than are typical of Atlantic coast beaches. (Urban and Galvin, 1969; 

 Zeigler and Tuttle, 1961.) Available data indicate that the greatest 

 changes on the profile are in the position of the beach face and of the 

 longshore bar - two relatively mobile elements of the profile. Beaches 

 change in plan view as well. Figure 4-6 shows the change in shoreline 

 position at seven east coast localities as a function of time between 

 autumn 1962 and spring 1967. 



Comparison of beach profiles before and after storms suggests ero- 

 sion of the beach above MSL from 10,000 to 50,000 cubic yards per mile 

 of shoreline during storms expected to recur about once a year. (DeWall, 

 et al., 1971; and Shuyskiy, 1970.) While impressive in aggregate, such 

 sediment transport is minor compared to longshore transport of sediment. 

 Longshore transport rates may be greater than 1 million cubic yards per 

 year. 



The long-term changes shown in Figures 4-3, 4-4, and 4-5 illustrate 

 shorelines of erosion, accretion, and stability. Long-term erosion or 

 accretion rates are rarely more than a few feet per year in horizontal 

 motion of the shoreline, except in localities particularly exposed to 

 erosion, such as near inlets or capes. Figure 4-5 indicates that shore- 

 lines can be stable for a long time. It should be noted that the erod- 

 ing, accreting, and stable beaches shown in Figures 4-3, 4-4, and 4-5 

 are on the same barrier island within a few miles of each other. 



Net longshore transport rates along ocean beaches range from near 

 zero to 1 million cubic yards per year, but are typically 100,000 to 

 500,000 cubic yards per year. Such quantities, if removed from a 10- to 

 20-mile stretch of beach year after year, would result in severe erosion 

 problems. The fact that many beaches have high rates of longshore trans- 

 port without unusually severe erosion suggests that an equilibrium condi- 

 tion exists on these beaches, in which the material eroded is balanced by 

 the material supplied; or in which seasonal reversals of littoral trans- 

 port replace material previously removed. 



4.2 LITTORAL MATERIALS 



Littoral materials are the solid materials (mainly sedimentary) in 

 the littoral zone on which the waves and currents act. 



4.21 CLASSIFICATION 



The characteristics of the littoral materials are a primary input 

 to any coastal engineering design. Median grain size is the most fre- 

 quently used design characteristic. 



4.211 Size and Size Parameters . Littoral materials are classified by 

 grain size into clay, silt, sand, gravel, cobble, and boulder. Several 

 size classifications exist, of which two, the Unified Soil Classification, 

 (based on the Casagrande Classification) and the Wentworth Classification, 

 are most commonly used in coastal engineering. (See Figure 4-7.) The 



