overtopping^ Due to the low freeboard between the 1991 beach profiles 

 and seawall crest elevations, waves overtopping the seawall tended to 

 flow over the wall in a bore rather than be deflected vertically as in Tasks 

 A, C, and C+. Because the water movement was horizontal rather than 

 vertical, wind effects are not expected to be significant. 



Due to high reflection coefficients from the high seawall freeboard in 

 models of the 1978 profile, wave energy reflected from the seawall re- 

 mained in the wave flume and increased the total energy in the flume over 

 time. Avoiding this effect would require that each test run be terminated 

 before energy reflected from the structure could reach the wave generator 

 and return to the structure. Each test then would be on the order of 2 min, 

 after which the testing would be halted until the energy in the flume had 

 dissipated. A series of short tests then would be used to ensure that the en- 

 tire wave spectrum was represented. Again, this level of accuracy is prob- 

 ably not justified, and would be time-consuming and expensive. The 

 probable effect of this increased energy level in the flume is an increase in 

 overtopping rates for the 1978 profile tests. 



Because of the low seawall freeboards and extended beach profiles 

 compared to Tasks A, C, and C+, reflection coefficients for Task B were 

 small and reflected wave energy was not a significant factor in the tests. 



Memorandum lo Joan Pope entitled "Assessment of wind effects on wave overtopping 

 of proposed Virginia Beach seawall," 1987, from Donald T. Resio, Offshore and Coastal 

 Technologies, Inc., Vicksburg, MS. 



Chapter 4 Discussion of Research Tasks A, B, and C 



45 



