12 



Wave hindcasting is a technique widely used for estimating wave statistics 

 by analysis of weather maps using techniques developed from theoretical 

 considerations and empirical data (Shore Protection Manual 1984). The 

 coastal scientist can use published hindcast data or may, at times, choose to 

 compute original estimates in a study of the geologic history of coasts. Over 

 the last several decades since wave hindcasting came into common use, many 

 improvements have been made in the technique, and reliable information on 

 wave climate in given areas can be obtained. Appendix B is a list of the 

 USACE Wave Information Studies reports, which cover the Atlantic, Pacific, 

 Gulf of Mexico, and Great Lakes coasts. Advantages of hindcasting include 

 the long-term database associated with weather maps and the comparatively 

 economic means of obtaining useful information. Disadvantages involve the 

 transformation of waves into shallow water, especially in areas of complex 

 bathymetry or near rivers. 



Visual wave observations from ships at sea and from shore stations along 

 the coasts of the United States are also published in several references. 

 Although observations are less accurate than measured data, experienced 

 persons can achieve reasonably accurate results and the great amount of 

 observations available makes visual wave observation a valuable resource. 

 Offshore, shipboard wave observations have been compiled by the U.S. Navy 

 Oceanographic Research and Development Activity, now the Naval Research 

 Laboratory (NRL), in the form of sea and swell charts and data summaries 

 such as the Summary of Shipboard Meteorological Observations (SSMO). 

 While geographic coverage by these sources is extensive, the greatest amount 

 of observations come from shipping lanes and other areas frequented by ship 

 traffic. 



At the shore, a program sponsored by HQUSACE for data collection is the 

 LEO program (Schneider 1981; Sherlock and Szuwalski 1987). The program, 

 initiated in 1966, makes use of volunteer observers who make daily reports on 

 conditions at specific sites along the coasts of the United States. Data from 

 over 200 observation sites are available from CERC (Figure 5). As shown, 

 LEO data not only include wave parameters, but also information on winds, 

 currents, and some morphologic features. LEO is best applied to a specific 

 site, and does not provide direct information on deepwater statistics. The 

 biggest disadvantage is the subjective nature of the wave height estimates. 

 LEO data should only be used as an indicator of long-term trends, not as a 

 database of absolute values. 



Water Level Data 



Water level information is important for analysis of geologic history over 

 modern process, historic, and geologic time scales (Figure 6). Over modern 

 process time scales, water level changes at the coast include tides, which 

 occur diurnally or semidiurnally, setup and setdown associated with storm 



Chapter 2 Secondary Sources of Coastal Information 



