PART II: THE MODEL 

 Scale Selection 



7. During this model study, time constraints dictated that construction 

 of the physical model be carried out prior to determination of ultimate test 

 conditions (by CERC's Coastal Oceanography Branch). Under these conditions a 

 model to prototype scale of 1:13 was chosen based on calculations indicating 

 that any smaller scale would introduce scale effects into the secondary task 

 of optimizing a stable fronting riprap design; therefore, Phase I seawall 

 overtopping tests were performed at the 1:13 scale. However, after the design 

 test conditions were eventually chosen, it was found that at a scale of 1:13 

 only 60 percent of the design deepwater zero moment wave height H * could 

 be consistently achieved at the wave board for all representative swl's. At 

 this time it was believed that overtopping was controlled by the inshore con- 

 ditions. Because visual and measured observations indicated maximum wave 



heights and H values were being maintained, tests were continued at this 

 mo 



scale. After changes in the geometry of the seawall had been recommended, 



however, the decision was made to implement a smaller model scale of 1:19 to 



achieve 100 percent of the design H at the wave board in deep water. Also 



mo 



at this point, a stable riprap size had been determined; therefore, all 

 Phase II testing was performed at a model scale of 1:19. (In this report. 

 Phase II implies that geometric modifications to the seawall had been incor- 

 porated.) Pressure tests conducted for the Phase II seawall were conducted at 

 the 1:19 scale. 



Equipment and Facilities 



8. All tests were conducted in a concrete wave flume 11 ft wide and 

 250 ft long. The cross section of the tank in the vicinity of the structure 

 was partitioned into two 3-ft-wide channels and two 2.5-ft-wide wave-absorbing 

 channels (Figure 4) . Irregular waves were generated by a hydraulically actu- 

 ated piston-driven wave board. The seawall test sections were installed in 

 the flume approximately 200 ft from the wave board. 



* For convenience, symbols and abbreviations are listed in the Notation 

 (Appendix E) . 



10 



