47. Although the swl's are the same for both classes of storms at +8.0 

 NGVD, the overtopping rate for the hurricane is higher. This occurrence is 

 due to steeper wave conditions which are more characteristic of tropical 

 storms. However, a comparison of the duration of overtopping (Figure 3) shows 

 that overtopping continues for a longer period of time during the extra- 

 tropical storm. During this storm, approximately 9 hr of overtopping and 

 flooding occur as opposed to 5 hr during the hurricane. This increased 

 overtopping duration is due to the length of the storm spanning several tidal 

 cycles compared to the typically faster moving tropical storms. For this 

 reason, not only are the maximum rates important but also the total volume 

 associated with each storm event. 



48. As described in section V, using only the storm data at 95 and 

 100 percent gain, the RFM was used to adjust the shallow-water wave height 

 for the various water depths and to calculate overtopping. Then a change 

 in percent between the overtopping rates for the two bottom elevations was 

 calculated. Table 6 presents this percent reduction in overtopping for each 

 swl which was applied to the actual overtopping rates measured in the model 

 tests. New regression curves were calculated and overtopping hydrographs 

 prepared. 



49. The decrease in water depth when the berm elevation was raised to 

 +3.4 ft NGVD significantly reduced both the maximum overtopping rate and the 

 duration of overtopping. Results of the hurricane at an 8.0- and 9.5-ft NGVD 

 surge level are presented in Tables 8 and 9. Only the hurricane data were 

 recalculated for the 3.4-ft elevation because the hurricane represents the 

 maximum design storm with respect to overtopping. 



50. Results of the wind-induced overtopping study suggest that over- 

 topping rates computed using the SPM (1984) result in conservative predic- 

 tions. Table 10 summarizes the contribution due to wind on total overtopping 

 as computed using the SPM procedure and Resio's visual observation correction 

 factor. 



51. An earlier method recommended by Resio as a very generalized rule 

 of thumb was used for Roughans Point (Hardy and Crawford 1986) which has a 

 similar freeboard range as was used in the Virginia Beach seawall design. 

 This method reduces the predicted wind effect contribution from the SPM to 

 overtopping by 70 percent for each water level. This reduction would produce 

 values closer to those calculated using Resio's observed potential for 



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