typical of design conditions (storms with return periods of 50 to 100 

 years) . 



Various methods have been presented by Edelman (1968), Vallianos (1974), 

 and Dean (1976) for estimating storm erosion. These methods relate dune 

 recession to storm tide based on the equilibrium profile concept and a balance 

 of eroded and deposited material. Storm duration and the development of an 

 offshore bar are not included. These are important factors since few storms 

 last long enough for the profile to reach a new equilibrium shape, and the 

 presence of an offshore bar either before the storm or the creation of one 

 during the storm can significantly affect the storm's impact on the beach by 

 causing waves to break offshore and to dissipate much of their energy before 

 reaching the beach (Dean, 1976). Hughes and Chiu (1981) present a method for 

 estimating storm changes based on model tests which attempt to recreate the 

 measured effects of Hurricane Eloise on the Florida coast. Their procedure, 

 which requires field verification, recognizes the importance of the offshore 

 bar. 



Lacking satisfactory means for predicting profile changes, the engineer 

 must estimate them using published representative changes measured for similar 

 areas. Long-term and storm profile changes for a number of Great Lakes and 

 east coast areas are documented in DeWall et al. (1977), DeWall (1979), Everts 

 et al. (1980), Miller et al. (1980), Kana (1977), and Birkemeier (1981). 



Table 4-6 tabulates the effect of a number of storms along the Atlantic 

 and gulf coasts of the United States (Fig. 4-31). Columns are included 

 detailing both the storm (columns 5-8) and the beach changes which occurred 

 (columns 9-13). Generally, the table includes only storms for which the 

 prestorm and poststorm surveys were done reasonably close to the date of the 

 storm. This is particularly important for the poststorm survey since 

 significant beach recovery can occur in the waning stages of a storm 

 (Birkemeier, 1979; Kana, 1977). 



For consistency, wave data from the Phase III east coast wave hindcast 

 model of the Waterways Experiment Station calculated in 9.1 meters (30 feet) 

 of water have been used. The recurrence interval has also been computed using 

 these data from Atlantic City, New Jersey. The storm surges are computed from 

 actual gage records. Note that the actual storm intensity is due to a combin- 

 ation of columns 7 and 8. 



Volumetric losses computed above MSL have been tabulated for each storm 

 and locality in columns 11 and 12. Wide variation in volume losses at single 

 profile lines results from the proximity of structures, inlets, and nearshore 

 bathymetry. Because of this, the median change probably better represents the 

 average rather than the jnean. 



An examination of Table 4-6 provides some insight into the importance of 

 storm surge, storm duration, and wave conditions. The highest surge occurred 

 during Hurricane Eloise in September 1975 and, though it caused erosion over 

 long reaches of coast because of its short duration, the average change was 

 not unlike the data for many of the northeasters. The highest reported surge 

 and the largest changes for a northeast storm were reported by Caldwell 

 (1959). Some of this change may result from the long period between the first 



4-78 



