeast (the predominant winter wave 

 direction) will be significantly blocked to prevent loss of the fill, and at 

 the same time allow southerly wave-induced transport to continue during the 

 summer, preventing project-induced erosion north of the rock outcrop. The 

 structure configuration must also prevent tombolo formation when subjected to 

 either seasonal wave condition. To facilitate marine-based construction and 

 provide enough room for salients to form, the breakwater is positioned 200 m 

 seaward of the alignment of the updrift beach and artificial fill, in 3 m of 

 water. From a refraction analysis, the orientation of each of the predominant 

 winter and summer wave crests at the segments is determined. The breakwater 

 segments are aligned perpendicular to the predominant winter waves to provide 

 maximum protection during the winter while allowing a slightly greater propor- 

 tion of energy through during the summer. Each segment should have a length 

 between two-thirds and one-half the distance offshore and 125 m is deemed 

 appropriate. The percentage of predominant wave energy blocked during the 

 winter months is estimated to be 50 percent and the projected gap size is 

 approximately 125 m. If too much fill is lost the gaps can subsequently be 

 narrowed. During summer months this configuration will have an effective 

 width of 160 m. This should provide enough energy transmission to prevent 

 tombolo formation and avoid problems to the northern beaches. The average 

 orientation of each salient is formed by the predominant net wave direction 

 with the apex of each salient located slightly downdrift of the midpoint for 

 each segment. Although the precise size and shape of the expected salients 

 for any instant of time cannot be determined, a projected average condition is 

 shown in Figure B2 . The shoreline south of the project is expected to retreat 

 slightly in response to a reduction in the quantity of sediment normally sup- 

 plied by erosion of the park frontage. Some placed fill will be lost to down- 

 drift areas, thus reducing this adverse impact. The segments are designed to 

 be impermeable and overtopped infrequently. Construction of the segments 

 should progress from south to north. 



Problem 3: Design for Uniform Shoreline Advance 



Problem 



6. Storm erosion protection is to be provided to a highly developed 

 2,000-m-long open coast. Protective beach fills have previously been con- 

 structed, but the material is continually lost to the offshore during winter 



B4 



