Lag Period 

 Number 



Hours Prior To 

 Measurement Of 

 Jf or K^ 



Tide Stage 



0-k 

 k-8 



8-12 



12-16 

 16-20 



20 -2U 



Falling (LW at hrs) 



Rising and falling about HW 

 (HW at 6.12 hrs) 



Rising 



Low(L¥ at 12.25 brs) 



Falling 



Rising and falling about HW 

 (m at 18.37 hrs) 



Rising 



Low (LW at 2U.5 hrs) 



The interval of two tidal cycles duration was chosen for convenience only, 

 as it is far easier to measure the dependent variable in daylight hours 

 than at night. It is true, however, that the single tidal cycle is the 

 more basic dynamic unit and is preferable to the two-cycle interval. Thus, 

 a small amount of erosion of the foreshore might occur dioring the first 

 tidal cycle under one set of independent variables only to be followed by 

 a greater amount of deposition during the second tidal cycle under a dif- 

 ferent set of independent variables. The dependent variable, however, 

 would be measured as an increment of deposition and it would be impossible 

 to realistically interpret the correlation between the set of independent 

 variables that resulted in erosion aad the dependent variable that showed 

 deposition. Alternatively, a large amount of deposition might occur dur- 

 ing the first tidal cycle, and a lesser amount of erosion during the second 

 cycle. Misinterpretations could again arise. 



The difficulties just mentioned are believed to be rather minimal 

 in the data set used for the regression analyses. The values for Jf and 

 Kf usually occur in runs of two to seven successive days. The inference 

 is that Jf and K^ values for intermediate low-tide times would have shown 

 similar tendencies of net erosion and deposition to those at the actual 

 measurement times. For a number of reasons, then, the data sets used in 

 evaluating Jf and Kf are relatively noisy. This will generally be the 

 case when part of the work is done in the breaker zone and times of measure- 

 ment are not keyed to successive times of low tide. 



35 



