c. Structure configurations and other engineering activities. 



d. Beach profiles. 



e. Boundary conditions. 



The other data listed in Table 2 are needed for interpretation of sediment 

 transport processes and beach change. For example, coastal subsidence or an 

 earthquake might produce an apparent trend in shoreline recession unrelated to 

 longshore sand transport or boundary conditions. 



Shoreline position 



61. Shoreline position data can be obtained from shoreline surveys, 

 beach profile surveys, aerial photographs, maps, and nautical charts. 

 Shoreline positions should be referenced to the longshore baseline and values 

 interpolated to longshore grid points so that shoreline positions calculated 

 with GENESIS can be easily compared. The terminology "shoreline position" 

 usually refers to the zero-depth contour with respect to a certain datum, for 

 example, mean sea level (MSL) or to mean lower low water (MLLW) . All shore- 

 line position and bathymetry data for wave refraction modeling should be 

 referenced to the same datum. 



62. Plots of shoreline positions may reveal errors in the data as well 

 as trends in shoreline change. As much as possible, the two surveys defining 

 the calibration and verification intervals should be in the same season to 

 minimize the effect of the seasonal cyclical displacement of the shoreline. 



Offshore waves 



63. It is rare to have adequate wave gage data for a modeling effort. 

 If gage data are not available, hindcasts can be used. The Wave Information 

 Study (WIS) (e.g., Jensen 1983a, b; Jensen, Hubertz , and Payne 1989) provides 

 hindcast estimates of height, period, and direction at intervals along all 

 continental US coasts. Gravens (1988) discusses a methodology for use of WIS 

 data in calculation of potential longshore sand transport rates . 



64. At the lowest level of effort, statistical summaries of hindcasts 

 can be used. In typical design mode shoreline change modeling projects per- 

 formed at CERC, offshore wave data are input at 6-hr intervals over the 

 simulation period. Actual wave height in the time series is used, but wave 

 period and direction are grouped into approximately 50 to 100 categories or 



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