b. The renourishment factor (Rj) compares the stability of borrow 

 sediments relative to native beach sediments by estimating how often renour- 

 ishment may be required. 



2. Both beach-fill models use the mean and sorting values of the com- 

 posite grain-size distributions of native and borrow sediments as basic 

 input . 



3. A composite distribution describes the overall, or averaged grain- 

 size characteristics of sediments sampled from a particular beach or borrow 

 site deposit. 



a. For a beach, surface samples should be collected from the 

 active profile surface in accordance with a sampling plan designed to ade- 

 quately assess the along-beach, across-beach, and seasonal components of 

 textural variability. 



b. Sediment samples obtained from cores rather than surface sam- 

 ples are usually used to evaluate the composite texture of a borrow source 

 and to estimate the potential volume of suitable sand in the body. 



c. The best composite distributions are obtained by either averag- 

 ing the percentage of sediment in each size class interval for all samples 

 collected, or by analyzing the gsd of a sample obtained by mixing equal 

 amounts of the individual samples. Both methods should provide identical 

 results. 



d. Careful attention should be paid to the design of sediment sam- 

 pling plans since the quality of any beach-fill calculations is, at best, 

 only as good as the native beach and borrow composites. 



4. Sediment analysis considerations. 



a. For beach-fill purposes, particle size is expressed in phi 

 units and the phi mean and phi sorting are used to describe sedimentary 

 gsd. 



b. It is best to use a constant phi interval for describing 

 particle-size distributions and for most purposes, an interval of one-half 

 phi is adequate. 



c. Sediment-size analyses can be obtained using either sieving or 

 settling techniques; however, sieving data are probably more reliable. 



d. It is important not to mix sieving and settling data because 

 each method reflects different properties of the sedimentary particle and 

 conversion equations are not too powerful. 



e. If the mixing method is used to obtain a single composite sam- 

 ple, care must be taken in the laboratory to obtain random splits of appro- 

 priate size from individual samples and then to mix these splits completely 

 to eliminate bias in selecting the final sample of the mixture to be 

 analyzed. 



41 



