Wind, tide, and most wave measiarements were made every two hoiirs, 

 "both day and night. Some of the other variables listed in table 1 {B^, 

 D, E-u, a., and p) were measured four times a day at O7OO, 1100, 15OO, and 

 1900 hours. (Values at 2300 and 03OO hours were arrived at by linear 

 interpolation-) The variables J^, K^., (^2)3^? S^, and S were usually 

 measured once each day at low tide, while t^)s and S were measiored 

 every k hours d^uring the February field period. 



Approach 



Designation of "cause" and "effect", or "stimiilus" and "response", 

 is rather arbitrary in a system of complexly interlocked variables (like 

 those of table l), all of which may vary simultaneously. In a general 

 way it is possible to say that relationships between the variables in a 

 specific beach environment are conditioned by the natural ranges in 

 magnitude of the variables and by their natural frequencies of occurrence. 

 Ranges in the magnitude of wave height, tidal-current velocity, wind 

 velocity in various diections, and grain size distribution in the various 

 littoral zones are all characteristic for a given beach. Also character- 

 istic are the frequency of occurrence of waves of a given height, currents 

 of a given velocity, and so on. 



Ideally then, to understand the interaction of a variable singled 

 out as an "effect" with a number of other variables designated as "causes", 

 one must measure both "causes" and "effects" over the range of values 

 that they assume in the study area. Understanding of erosion of the 

 foreshore of a beach as it is "caused" by winds, and currents, for example, 

 can come only when foreshore slope, wind velocity, wave height, longshore- 

 current velocity, etc., are measured through their expectable range of 

 values and over a long enough time period so that adequate representations 

 of natural frequencies are obtained. 



It is to be noted that consideration must be given to the fact that 

 the moment of maximum interaction of an effect with its several causes may 

 be influenced by a time delay . The well-documented delay in the response 

 of laboratory beach slopes to unvarying wave trains in wave-tank experi- 

 mentation is a good example of the delay factor in this cause-and-effect 

 relationship. 



It is also to be noted that a given variable designated as an 

 "effect" in the beach-ocean-atmosphere system may in fact be little in- 

 fluenced by some of the variables that are considered «as "causes". Wind 

 velocity parallel to the shore taken as an effect, for example, is in- 

 tuitively independent of water density, angle of wave approach, and mean 

 grain size on the foreshore taken as causes. For this reason it becomes 

 intuitively "unprofitable" to investigate wind velocity parallel to the 

 shore as a function of such improbable causes. Where it appears, however, 

 that one of the measured variables is significantly dependent upon most 

 of the other measured variables, it becomes desirable to investigate 

 that inferred dependency. 



