b. Beach Recovery . The typical beach profile left by a severe storm 

 is a simple, con cave -upward curve extending seaward to low tide level or 

 below, (See top of Figure 4-26.) The sand that has been eroded from the 

 beach is deposited mostly as a ramp or bar in the surf zone that exists at 

 the time of the storm. Immediately after the storm, beach repair begins 

 by a process that has been documented in detail, (e.g., Hayes, 1971; Davis, 

 et al., 1972; Davis and Fox, 1972; and Sonu and van Beek, 1971.) Sand that 

 has been deposited seaward of the shoreline during the storm begins moving 

 landward as a sandbar with a gently sloping seaward face and a steeper land- 

 ward face. (See Figure 4-26.) These bars have associated lows (riinnels) 

 on the landward side and occasional drainage gullies across them. (King, 

 1972, p. 339.) These systems are characteristic of post-storm beach accre- 

 tion under a wide range of wave, tide, and sediment conditions. (Davis, 

 et al., 1972.) They are sometimes called ridge -and- runnel systems. 



The processes of accretion occur as follows. Sand is transported 

 landward over the nearly flat seaward face of the bar by the waves. At 

 the bar crest, the sand avalanches down the landward slip face. If the 

 process continues long enough, the bar reaches the landward limit of 

 storm erosion where it is "welded" onto the beach. (e.g. Davis, et al., 

 1972.) Further accretion continues by adding layers of sand to the top 

 of the bar which, by then, is a part of the beach. (See Figure 4-27.) 



Berms may form immediately on a post-storm profile without an inter- 

 vening bar-and-trough, but the mode of berm accretion is quite similar 

 to the mode of bar-and-trough growth. Accretion occurs both by addition 

 of sand laminae to the beach face (analogous to accretion on the seaward- 

 dipping top of the bar in the bar-and-trough) and by addition of sand on 

 the slight landward slope of the berm surface when waves carrying sedi- 

 ment overtop the berm crest (analogous to accretion on the landward dip- 

 ping slip face of the bar). This process of berm accretion is also illus- 

 trated in Figure 4-1. 



The rate at which the berm builds up or the bar migrates landward to 

 weld onto the beach varies greatly, apparently in response to: wave con- 

 ditions, beach slope, grain size, and the length of time the waves work 

 on the bars. (Hayes, 1971.) Compare the slow rate of accretion at Crane 

 Beach in Figure 4-26 (mean tidal range 9 feet, spring range 13 feet) with 

 the rapid accretion on the Lake Michigan shore in Figure 4-2 7 (tidal range 

 less than 0.25 foot). 



Post-storm studies by CERC show that the rate of post-storm replenish- 

 ment by bar migration and berm building is usually rapid immediately after 

 the storm. T^his rapid buildup is important in evaluating the effect of 

 severe storms because (unless surveys are made within hours after the 

 storm) the true extent of erosion during the storm is likely to be ob- 

 scured by the post-storm recovery. Lack of surveys before the start of 



post-storm recovery may explain some survey data that show MSL accretion 

 on profiles that have lost volume. 



4-75 



