Historical records of shoreline changes are usually in the form of 

 charts, surveyed profiles, dredging reports, beach replenishment reports 

 and aerial photos. As an example of such historical data. Figure 4-52 

 shows the positions of the shoreline at Sandy Hook, New Jersey, during 

 six surveys from 1835 to 1932. Such shoreline changes are useful for 

 computing longshore transport rates. The Corps of Engineers maintains, 

 in its District and Division offices, survey, dredging, and other reports 

 relating to Corps projects. Charts may be obtained from various federal 

 agencies including the Defense Mapping Agency Hydrographic Center, Geolog- 

 ical Survey, National Ocean Survey, and Defense Mapping Agency Topographic 

 Center. A map called "Status of Aerial Photography," which may be obtained 

 from the Map Information Office, Geological Survey, Washington, D.C. 20242, 

 shows the locations and types of aerial photos available for the U.S., and 

 lists the sources from which the photos may be requested. A description of 

 a coastal imagery data bank can be found in the interim report by Szuwalski 

 (1972). 



Other kinds of data usually available are wave, tide, and meteoro- 

 logical data. Chapter 3 discusses wave and water level predictions; Sec- 

 tion 4.3 discusses the effects of waves on the littoral zone; and Sub- 

 section 4.34 presents methods of estimating wave climate and gives pos- 

 sible sources of data. These referenced sections indicate the wave, tide, 

 and storm data necessary to evaluate coastal engineering problems. 



Additional information can be obtained from local newspapers, court- 

 house records, and from area residents. Local people can often identify 

 factors that outsiders may not be aware of, and can also provide quali- 

 titive information on previous coastal engineering efforts in the area 

 and their effects. 



4.812 Interpretation of Shoreline Position . Preliminary interpretation 

 of littoral processes is possible from the position of the shoreline on 

 aerial photos and charts. Stafford (1971) describes a procedure for uti- 

 lizing periodic aerial photographs to estimate coastal erosion. Used in 

 conjunction with charts and topographic maps, this technique may provide 

 quick and fairly accurate estimates of shoreline movement, although the 

 results can be biased by the short-term effects of storms. 



Charts show the coastal exposure of a study site, and since exposure 

 determines the possible directions from which waves reach the coast, expo- 

 sure also determines the most likely direction of longshore transport. 



Direction of longshore transport may also be indicated by the posi- 

 tion of sand accumulation and beach erosion around littoral barriers. A 

 coastal structure in the surf zone may limit or prevent the movement of 

 sand, and the buildup of sediment on one side of the littoral barrier serv- 

 es as an indicator of the net direction of transport. This buildup can be 

 determined from dredging or sand bypassing records or aerial photos. Fig- 

 ure 4-53 shows the accumulation of sand on one side of a jetty. But wave 

 direction and nearshore currents at the time of the photo indicate that 

 transport then was in the opposite direction. Thus, an erroneous conclusion 



4-140 



