those commonly measured in laboratory studies^ we utilized measurements of 

 wind velocity (onshore^ offshore, and parallel to shore), angle of wave- 

 front approach (which is not constantly parallel to the shoreline in nature, 

 as it usually is in the laboratory), and tidal-current velocity. Finally, 

 we inserted wave steepness as a variable in the least- squares analysis and 

 ran five lag periods. 



Thus: _ _ _ _ 



Sg = f / (MJs, T, Lo, Ho, Ho/Lo, U^^, U^f, Up, a, h, p, Cjt^_^ 



Results Table 11 presents the resiilts of the first stage of re- 



gression analysis. The highest "jJi-SS-reduction is found at lag period 5;> 

 perhaps because of the dominance of Xk (Hq) and XJ (Uof ) . It is also 

 noted in passing that lag periods 2 and 5^ which show the highest io-SS-re- 

 ductions are lag periods that coincide with times of high tide for 6 of 

 the l8 slope observations used in the analysis. 



Discussion It is seen in table 11 that when the variables are 



considered individually, mean grain size and water density (Xsl and ll) 

 generally have the greatest effect on shoaling-wave zone slope, out-rank- 

 ing the wave parameters considerably. The significantly high effect of 

 (M^)3 on 'S could easily have been predicted from considerations of the 

 mechanics of slope formation and from the known relation between slope 

 and particle size, usually found on foreshore slopes (cf . Bascom, 195l) • 

 A difference exists in the mechanics of alternation of the lower foreshore 

 slope, however, where permeability of the sloping surface assumes con- 

 siderable importance in the process of transportation and deposition. 

 Fluid drag forces are of greater significance to grain movement on the 

 shoaling-wave slope. 



Water density, a factor of unexpected importance, -undoubtedly in- 

 fluences the shoaling-zone slope through its effect on threshold drag 

 velocities and turbulence at the bed. Wave tank experiments on beach slope 

 modification at the Coastal Engineering Research Center, using warm and 

 cold water, have revealed that under constant incoming wave energies the 

 slope modification was more rapid under cold-water conditions- (The final 

 slopes under both conditions were closely similar) . 



The strongest combinations of variables taken six at a time make 

 an interesting study. Referring again to lag periods 2 and 5 (tables B28 

 and B3l), which show the greatest percent reductions in total SS, it is 

 seen that average grain size, wave period, wave steepness and tidal-current 

 velocity, appear in the two combinations of six variables for these lag 

 periods. Absent, but occurring in all of the other strongest combinations 

 of six (tables B27, B29, and B30) is wave height (Xk) , while wind velocity 

 offshore and parallel to shore appears in two of the other combinations. 

 This may be evidence that the slope in this region is shaped by tidal 

 currents in conjunction with wave characteristics at high tide (lag periods 

 2 and 5), but more by wave height and winds during half tides or low tide. 

 More observations for lag periods keyed to times of low tide will be need- 

 ed to settle this point. 



45 



