Until these improvements can be incorporated, the results of this 

 study indicate that the additional expenses incurred due to the use of a 

 large number of wave rays and high resolution in the bathymetric data 

 cannot be justified. 



Sediment budgets were developed for Wrightsville and Carolina 

 Beaches. These two beaches were each divided into three littoral cells 

 in which the response of the beach to all natural and man- influenced 

 changes was fairly similar. Long-term volumetric changes were assumed 

 to be the result of differences in longshore sediment transport rates, 

 sediment loss to wave overtopping, and to sea level rise. Losses due to 

 ongoing sorting of beach sediment were considered minor. Values of wave 

 energy flux at each cell boundary were multiplied by the empirical 

 factor (3 which relates the longshore transport potential to the long- 

 shore component of wave energy flux. An additional efficiency factor, a 

 which relates the actual volume of sediment transported to the potential 

 amount as predicted from the energy flux analysis, was included in the 

 sediment budget equations. The value of a along a smooth and uninter- 

 rupted coastline was assumed to be one and at positions where a coastal 

 structure (e.g., the north jetty weir at Masonboro Inlet) or where 

 geologic control (availability of sediment supply) prohibit transport, 

 the value of a was assumed to be zero. The solution of the sediment 

 transport equations resulted in a values which indicated that only 

 two-thirds of the gross southerly transport along Wrightsville Beach 

 spills over the north jetty weir into Masonboro Inlet and one-third is 

 either trapped along the southern end of Wrightsville Beach or locally 

 transported northward by wave energy reversals. At the northern ends of 

 Wrightsville and Carolina Beaches, only 10 and 31 percent of the 

 potential volume of sediment is transported out of Mason and Carolina 

 Beach Inlets, respectively. If better volumetric change data had been 

 available for Masonboro Beach, then the influence of Masonboro and 

 Carolina Beach Inlets in terms of their inlet trapping potential on the 

 supply and storage of sand have been determined. 



Analyses of the beach profiles taken along Wrightsville Beach after 

 the 1970 beach fill indicate several components of beach response. The 

 first component was a long-term loss rate of -3.8 meters per year which 

 was approximately equal to the long-term loss rate during the 5-year 

 period prior to the 1970 fill operations. This rate was much higher in 

 the immediate vicinity of the fill than along adjacent beaches both 

 during the prefill and postfill periods, and indicated that the fill 

 placement did not reduce or eliminate the problem which resulted in the 

 need for a fill, but rather provided recreational opportunity and "bough t- 

 time" for the properties behind the project boundaries. 



In addition to the long-term component, an exponential loss of 

 beach-fill volume was recorded during the first 1.5 to 2 years. Excur- 

 sion plot analysis showed that about 80 percent of the total initial 

 fill was eroded during this period of rapid initial loss, and that 

 severe storm erosion was not the primary cause for the very high initial 

 loss rate. 



The first set of profile measurements taken after fill completion 

 indicated that the fill material was placed at a beach angle shallower 



94 



