IV. OBSERVATIONS AND RESULTS 



A comparison of the monochromatic wave runup data using the runup 

 board-gage and the runup data collected by Saville (1956) and Savage 

 (1958) is shown in Figure 4. In Figure 4, the ratio of the runup divided 

 by the wave height, R/H, is plotted versus the wave height divided by 

 the square of the wave period, H/ T 2. The agreement between sources indi- 

 cates that the gage provides a measure of runup that compares wfell with 

 previous measures. Gage runup values were also consistent with visual 

 runup observations taken simultaneously. 



The differences in the relative runup between sources, shown in Figure 

 4 for values of H/ T 2 less than 0.01, are probably due to the influence of 

 secondary waves (Multer, 1973). Multer noted that secondary waves cause 

 variations in runup that are a function of the distance between the runup 

 slope and the wave blade. The exact distance between the wave blade and 

 slope for the tests conducted by Saville (1956) and Savage (1958) is not 

 known but it was probably different than the distance used in this study. 

 Secondary crests are observed for relatively long waves, i.e., depth to 

 wavelength ratios less than 0.09 (Madsen, Mei, and Savage, 1970), which 

 would include the wave periods of 2.63, 3.65, and 4.70 seconds used in 

 these studies. Most of the wave conditions using the above periods had 

 values of H/j2 less than 0.01 where the runup discrepancies between 

 sources occurred. 



The runup gage records showed that the runup time history had broad, 

 flat crests and short, sharp troughs, a shape similar to a trochoidal wave 

 profile with the crests and troughs reversed. A section of the record for 

 run 8 of Table 3 and the record of the incident wave conditions are shown 

 in Figure 2. For monochromatic waves, the trochoidal shape of the runup 

 record was more evident than for run 8 with irregular waves. 



In comparing wave and runup records, it was found that for some mono- 

 chromatic wave conditions there was not a clearly defined runup crest 

 for every incident wave crest. For a wave period of 0.72 second there was 

 approximately one runup crest for every two wave crests. The ratio of 

 runup crests to wave crests tended to increase as the wave period increased 

 until it reached a ratio of 1, somewhere between periods of 1 and 1.5 

 seconds. There was also a loss of runup crests for irregular waves which 

 was surprisingly great when compared to the loss associated with their 

 monochromatic components. Table 3 gives the ratio of runup crests, N^>, 

 to wave crests N c . Run 3 in Table 3, with a zero up-crossing period of 2 

 seconds, shows a small loss of runup crests which was not evident from 

 visual observations. Inspection of the wave record for run 3 shows a 

 slight perturbation in each of the troughs which was probably caused by 

 wave reflection from the slope, since the period appeared to be too short 

 for secondary waves. This perturbation was large enough (about 1 percent 

 full scale) at one time to be counted as a crest which caused run 3 to have 

 one runup crest less than the number of wave crests. 



