where 



F = average freeboard, or that distance between the crest of the 

 seawall and the local mean water level 



H = zero-moment wave height measured at Goda Array 2 (wave gages 5, 

 ™° 6, and 7) and assumed to be representative of the H at the 

 toe of the structure 



L = significant wave length associated with peak period T measured 

 P P 



at Goda Array 2 and computed using Hunt's method (Hunt 1979) 



The relative freeboard parameter F' can be thought of as the ratio of free- 

 board to severity of local wave climate. As wave climate becomes more severe, 

 F' becomes smaller until a point is reached when the wall is being inundated 

 with waves such that the energy dissipation through wave/structure interaction 

 is insignificant. To establish data trends for the Phase I and Phase II sea- 

 walls, the relative freeboard parameter was plotted versus the measured over- 

 topping rate Q in cubic feet per second per foot (cfs/ft) of seawall. 



22. The Phase I and Phase II tests were limited to a relatively narrow 

 band of wave conditions because only two peak periods, and corresponding maxi- 

 mum wave heights, were specified in the selected design events. To better 

 establish data trends and cover a wider range of possible storm conditions, 

 wave heights of the wave board were varied for the two specific wave periods 

 at each of the selected swl's (see Appendix A). Figures 7 and 8 show that as 

 the percent gain of the design wave height at the wave board was increased, 



the wave energy of the spectrum, or H , measured at Goda Array 2, 



mo 



approached an approximate limiting value (Hughes 1984). This theoretical 

 approximate li 

 calculated by 



approximate limiting value of H is controlled by the water depth and is 



mo 



H = B h (2) 



mo , . 

 (max) 



where B is dependent on the fronting beach slope and typically ranges from 

 0.55 to 0.65, and h is the water depth. A value of B = 0.6 is suggested 

 for a typical beach slope and was used along with the water depth and asso- 

 ciated setup to plot the limiting value lines seen in Figures 7 and 8. These 

 plots indicate that the maximum amount of energy for a particular water depth 

 was reached at the higher percent gains. 



23. The Phase I seawall (Figure 5a) was initially tested for hurricane 

 and northeaster storm events, as previously described, for swl's of +6.0 ft, 



19 



