22 



data are often useful for characterizing significant environmental processes and 

 responses, such as the effects of severe storms on coastlines. 



Information from secondary sources may be pertinent to studies from mod- 

 ern to paleoenvironmental time scales. Although some geologic data can be 

 compiled from secondary sources, generally it is necessary to conduct original 

 data collection programs using field instruments and observations. This must 

 be followed up by laboratory and office analyses and interpretation. Published 

 data are available from agencies such as the USGS, the U.S. Soil Conserva- 

 tion Service, the American Geological Institute, and CERC. Additional 

 sources of geologic and sedimentologic data in the United States are listed in 

 Chu, Lund, and Camfield (1987). 



Sources of Aerial Photography 



Historic and recent aerial photographs provide invaluable data for the inter- 

 pretation of geologic and geomorphic history. The photographs can be 

 obtained from Federal and state government agencies such as the USGS, the 

 U.S. Department of Agriculture, the EROS Data Center, and others listed in 

 Appendices C and D. Stereographic pairs with overlap of 60 percent are 

 often available, allowing very detailed information to be obtained using photo- 

 grammetric techniques. Temporal coverage for the United States is available 

 from the 1930's to present for most locations. The types of analysis and 

 interpretation that can be performed depend in part on the scale of the 

 photographs, the resolution, and the percentage of cloud cover. The effects of 

 major events can be documented by aerial photography because the photo- 

 graphic equipment and airplane can be rapidly mobilized. By such means, the 

 capability exists for extensive coverage in a short time and for surveillance of 

 areas that are not readily accessible from the ground. 



For modern process studies, a series of aerial photographs provides signifi- 

 cant data for examining a variety of problems. Information pertinent to 

 environmental mapping and classification such as the nature of coastal 

 landforms and materials, the presence of engineering structures, the effects of 

 recent storms, the locations of rip currents, the character of wave shoaling, 

 and the growth of spits and other coastal features can be examined on aerial 

 photographs. For the assessment of some morphologic features, photogram- 

 metric techniques may be helpful. If possible, it is generally considered pref- 

 erable to arrange flights or obtain photography acquired during low tide, so 

 that nearshore features will be exposed or partly visible through the water. 



For studies over historical time scales, multiple time series of aerial photo- 

 graphs are required. Historical photography and maps are an integral com- 

 ponent of shoreline change assessments. Water level and, therefore, shoreline 

 locations show great variation according to when aerial photographic missions 

 were flown. Therefore, the coastal scientist should account for such 



Chapter 2 Secondary Sources of Coastal Information 



