f. Other Factors . Other principal factors affecting littoral processes 

 are the warks of man and activities of organisms native to the particular 

 littoral zone. In engineering design, the effects on littoral processes of 

 construction activities, the resulting structures, and structure maintenance 

 must be considered. This consideration is particularly necessary for a 

 project that may alter the sand budget of the area, such as jetty or groin 

 construction. In addition, biological activity may be important in producing 

 carbonate sands, in reef development, or (through vegetation) in trapping sand 

 on dunes. 



3. Changes in the Littoral Zone . 



Because most vave energy is dissipated in the littoral zone, this zone is 

 where beach changes are most rapid. These changes may be short term due to 

 seasonal changes in wave conditions and to occurrence of intermittent storms 

 separated by intervals of low waves, or long term due to an overall imbalance 

 between the added and eroded sand. Short-term changes are apparent in the 

 temporary redistribution of sand across the profile (Fig. 4-1); long-term 

 changes are apparent in the more nearly permanent shift of the shoreline (see 

 Figs. 4-3, 4-4, and 4-5). 



Maximum seasonal or storm-induced changes across a profile, such as those 

 shown in Figure 4-1, are typically on the order of a few meters vertically and 

 from 3 to 30 meters (10 to 100 feet) horizontally (see Table 4-1). Only 

 during extreme storms, or where the available sand supply is restricted, do 

 unusual changes occur over a short period. 



Typical seasonal changes on southern California beaches are shown in Table 

 4-1 (Shepard, 1950). These data show greater changes than are typical of 

 Atlantic coast beaches (Urban and Calvin, 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 

 shov« 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 erosion of 

 the beach (above MSL) can amount to 5 to 24 cubic meters per kilometer (10,000 

 to 50,000 cubic yards per mile) of shoreline during storms having a recurrence 

 interval of about once a year (DeWall, Pritchett, and Galvin, 1971; Shuyskiy, 

 1970). While impressive in aggregate, such sediment transport is minor 

 compared to longshore transport of sediment. Longshore transport rates may be 

 greater than 765,000 cubic meters (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 meters per year in horizontal 

 motion of the shoreline, except in localities particularly exposed to erosion, 

 such as near inlets or capes. Figure 4-4 indicates that shorelines can be 

 stable for a long time. It should be noted that the eroding, stable, and 

 accreting beaches shown in Figures 4-3, 4-4, and 4-5 are on the same barrier 

 island within a few kilometers of each other. 



4-6 



