Measurement of The Independent Variables 



The variables now mentioned (and described in Appendix A) were 

 measured for the analyses of both the increment of net erosion (Jf) and 

 net deposition (Kf ) . 



Slope of the lower foreshore was determined by first passing a smooth 

 curve through the plotted altitudes of the sample stations at which Jf and 

 Kf were determined (fig. 3). A line of mean slope was then passed through 

 this curve by eye^ and_the line's angle with the horizontal was taken as 

 the mean slope angle (Sf) of the "lower foreshore." This angle was rela- 

 tively easy to measure. The two transects (fig. k) provided a good range 

 of slope angles for the regression analysis, although the values were 

 somewhat clustered. Wind, wave, water density, and tide data were assumed 

 constant at both transects. In addition to Sf, only the values for long- 

 shore-current velocity and depth to the water table at the top of the up- 

 rush varied between the two transects. Thus, the following relationship 

 could be postulated: 



Jf or Kf = f (Sf, T, Lo, H^, Hq/Lq, \j^^, ij^f, Up, a, V, p, t]^, ^f, D)^^_g 



where t = a "lag period, " 0-i+ hours long, prior to measurement of the de- 

 pendent variables or prior to another lag period of equal duration. 



Average mean size on the lower-foreshore slope was not included in 

 the analysis because of the considerable data redundancy that would have 

 been introduced. Also, the noise content of such data woiild have been 

 quite high, because grain-size variability is at a maximum when crossing 

 the breaker zone. 



Wet Deposition (jf) 



Results. — Table 7 shows the results of the first stage of the analy- 

 sis, in which the independent variables are studied one at a time. Total 

 •^-SS-reduction values are relatively high, considering the noise content 

 of the variables. The least-squares analysis shows that lag periods 1, k, 

 and 5 have the most influence on net deposition on the lower foreshore. 

 If the total '^-SS-reductions for lag periods for corresponding tide stages 

 are added together, lag periods 1 and U, 2 and 5^ and 3 and 6 have total 

 fo-SS-reduction values of 173-38, 169.85, and 163.27, respectively. Thus, 

 the variables that act during falling tide levels appear to exert a some- 

 what greater influence on foreshore deposition than those acting during 

 the time of rising tide. 



Slope angle of the lower foreshore (Xl) emerges as the most con- 

 sistently important variable, reaching its maximum influence 0-U hours 

 before measurement of Jf. Other less-influential variables show relatively 

 less consistency by lag periods, with the possible exception of wave height 

 (X4), which increases in influence backward in time. The five strongest 

 % SS reductions by independent variables taken in combinations of two to 



36 



