included in the shoreline location of 24 October. The profile was represented 

 by a straight line from the top of the berm at +8 ft to the depth of closure, 

 -16 ft. Further, the transition was assumed to rotate the profile around its 

 center, i.e., at -4 ft. Geometry then gives the setback associated with a 

 slope change from 1:5 to 1:12 to be 28 ft. This distance was subtracted from 

 the values representing the shoreline of 24 October 1977. 



375. Walker, Clark, and Pope (1980) also report volumetric changes 

 within the project boundaries between the dates of the aerial photographs used 

 here. From October 1977 to October 1978, the project gained approximately 

 4,300 cu yd, whereas from October 1978 to November 1979 about 400 cu yd were 

 lost. Corresponding comparisons were made using the shoreline position files, 

 which indicated a gain of 13,500 cu yd from 1977 to 1978 and a loss of 



6,900 cu yd from 1978 to 1979. Using the 1977 shoreline as a reference, these 

 volume changes convert to an average error of 8.4 ft (1 mm on the aerial 

 photographs) in determination of the 1978 shoreline and an error of 2.7 ft 

 (0.3 mm on aerial photographs) for the 1979 shoreline. To be consistent with 

 previous studies, the 1978 and 1979 shoreline positions were translated 

 forward 8.4 and 2.7 ft, respectively, resulting in volumetric differences of 

 4,260 cu yd from October 1977 to October 1978 and -335 cu yd from October 1978 

 to November 1979. The adjusted measured shoreline positions are shown in 

 Figure 40, and the corresponding SHORL files are given in Appendix D. As seen 

 from Figure 40, the general trend is for erosion along the western part of the 

 study area and accretion in the eastern part. 



376. Figure 41 plots measured volumetric changes within the study area 

 using the October 1977 volume as a reference. The volumetric change varies 

 significantly with season, with a gain of sand over the winter and a loss 

 during the summer. Contrary to what might be expected, the seasonal varia- 

 tions appear to increase in time, rather than approaching an equilibrium. The 

 increase is probably explained by long-term variations in wave climate and 

 water level. Also, there are significant changes in beach volume from year to 

 year, although the general trend is accumulation for the fall and spring 

 measurements, with a least-squares determined value of 2,500 and 



3,500 cu yd/year, respectively. 



159 



