9. Wave data were collected on eight electrical resistance wave gages. 

 Wave pressures were measured with miniature semiconductor pressure trans- 

 ducers, each equipped with a silicon diaphragm and a four-arm strain gage 

 bridge. Simultaneous pressure measurements were made at six different loca- 

 tions along the face of the seawall (Figure 5) . Wave signal generation and 

 data acquisition were controlled using a DEC MicroVAX I computer. Wave and 

 pressure data analysis were accomplished using primarily a DEC VAX 11/750. 



Test Conditions 



10. Test conditions were determined based on historical storm records 

 for the Virginia Beach area from 1928 to present. Selection of these condi- 

 tions involved numerical modeling of three hurricanes and three northeasters 

 which were chosen as the most severe storms in the historical record 

 (Lillycrop, Pope, and Abel, in preparation). Portions of the wave hindcast 

 data came from the Sea State Engineering and Analysis System (SEAS) . The re- 

 mainder were obtained from existing Wave Information Studies (WIS) . After a 

 data base was established, all wind wave computations were made using the WIS 

 discrete spectral wave transformation model. This procedure used three hurri- 

 cane storms and three northeaster storms which were considered representative 

 of the worst storms on record. From these six storms, the most significant of 

 each type was chosen to be represented in the physical model. The test storms 

 were, specifically, the hurricane of August 1933 and the northeaster of March 

 1962. These are the most severe storms of record for Virginia Beach, and they 

 were generated using TMA spectra, which are analytical spectra representing 

 the depth and frequency transformations of a deep-water wave moving into shal- 

 low water (Hughes 1984 and Lillycrop, Pope, and Abel, in preparation). A de- 

 scription of the design deepwater wave conditions reproduced in the tank is 



provided in Table 1 for the zero-moment wave height H , wave period T , 

 ^ mo p 



and three spectral shape parameters y , a, , and a, . . Swl's were chosen 

 to bracket historical storm surge elevations, and those selected for testing 

 were +6.0 ft, +7.0 ft, +8.0 ft (project design water level), and +9.5 NGVD. 



11. The wave machine was calibrated by generating monochromatic waves 

 of differing heights and periods while measuring these waves at various gage 

 locations in the tank. In the same manner, spot checks of the TMA spectra 



12 



