includes all profiles surveyed. The two February 1972 storms at Jones 

 Beach include all profiles away from the influence of inlets, reducing 

 the number of profiles from 15 in the December 1970 storm to 10 in the 

 February 1972 storms. The November 1953 storm gives relatively high 

 storm damage which may partly result from the long time interval between 

 pre-storm survey and the storm. (See Columns 1 and 3.) These results 

 are also affected by the fact that they omit some profiles "believed to 

 be influenced by the presence of a seawall or a bulkhead," (Caldwell, 

 1959, p. 4.) 



Although the data in Table 4-5 are not completely comparable, the 

 results do suggest that the average volume of sand eroded above mean sea 

 level from beaches about 5 or more miles long has a certain range of val- 

 ues. A moderate storm may remove 4 to 10 cubic yards per foot of beach 

 front above MSL; an extreme storm (or a moderate storm that persists for 

 a long time) may remove 10 to 20 cubic yards per foot; rare storms that 

 are most destructive in beach erosion due to a combination of intensity, 

 duration, and orientation may remove 20 to 50 cubic yards per foot. These 

 values are average for beaches 5 to 10 miles or more long, and they are 

 compatible with other, less complete, data for notable storms. (Caldwell, 

 1959; Shuyskiy, 1970; and Harrison and Wagner, 1964.) For comparative 

 purposes, a berm 100 feet wide at an elevation of 10 feet MSL contains 37 

 cubic yards per foot of beach front, a quantity that would be adequate 

 except for extreme storms. 



In terms of horizontal changes rather than the volume changes in 

 Table 4-5, a moderate storm can erode a typical beach 75 to 100 feet or 

 more, and leave it exposed to greater erosion if a second storm follows 

 before the beach has recovered. This possibility should be considered 

 in design and placement of beach fills and other protective measures. 



Extreme values of erosion may be more useful than mean values for 

 design. Column 17 of Table 4-5 suggests that the ratio of the most ero- 

 ded above-MSL-profile to the average profile for east coast beaches ranges 

 from about 1.5 to 6. If the average erosion per profile is based only on 

 those profiles showing net erosion, then this ratio is probably between 

 1.5 and 3. 



Although the dominant result of storms on the above MSL part of 

 beaches is erosion, most post-storm surveys show that the storm produces 

 local accretion as well. Of the 90 profiles from Cape Cod, Massachusetts, 

 to Cape May, New Jersey, surveyed immediately after the December 1970 

 storm, 16 showed net accretion above mean sea level. (Compare Columns 4, 

 11, and 12 in Table 4-5.) Similar results are indicated for a number of 

 more severe storms. (Caldwell, 1959.) 



The storm surveys also show that the shoreline on many beaches may 

 prograde seaward even though the profile as a whole loses volume, or 

 vice versa. This possibility suggests caution in interpreting aerial 

 photos of storm damage. (Everts, 1973.) 



4-74 



