calculation procedures for changes in shoreline location (e.g., Bruin, 1962; 

 LeMehaute and Soldate, 1980) and must be considered in the design of nearshore 

 structures, subaqueous beach nourishment, and offshore borrow or disposal 

 operations. 



Detailed studies at certain sites have established that appreciable sedi- 

 ment transport by waves on exposed coasts is usually restricted to water 

 depths shallower than 5 to 20 meters (e.g., Dietz and Fairbridge, 1968; Duane, 

 1976; Gordon and Roy, 1977). The seaward limit to vigorous transport must be 

 related fundamentally to sediment and wave characteristics for a site. 

 Despite the absence of a dependable treatment of onshore-offshore transport 

 rates, several useful techniques exist for estimating the seaward limit of 

 significant transport without detailed investigation of nearshore processes at 

 specific sites. 



(1) Variations in Sediment Characteristics . At many localities, a 

 distinct break has been documented in surface sediment characteristics along 

 the shore-normal profile of the inner continental shelf. Traversing the 

 profile seaward, usual nearshore sediments exhibit seaward fining toward very 

 fine, well-sorted sand, then abut sediment which is commonly less well sorted 

 and somewhat coarser (Fig. 4-28). This break in sediment characteristics is 

 interpreted as a boundary between littoral and shelf sediments, with signifi- 

 cant wave agitation and transport restricted to littoral sediments. 



The characteristic shelf sediment for a particular locality depends on 

 local wave climate (Hayes, 1967b) and on other factors affecting sediments 

 supplied to the shelf (Milliman, Pilkey, and Ross, 1972), so that different 

 breaks in surface sediment characteristics may occur. Various interpretable 

 breaks have been reported: sand shape (Bradley, 1958), sand color (Chapman, 

 1981), sediment size change from sand to silt (McCave, 1971), and carbonate 

 content of sediment (Davies, 1974). Uncertainties connected with inter- 

 pretation of surface sediment characteristics include (a) the timespan and 

 type of wave effect indicated at a certain site and (b) how possible disagree- 

 ments betwen various indicators are to be resolved. 



Examination of vertical sedimentary sequences in the nearshore region 

 permits more definitive interpretation of depositional processes and intensity 

 of sediment transport (e.g., Clifton, Hunter, and Phillips, 1971; Hunter, 

 Clifton, and Phillips, 1979). An example demonstrating the value of 

 comprehensive sediment studies is the results (shown in Figure 4-30) from 

 intensive coring on a high-energy and on a low-energy nearshore region (Howard 

 and Reineck, 1981) . The physical and biogenic sedimentary structures revealed 

 comparable process-related bedding sequences at the two sites, with the extent 

 of distinct zones showing a direct response to wave energy. Three zones below 

 MLW were recognized at each site. 



In Figure 4-30, the shoreface (or littoral) zone extends to water depths 

 of 9 meters (MLW) at Point Mugu, California, and 2 meters (MLW) at Sapelo 

 Island, Georgia; this zone is very low in bioturbation, except for a region of 

 sand dollar activity between 6 and 9 meters (MLW) at the California site. 

 Grain size decreases in the seaward direction at each site, but this trend is 

 interrupted in the low-energy environment by the occurrence of original 

 ("palimpsest") sediments beyond a water depth of 10 meters; at the high-energy 

 site, no break in sediment activity or bedding type was revealed by sediment 



4-71 



