channel in which, the water level was measured (¥±g. 1]; the pile was 

 fixed in the tank at a specific g. With, a circular pile, the aJigle 

 a specifies th.e location of a point on the circumference with, respect 

 to the direction of wave incidence (Tig. 1). 



Because of the size of available water level gages, the cross sections 

 of most piles are larger by about a factor of two than required by the 

 model scales, if common nearshore piles are considered the prototype 

 (see Table 3). The importance of inaccuracies in modeling the prototype 

 situations in thes? laboratory tests is evaluated in Section IV, The 

 variations introduced into the wave records by the type of wave gage 

 and its exact location near the test pile are evaluated in Appendix A. 

 Each evaluation indicates the reliability of the reported conclusions 

 concerning wave transformation at surface -piercing piles. 



3. Record Analysis and Data Displays . 



The electrical gage records show the incident waves generally have 

 a markedly nonsinusoidal profile (see App. B) . The primary crests are 

 usually smooth, but secondary crests occur. The flow transformation 

 near the pile can introduce additional complications. This is shown in 

 Figure 4, which displays records of water level in time associated with 

 the incident and transformed waves in several test situations. 



Peak water above the Stillwater level (SWL) was measured from water 

 level records of the transformed wave; the average crest height, W, 

 above the SWL is the important dimension of the incident wave. The 

 transformation^ of the sl_owly varying peak forward flow at the pile is 

 measured as W(a) or W(6), the average peak water level or crest 

 height above SWL at a certain orientation angle. This method of data 

 reduction retains only the upper envelope of the recorded wave transfor- 

 mation, ignoring the generally complicated trough flow effects. Figure 5 

 shows the waveform dimensions that have been introduced and shows that 

 the average crest height may be conveniently measured from water level 

 records made with slow chart speed. The crest height measurements were 

 made to one-quarter of the smallest division on the test record. Depend- 

 ing on calibration constant, this quarter division equaled 0.001 to 0.006 

 foot fO.03 to 0.18 centimeter). 



SWL 



Figure 5. Water level record and measured wave dimensions: 



Wave height, H, crest height, W, and trough depth, Q. 



