samples (subscript s) can be compared with the overall composite (subscript 

 a) in terms of phi sorting on the ordinate and the scaled difference between 

 phi means on the abscissa. These axes are the same as those used to plot 

 overfill ratio curves in the Shore Protection Manual (SPM) (U.S. Army, 

 Corps of Engineers, Coastal Engineering Research Center, 1975, Fig. 5-3) 

 and are used on several other figures in this study. A point falling in 

 the lower right quadrant means that the sample is finer and better sorted 

 than the grand composite; a point in the upper left quadrant shows the 

 sample is coarser grained and more poorly sorted. 



Several trends are apparent in Figure 4. First, samples taken from 

 high on the foreshore (+12 feet) and extending offshore to -30 feet (-9.1 

 meters) mean sea level (MSL) become, as expected, progressively finer 

 grained; the samples are best sorted on the high foreshore and in the mod- 

 erately deep offshore regions. These relationships hold true for samples 

 from both May and November. Secondly, the May (end of winter) samples are 

 generally coarser on the upper foreshore and near offshore parts of the 

 beach than the November samples, but the samples from both months are sim- 

 ilar farther offshore. These relationships are further reflected by the 

 plots of the four range composites where the May plots (M) are coarser and 

 more poorly sorted than the November points (N) , and thirdly, the scatter- 

 ing of the M's and N's show the variability between the ranges. These 

 trends support well-known process-response relationships where coarser and 

 more poorly sorted sediments generally indicate higher energy conditions 

 such as those occurring in the wave -dominated nearshore, or after a stormy 

 winter season. Although these relationships are generally known, it is 

 important that sampling be designed to include these expected variations 

 in texture. For example, the dots on Figure 4 represent composite esti- 

 mates of C which cluster around C because they include samples selected 

 from both May and November. The problem remaining is to determine the 

 magnitude of textural variation contributed by these three components 

 (across profile, along beach, and seasonal) to decide upon the optimum num- 

 ber of samples needed to estimate each component. Table 4 is useful in 

 solving this problem. 



Table 4 shows the phi mean values of the 64 samples from Pt. Mugu used 

 for Figure 4, along with average mean values per profile and per elevation 

 for both May and November, plus grand means, and standard errors of the 

 mean for all profiles and elevations. Table 4 also shows that the greatest 

 variation in grain size occurs at different elevations along the profiles 

 and that little variation occurs between profiles. There is a pronounced 

 size difference between summer (November) and winter (May) . The ranges 

 are so similar for each month sampled that probably only one or two ranges 

 would have been sufficient to characterize this beach which is fairly con- 

 sistent along its length in terms of width, slope, and offshore topography. 

 A plan for additional sampling might call for two ranges to be sampled at 

 eight elevations for each season, or current investigations of the depth 

 component of textural variation may indicate that core samples obtained 

 during one season alone will be sufficient to describe the composite char- 

 acter of all sediments actively affected by beach processes. 



19 



