for beach-fill material. Ranges of medium values are greater for individual county beaches 

 and their overall size is finer than for sample collections from the shelf or mid-tide samples 

 covering the entire study area. This can be partly attributable to the fact that county beach 

 samples range across the beach from the dune to —30 feet and the offshore samples are 

 usually fine and very fine type F sand (Table 4). The beach samples from the entire 

 shoreUne are biased toward the coarse side since they were collected only from the mid-tide 

 area. Offshore samples are also biased toward the coarse side since selection was based on 

 their appearance as suitable sand for beach nourishment. 



Direct comparison of size data derived from different analysis techniques (settling 

 velocity versus sieve) as in Figure 39 may be made for a general overview. However, 

 comparison of either individual samples or composite values requires that particle-size 

 parameters derived from them be corrected so they are comparable and reproducible by 

 either method. An empirical correction factor for the CERC Rapid Sediment Analyser 

 (RSA) has been determined so that RSA data may be directly equated with sieve data. The 

 equation for conversion is: 



M0 (sieve) = 0.157 + 1.1 M^ (RSA), 

 where 



Mj, (sieve) = the mean sieve diameter, 

 Mj, (RSA) = the mean RSA diameter. 



If only the median diameter is available, an assumption can be made that the median is an 

 approximation to the mean and differences between the two are insignificant. However, the 

 correction factor was determined empirically for the RSA and therefore cannot rehably be 

 used for other settling tube data. 



If differing sets of data are in different units (millimeters and phi), then one set must be 

 converted to conform to the other. It is preferable to transform data to phi (0) values, using 

 the formula: 



= -log^(d^^), 



= diameter in phi units, 



d^ ^ = diameter in millimeters. 



m m 



Data from the native beach (the one to be restored) can be compared directly to data 

 from a potential borrow site by comparison of a composite sample from each area. A 

 composite sample is a single theoretical sample calculated from all samples that statistically 

 represents the spread of mean grain sizes and sorting that is present. Methods of calculating 

 composite values are given by Krumbein (1957). The mean grain size and sorting of the 

 composite samples from the native beach and borrow site can be compared to determine a 



86 



