B21 and B22), it is difficult to assess their true influence. It appears, 

 however, that these variables will logically combine with wave steepness 

 (X5, tables B15 and Bl6) to erode the lower foreshore during falling tide. 

 Variable Xll, water density, will affect the rate of sand-grain transport 

 by fluid drag. The variable D, Xl^, will be of importance in determination 

 of the magnitude of erosion or deposition during rising and falling tides 

 as it affects the infiltration of swashes and the ability of the backwash 

 to transport sand back toward the breaker zone; i.e., the ability to scour 

 the lower foreshore. The significance to net erosion of variable X{ , wind 

 velocity offshore, is believed to lie in three areas: l) in its interlock 

 with a, and V (table B9), noted earlier in the section on longshore- current 

 velocity, 2) in the postulated mechanism whereby offshore wind of suffi- 

 cient magnitude is capable of aiding in the offshore tranport of finer 

 particles thrown into suspension in the breaker zone at the time (lag period 

 2) that high tide covers the lower foreshore, and 3) in its interlock with 

 water density, wherein offshore winds cause denser water to move shoreward 

 in the lower layers, as mentioned in the section treating (j^^) s,' Angle 

 of wave approach, X9, although interlocked to a degree with V, may influence 

 circulation over the lower foreshore at high tide in such a way that rip 

 currents are more effective in removing sand from the foreshore for certain 

 values of a. The rate of rise of the still -water level (X12) is of impor- 

 tance to net foreshore erosion in lag periods 3 and 6, when the tide is 

 rising. The rate of rise and fall (X13, table BI5) of the still water level 

 will determine the time over which any of the other independent variables 

 will be able to act at a given point. 



Table 10 presents the resiilts of the regression analysis for the 

 strongest variables taken six at a time after redundant variables X3 (Lq) 

 and X5 (Hq/Lq) have been removed. If the maximum ^SS-reduction values 

 for lag periods for correlative tide stages are added together, lag periods 

 1 and k, 2 and 5, and 3 and 6 have values of 67. 21, 8^4.82, and 58. 09, re- 

 spectively. Thus, the influence of variables acting about the time of 

 high tide is highest on net erosion of the foreshore, as it is measured in 

 this study. And the four variables most influential at high tide will be 

 (table 10) Sf, Uof, Oi, and D. 



Summary. --Based upon an analysis involving 12 independent variables, 

 it is possible to say that the combination of 5 variables that shows the 

 most influence on net erosion of the lower foreshore is composed of vari- 

 ables Sf, T, Uof, Oi, and D. This combination is most-influential_about 

 the times of high tide. During times of fallling tide, variables S^, T, Hq 

 and a compose the most- influential combination of variables. The rate of 

 rise of the still -water level, depth to the water table, and beach slope 

 are judged to be the most important variables during time of rising tide. 



42 



