approach direction at the -3-ft mean low water (mlw) contour are presented in 

 Table A3 for each design event. The design water depth at that location 

 includes the corresponding storm surge plus a 1-ft astronomical tide. 



Table A3 



Design Wave Conditions 



Event 



Wave Height (H,. ft) 







Period (sec) 



Direction 



1 -year 



5.0 



5.6 



SSE 



1 0-year 



5.6 



6.5 



SSE 



25-year 



6.5 



7.6 



SSE 



50-year 



7.2 



9.7 



SSE 



Sediment transport 



Longshore transport. Preliminary analyses of aerial photos and wind 

 distributions indicated that the predominant net longshore littoral drift in the 

 project area is small and in a northerly direction. To gain a better insight into 

 this process, several techniques were used. 



Energy flux method. This method is based on the assumption that the 

 longshore transport rate of littoral material can be computed from the 

 longshore component of energy flux in the surf zone according to the 

 following equation: 



Q = 7500 P u 



(Al, Equation 4-50, SPM) 



The longshore energy flux in the surf zone is approximated by assuming 

 conservation of energy flux in shoaling waves, using small-amplitude wave 

 theory, and then evaluating the energy flux relation at the breaker position. 

 This energy flux is then related to sediment transport through an empirical 

 relationship. The procedure used in this type of analysis is to first develop the 

 wave climate for an area, consisting of wave heights, periods, and breaking 

 wave angles between the wave crests and the shoreline and the percent 

 occurrence of these conditions. These wave parameters are then used in the 

 empirical relationship to determine the amount of sediment that could be 

 transported by each wave condition. 



For this analysis, each wind speed and direction combination was applied 

 to the wave model grid, yielding a nearshore wave height/period/direction 

 combination resulting from that wind. These wave characteristics were 

 converted to longshore energy flux potential and transport potential and 

 weighted by their individual probability of occurrence. Summing the relative 

 contributions of the wave resulting from each wind speed/direction 

 combination yielded a net longshore sediment transport potential of 

 13,300 cu yd traveling northerly along the Bay Ridge shoreline. 



Appendix A Case Design Example of Detached Breakwater 



A5 



