obtained by compass but some were also obtained by measuring the speed of 

 the plunge point of the breaker or by crude triangu lat ion. Wave height (HB) 

 was measured visually or from oscillographs of the water surface. SLOPE 

 was the average slope between the mean water line and a point 6 feet below 

 mean water level. Other data include histograms showing the distribution 

 of some of the measured variables from this CERC field project at Nags Head. 

 THETAB in observation 352 is a single measurement at a time of changing wave 

 conditions. VMEAS in observation 351 was small but not actually zero. Wind 

 speed was high during nearly all the Nags Head measurements. 



5. Discussion of Data 



The data in the tables and the foregoing descriptions indicate 

 differences among the sets of data. Among the laboratory studies, some 

 differences are in the magnitude of the variables tested. For example, 

 the laboratory conditions of Putnam, Munk, and Traylor are for conditions 

 producing high values of VMEAS and THETAB. Of the 225 laboratory observa- 

 tions in the listing, six observations in the data of Putnam, Munk, and 

 Traylor account for the six highest velocities (2.2 to 3.8 ft/sec) and 

 the six highest breaker angles (39° to 3&°). No value of THETAB in their 

 laboratory experiments was less than 10°, but all of Savi lie's data, and 

 most of the measurements of Galvin and Eagleson were for conditions pro- 

 ducing THETAB less than 10°. 



There are also differences in the variables which the investigators 

 chose to measure. In the laboratory experiments of Savi Me and of Brebner 

 and Kamphuis, THETAB and HB were not measured, but THETAO and HO were com- 

 puted from offshore measurements instead. As explained in paragraph 4, 

 the values of THETAB and HB for these two studies were newly computed for 

 this paper; thus they will vary more regularly, yet they may be less accu- 

 rate than actual measurement. 



The experimental conditions of the laboratory tests also differ 

 considerably. No two of the basins were alike in size and layout, and 

 Savi lie's measurements were the only ones made on a deformable sand beach. 



Large differences among the data from the field studies are also evi- 

 dent. The data of Inman and Quinn, although they provide useful statistics 

 on variability, cannot be readily compared with other field measurements 

 because their data are spatial averages along the beach. The data of 

 Moore and Schol I are for lower waves, steeper beaches, and weaker currents 

 than the other field studies. The few observations in the Nags Head study 

 are accompanied by documented uncertainties, many of which were probably 

 present in the other studies as well. Putnam, Munk, and Traylor velocities 

 and Nags Head velocities are, on the average, significantly higher than in 

 the other studies. 



Viewed as a whole, the difference in magnitude between the laboratory 

 and field data is greatest in wave height, and less for wave period and 

 beach slope. Surprisingly, there is little difference between the average 



