each 30-sec cycle, sufficient time was provided for stilling of the water sur- 

 face before the next cycle was begun. During this stilling time, observations 

 of the structure's response to the previous cycle were recorded by the model 

 operator. These observations included any movement occurring on the structure 

 and a general statement of the condition of the structure at that point in the 

 test. Structural responses to the hydrographs were also documented by before- 

 and after-testing photographs (Photos 1-30). 

 Wave pressure tests 



12. After an adequate revetment design was determined, the revetment 

 test section was rebuilt. The seawall was then instrumented in preparation 

 for the wave pressure measurements. 



13. The first series of pressure tests for each seawall consisted of 

 recording pressures at several locations along the face of the wall for vari- 

 ous wave conditions and water levels. Because simultaneous measurements were 

 made at several locations on the wall, the capabilities of the microcomputer 

 system limited the sampling rate to approximately 200 samples per second. It 

 was realized that this sampling rate could be insufficient to record the very 

 highest peak pressures that occur in the millisecond range; however, SAW 

 structural engineers indicated that the sampling range was sufficient for 

 their needs because they did not feel the prototype structure would have time 

 to respond to the high-frequency forces. 



14. Pressure data were also taken on oscillograph records as a backup 

 system to the microsystem. Results from the two different recording systems 

 were cross-checked to assure the best possible measurements. 



15. In a typical test, the wave generator was first started. Three 

 waves were then allowed to strike the structure. Between the third and fourth 

 crests, pressure measurements were initiated. The microcomputer system 

 stopped sampling 15 sec later and the wave generator was stopped 30 sec after 

 it was started. The oscillograph recorded time-pressure distributions for all 

 waves except the first three. After each 30-sec test, sufficient time was 

 provided for stilling of the flume before the next test was begun. During 

 this stilling time, water from the test flume was pumped over the face of the 

 seawall to prevent thermal drift of the instrumentation located above the swl. 



16. Results of this first series of tests were used to select the best 

 overall seawall alternative. Following this selection, the four most critical 

 waves that produced the greatest pressures on the selected seawall were chosen 



13 



