notable rapid rearrangement of a profile is by storm waves, especially 

 during storm surge (Section 3.8) which enables the waves to attack at 

 higher elevations on the beach, (see Figure 1-7.) 



The part of the beach washed by runup and runback is the beach face. 

 Under normal conditions, the beach face is contained within the fore- 

 shore, but during storms, the beach face is moved shoreward by the cut- 

 ting action of the waves on the profile. The waves during storms are 

 steeper, and the runback of each wave on the beach face carries away more 

 sand than is brought to the beach by the runup of the next wave. Thus 

 the beach face migrates landward, cutting a scarp into the berm. (See 

 Figure 1-7.) 



In moderate storms, the storm surge and accompanying steep waves will 

 subside before the berm has been significantly eroded. In severe storms, or 

 after a series of moderate storms, the backshore may be completely eroded, 

 after which the waves will begin to erode the coastal dunes, cliffs, or main- 

 land behind the beach. 



The extent of storm erosion depends on wave conditions, storm surge, 

 the stage of the tide and storm duration. 



Potential damage to property behind the beach depends on all these 

 factors and on the volume of sand stored in the beach-dune system when a 

 storm occurs. 



For planning and design purposes, it is useful to know the magnitude 

 of beach erosion to be expected during severe storms. Table 4-5 tabulates 

 the effect of four notable extratropical storms along the Atlantic coast 

 of the U.S. This table provides information on typical observed order-of- 

 magnitude values for beach erosion above mean sea level (MSL) from single 

 storms. 



For the storm of 17 December 1970, information is available from 

 seven localities (Column 2 of Table 4-5). (DeWall, et al. , 1971.) The 

 three other storms include two closely spaced storms affecting Jones Beach, 

 New York, in February 1972 (Everts, 1972), and a storm that affected the 

 northern New Jersey coast in November 1953. (Caldwell, 1959.) Character- 

 istics that distinguish one storm from another are duration and storm 

 surge. (See Columns 9 and 10, Table 4-5.) Storm waves lasted about 1 day 

 for the 17 December 1970 storm, and about 2 days for the other three 

 storms. (See Column 9.) Storm surge elevation varied from a low of 2.8 

 feet to a high of 6 feet in the New York Bight area. The November 1953 

 storm combined longer duration and high storm surge; the 17 December 1970 

 storm had short duration and moderate storm surge; and the February 1972 

 storms both had longer duration, one with moderate storm surge and the 

 other with low storm surge. 



Duration and storm surge (Columns 9 and 10) are consistent with storm 

 damage data (Columns 11 through 16, although the effect is influenced by 

 the choice of profiles included in each study. The December 1970 storm 



4-71 



