water depth, and tidal-current velocity. This combination of variables 

 exerts its maximum influence on the slope through a lag in time of between 

 k and 8 hours, and apparently to a lesser extent between l6 and 20 hours. 

 This delay may reflect the influence exerted on the slope during the time 

 of the previous two high tides. Wave height, angle of wave approach, and 

 water density become more influential through delays in time amounting to 

 0-k, 8-12, or 12-l6 hours, and coinciding with or approaching times of 

 low tide. 



Average Mean Grain Size in the 



Shoaling-wave Zone (M^)^ 



Variables measured . --The measurements used in this_ analysis were 

 the same ones as were used in the previous analysis for Sg, average mean 

 grain size being interchanged with Sg as the dependent variable. Thus: 



(Mj = f (Sg, T, Lo, Hq, Ho/Lq, Uon, U^f. U . a, h, p, C) 



^ _ ^1-5 



The analysis was run for five periods, as was done for Sg. 



Results . —Table 12 presents the results of the first stage of the 

 analysis where it is seen that the most- influential lag period is number 

 2, which occurs 8-12 hours prior to measurement of the independent variable. 

 Lag periods 2, k, and 5 Sixe of about equal influence, while lag period 1 

 is the least influential. Variable XI is seen to be among the dominate 

 variables when they are taken individually, and this is to be expected in- 

 asmuch as a high interdependence between Sg and (M2)g was noted in the pre- 

 vious analysis. Because of the possible masking influence of this dimen- 

 sionless variable, XI, two sets of tables have been prepared, both of which 

 show the strongest combination of independent variables influencing (M2)g. 

 One set (tables BU7-B51) includes all 12 Xs; the other set (tables B52- 

 B56) does not include XI. Finally, a set of tabl-es for the combination of 

 independent variables showing the weakest influence (tables B57-B6i), and 

 a set of frequency tables (tables b62-B66) have been prepared. 



Discussion Turning to table Bk'^, for lag period 3, one sees that 



the most- influential combination of variables taken six at a time consists 

 of S'g, T, Ho/Lq, Up, OC, and C. Variables H^/Lq, U ,_aiad C also enter into 

 the weakest combination, when they combine with Lq, Uq^., and h (table B59) . 

 Recognizing the importance of slope in its ^influence on particle-sizes 

 transported, we turn our attention to the other variables in this strongest 

 combination of six variables. The reader is reminded that T is redundant 

 with Hq/Lq, through the relationship Lq = 5-12t2, which relationship was 

 used in this study for obtaining Lq. At any rate, the fluid forces at 

 the water- sediment interface that are induced by varying wave periods and 

 wave steepness will tend to move grains of various sizes over the shoaling- 

 zone slope. Superimposed upon this mass transport by the wave-drift cur- 

 rent will be the transport induced by tidal and wind-driven currents. For 

 the bottom slope in question (fig. 3), the major c\;irrent will be the tidal 



48 



