sources. Offshore borrow sites have been used successfully in the construc- 

 tion of major beach restoration projects at Rockaway Beach, New York; Dade 

 County, Florida; Redondo Beach, California; and Harrison County, Mississippi. 



d. Berm E l evation an d Width. Beach berms are formed by the deposit of 

 material by wave action. The height of a berm is related to the cycle change 

 in water level, normal foreshore and nearshore slopes, and the wave climate. 

 Some beaches have no berms; others have one or several. Figure 5-5 illus- 

 trates a beach profile with two berms. The lower berm is the natural or 

 normal berm and is formed by the uprush of normal wave action during the 

 ordinary range of water level fluctuations. The higher berm, or storm berm, 

 is formed by wave action during storm conditions. During most storms, waves 

 and wave setups will cause an increase in the normal water level on the 

 beach. Wave overtopping and backrush with sufficient duration may completely 

 obliterate the natural beach berm. 



Bluff ^ /-Scorm Berm 



or 

 ticorpm»nt% \ Natural Benn ■> 



r 



Beach jeorp -J 



Crtst of barm 



Breokeri 



Ordinorv low wo tar level 



Figure 5-5. Beach berm system. 



The degree of protection to the backshore depends greatly on the effec- 

 tiveness of the storm berm. Beach berms must be carefully considered in the 

 planning of a beach fill. If a beach fill is placed to a height lower than 

 the natural berm crest, a ridge will form along the crest and high water may 

 overtop the berm crest causing ponding and temporary flooding of the backshore 

 area. Such flooding, if undesirable, may be avoided by placing the fill to a 

 height slightly above the natural berm crest elevation. Several alternative 

 techniques may be employed to estimate the height of the berm for design 

 purposes (see Ch. 7, Sec. II). If a beach exists at the site, the natural 

 berm crest height can be measured and future berm elevations can be 

 estimated. An estimate may also be made by comparing the beach profile at the 

 site with beach profiles at sites of similar exposure characteristics (waves 

 and tides) and similar size beach material. If enough wave data applicable to 

 the project site (either developed from synoptic surface weather charts or 

 actual records) are available, wave runup (discussed in Ch. 7, Sec. II) can be 

 estimated to establish a design berm crest height and adjacent beach slope. 



Criteria for specifying berm width depend on several factors. If the 

 purpose of the fill is to restore an eroded beach to protect backshore 

 improvements from major storm damage, the width may be determined as the 

 protective width which has been lost during storms of record plus the minimum 



5-20 



