The values in Table 20 were also used to calculate James' (1974) 

 renourishment factor, Rj=1.9. This factor expresses the ratio of 

 the retreat rate of the beach after fill placement to the retreat rate 

 before beach-fill operations. However, in its derivation, James (1974) 

 assumed that the postfill retreat rate was linear and not exponential. 

 Therefore, its value cannot be compared to the results of this study. 



The relative changes in the upper beach- face angle (from MHW to MLW) 

 after fill placement were measured for profile WB17. Figure 44 shows 

 that immediately after placement the average beach face angle was 1 on 

 57, which was flatter than the prefill angle of 1 on 35. The beach 

 angle changed fairly rapidly during the first 6 months after placement, 

 and after 9 to 12 months, the difference in the average beach angle at 

 that time and the long-term beach face angle was less than the expected 

 difference due to seasonal fluctuations. It is apparent that a signifi- 

 cant proportion of the upper beach slope adjustments and sorting losses 

 occurred during the first 9 to 12 months. After that period, the upper 

 beach face retreated with a fairly constant slope. 



The value of the exponential decay constant, determined from the 

 average of the individual k values for each of the MLW, MSL, and MHW 

 excursion plots from each profile, was k=0.66. Substituting this value 

 into equation (4), together with £=0.8 and S t =0.95^f^, gave t£=1.8 years: 

 i.e., effectively all initial losses due to sorting, slope adjustment, 

 and lateral spreading occurred during the first 1.8 years after fill 

 completion. Substituting k=0.66, £=0.8, and E t =0 into equation (6) 

 produces t=4.06 years. This means that the beach face eroded back to 

 its original prefill position 4.06 years after fill completion, and that 

 the beach-fill project effectively "bought" this time for the beach 

 segment within the project boundaries by artificially placing sand on 

 the beach. This is in agreement with observed behavior. Between 

 October 1970 and December 1974, an estimated 91 percent of the initial 

 beach fill was lost (U.S. Army Engineer District, Wilmington, 1977), and 

 the sequential beach profiles in Appendix F show that by April 1974 the 

 location of profile WB15 was approximately in its pre-1970 beach-fill 

 position. Only a few percent of the initial fill was retained above the 

 MHW contour after 4 years and, unfortunately, little information is 

 available to describe the changes in offshore bathymetry. Downdrift 

 beaches benefited from the fill due to alongshore transport away from 

 the fill site. However, quantification of this benefit was not possible 

 due to the masking effect of the seasonal variations in beach position. 



Assuming that only slope and sorting adjustments occurred during the 

 first 9 to 12 months, then solving equation (4) for S t at t^=0.75 

 and t2=1.0 indicates that 54 to 62 percent of the total initial fill 

 volume was lost to sorting and slope adjustment. This range compares 

 favorably with the values of 60 to 66 percent sorting loss estimated by 

 the adjusted fill factor and critical ratio techniques, respectively. 



The rate of initial loss of beach material was not constant along 

 the length of the beach-fill project. The k values calculated for 



85 



