Phase II testing were 24 to 48 percent less than corresponding rates measured 

 with the Phase I seawall in place. 



45. At the higher water levels of +8.0 and +9.5 ft, the riprap fronting 

 berm appeared visually to have less influence on the reduction of overtopping 

 rates; however, general observations with and without the berm in place indi- 

 cated that the structure did reduce overtopping at the +7.0-ft swl. Without 

 further tests it is hard to say how much the overtopping rates would be af- 

 fected, without the berm in place, at the higher water levels. Also, the 

 presence of the berm could help to reduce beach scour at the seawall by help- 

 ing to dissipate incident/reflected wave energy. Tests indicated that 

 1,000-lb stone were of adequate size to ensure berm stability under the storm 

 conditions tested. 



46. Wave setup and seiches did occur in the wave flume, and these phe- 

 nomena were considered during data analysis. The seiche influence was respon- 

 sible for much of the scatter evident in the presentations of the overtopping 

 data. This influence was not great enough to affect overall data trends. 



47. Results of the pressure tests indicate that wave pressures in ex- 

 cess of 100 psi can be experienced on the seawall under severe wave condi- 

 tions; however, these pressures in excess of 15 psi characteristically have 

 durations of less than 20 msec. The question remains — at what duration can a 

 designer confidently establish a threshold above which pressure magnitudes are 

 considered of serious importance? Presently, the answer is a matter of per- 

 sonal opinion. Some individuals (Carr 1954, Cole 1972, Garcia 1968, and Ross 

 1953) who have investigated this problem feel that the lesser secondary pres- 

 sures of longer duration are more critical for designer purposes. These par- 

 ticular tests identified secondary pressures with magnitudes of approximately 

 5 to 10 psi and durations in the range of 2.0 to 3.0 sec. 



48. Although the geometry of the seawall prevented installation of a 

 vertical transducer in the extreme upper curvature of the wall, the area did 

 not appear to be subjected to large pressures. Visual assessment of the test- 

 ing indicated that this was not an area where wave energy was being concen- 

 trated. Similar tests performed on the Cape Hatteras Lighthouse seawall indi- 

 cated that this was an area of concern due to the pressure magnitudes measured 

 on the overhang (Grace and Carver 1985). However, that particular design in- 

 corporated a 2-ft extension to the original overhang. In comparison, the lack 



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