This general equation not only includes the incident wave height and period, 

 water depth, and seawall freeboard but also provides a means for comparing 

 seawall performance and predicting percent differences in the overtopping 

 rates for various beach erosion levels in front of the structure. Such com- 

 parisons will be made later in this report. 



24. CENAO indicated that the overtopping rates measured for the Phase I 

 seawall were not satisfactory and requested suggestions of how the overtopping 

 could be reduced. Suggestions considered were to: (a) increase the crest 

 elevation of the wall, (b) place a large revetment in front of the wall, and 

 (c) change the geometry of the seawall) . Item (a) was believed to be the most 

 promising but was rejected by CENAO because of local community objections. 

 Placement of a large revetment in front of the wall was deemed impractical and 

 uneconomical; thus, it was recommended that the geometry be changed by adding 

 a lip, or extension, to the recurved portion of the seawall. This alternative 

 was agreeable with CENAO, and a modified seawall geometry developed by CENAO, 

 Phase II seawall, was constructed for testing. 



25. The Phase II seawall (Figure 5b) was tested using hurricane and 

 northeaster storm events for swl's of +7.0, +8.0, and +9.5 ft NGVD. All data 

 generated from the Phase II seawall tests (including data from wave heights of 

 30 to 100 percent of DWHAWB are presented in Figure 10 and tabulated in 

 Table A2 (Appendix A). Similar to the Phase I seawall test results, these 

 data fit the general trend of Equation 3. Since there was some question 

 whether the prototype overtopping rates for the design events should be based 

 on all the data generated in the Phase II tests (wave heights of 30 to 



100 percent DWHAWB) or with only the 100 percent DWHAWB data, a Q versus F' 

 plot of only the 100 percent DWHAWB data for Phase II seawall is presented in 

 Figure 11. This plot contains fewer data points because of the limited number 

 of design events, but the data trend characteristic of Equation 3 is assumed. 



Seawall Comparisons 



26. To compare the performance of the Phase I and Phase II seawalls. 

 Equation 3 was used. An explanation of Equation 3 and a tabulation of 

 calculated values are presented in Appendix B, Specific comparisons of the 

 percent decrease in Q for hurricane conditions at the three swl's tested are 

 given in Table 2. Since only wave heights up to 70 percent of the DWHAWB at 



23 



