Table 5-1. Relationships of phi means and phi standard deviations of native 

 material and borrow material. 



determining initial quantities of beach fill, and Figure 5-4 for determining 

 how often renourishment may be required. 



The renourishment and fill factors are not mathematically related to one 

 another. Each relationship results from unique models of predicted beach-fill 

 behavior which are computationally dissimilar although both use the comparison 

 of native and borrow sand texture as input. Nevertheless, the models address 

 the different problems in determining nourishment requirements when fill that 

 is dissimilar to native sediments is to be used (fill factor) and in predict- 

 ing how quickly a particular fill will erode (renourishment). For design 

 purposes, the fill factor, R^ , or its equivalent, should be applied to 

 adjust both initial and renourishment volumes (see Table 5-2). The renourish- 

 ment factor, Rj , should be considered an independent evaluation of when 

 renourishment will be required. Both models are simplistic descriptions of 

 complex beach relationships, and there will be cases where the R. and R, 

 values calculated for a particular borrow material suggest quite different 

 responses from that material. One example is where the models suggest both 

 that overage is required and that the borrow will erode much slower than 

 native beach sediments. This situation could arise with coarser and more 

 poorly sorted borrow sand where early winnowing would remove the overage vol- 

 ume of unstable finer sizes and leave a coarser-than-native sand that erodes 

 slowly. For cases like this and in all cases where these models are applied, 

 engineering judgment and experience must accompany design application. 



5-13 



