a total of 549 different measured profile changes. Though no hurricanes or 

 100-year events are included, it is a unique data set with which to examine 

 natural variability in profile change. 



35. Each case was specifically selected from a larger group of surveys 

 to isolate the effects of single storms. Because all poststorm surveys were 

 conducted within 9 days of the storm, the data contain minimal effects of 

 poststorm beach recovery. For each case, shoreline and volume changes 

 relative to mean sea level (MSL) are computed and presented for a number of 

 beach profile lines.* Birkemeier, Savage, and Leffler (in preparation) also 

 report volume changes based on half-meter contours of elevation. Because the 

 present study is concerned with erosion above the surge level (including the 

 astronomical tide), these data were used to compute the volume changes above 

 the peak measured water level. 



36. Also included in Table 1 is the wave height and water level infor- 

 mation associated with each storm. The wave data were hindcast according to 

 Jensen (1983). Water level measurements were obtained from nearby tide 

 gages. The peak levels given in Table 1 were computed relative to MSL. Note 

 that because the water level data were not obtained at each beach, a true 

 measure of the local surge and the volume change above the surge level is not 

 available . 



Shoreline position 



37. A usual measurement of profile change is the change in shoreline 

 position, which is defined as the MSL intercept. Birkemeier, Savage, and 

 Leffler (in preparation) have found that generally both the MSL shoreline 

 position and the beach slope at MSL are relatively insensitive to storm 

 changes, regardless of locality or storm. For example, of the 549 profile- 

 survey combinations for which an MSL shoreline change could be computed, 81 

 percent eroded based on volumetric changes (regardless of magnitude); whereas 

 only 54 percent of the lines had erosional shorelines. Although poststorm 

 recovery (which would affect the shoreline position) is certainly a factor on 

 the 46 percent of the lines which showed shoreline accretion, there is 



* The datum used by Birkemeier, Savage, and Leffler (in preparation) is the 

 National Geodetic Vertical Datum (NGVD) of 1929 which is commonly equated to 



MSL. Since MSL implies a physical land/sea interface, it will be used in 

 place of NGVD. 



19 



