5. Longshore Bars . 



The significant variables may be the number, position, and geometry 

 of longshore sandbars. These sandbars may be important in limiting the 

 amount of wave energy reaching the beach by causing waves to break 

 farther offshore, or by affecting the refracted direction of the waves 

 near shore. However, longshore sandbars may explain some of the apparent 

 randomness in time and location of bluff recession. 



Vlll. VOLUME, WIDTH, AND SLOPE DATA 



1 . Estimated Volumes of Erosion . 



The volume of material removed from the dunes or bluffs was estimated 

 during each year of the 2-year study. These values were computed by over- 

 laying the first and last surveys for a study year, locating the inter- 

 section of the beach with the bluff on the first survey, dropping a 

 vertical line from that intersection to the profile of the last survey, 

 and then calculating the volume eroded landward of that vertical line. 

 The resulting volume is shown two-dimensional ly in Figure 25. The 

 composition of the bluff (sand or till) and the volume eroded for each 

 year are shown in Table 6. The pattern of erosion is presented in Section 

 V, Profile Descriptions; volumes calculated range from to 19.9 cubic 

 yards per foot of beach front per year. Data on the size distribution 

 of eroded material were not collected. 



Volume Calculated 



Profile site 3 



First Survey 



Last Survey 



Figure 25. Example of eroded volume computation. 



52 



