have been "calibrated" for use with U^ by plotting the field data in Figure 

 4-37 of the SPM using Hg to calculate P^g . The resulting line in Figure 

 4-37 yields equation 4-40 of the SPM: 



Q = (7.5 X lo3) P^g (B-14) 



The 23 field data points used to determine equation (B-14) are shown in 

 Figure 4-37 of the SPM. Nine data points of Watts (1953) and Caldwell (1956) 

 (one of Caldwell's data points is missing from Fig. 4-37 since Q and P^s 

 had opposite signs; see App. C) were reported in terms of significant wave 

 height. Thus, the values for P^g are taken directly from these reports. 

 Similarly, the one data point of Moore and Cole (1960) (not shown in Fig. 4-37 

 since it plots off the scale) is assumed to be in terms of significant wave 

 height, although this is not stated in their report. The 14 data points of 

 Komar (1969), however, are reported in terms of rms wave height and so his 

 values for P^g are multiplied by a factor of 2 before being used in Figure 

 4-37. 



In Figure 4-36 of the SPM, 161 data points from 5 laboratory studies 

 (listed in App. C) are shown in addition to the 25 field data points. In the 

 laboratory studies a train of (relatively) uniform waves was used in each test, 

 so that the wave height measured is approximately equal by definition to the 

 rms wave height. Since the use of the laboratory wave heights gives the 

 theoretical longshore energy flux based on Urms > they were multiplied by a 

 factor of 2 before being used in Figure 4-36 to make them consistent with the 

 energy flux factors plotted for the field data. 



Because it is doubtful that the numerous assumptions relating Hg to Hj^^g 

 are all valid at the same time, the basic relation between Q and Pj^g (eq. 

 B-14) might be considered an empirical relation, calibrated for field use with 

 significant wave height data. The engineering application depends on how well 

 the equations for Pn predict Q when used in equation (B-14) . 



29 



