geologic history of the coast, the when, how, and of what it was formed, also 

 provides important background material. 



Water level 



76. If the tidal range is large, wave refraction and breaking will vary 

 significantly according to the water level. For micro- and mesotidal coasts, 

 use of either the MSL or MLLW datums (either of which appears on NOAA bathy- 

 metric charts) is considered sufficient. If the tide variation is appreci- 

 able, refraction simulations with different water levels may be necessary. 

 Water level also plays a role in wave overtopping and transmission through 

 breakwaters, sediment overtopping and bypassing (shoreward and seaward) at 

 groins, and interpretation of shoreline position from aerial photographs. 



77. Version 2 of GENESIS does not allow direct representation of tidal 

 change. However, changes in breaking waves as caused by variations in water 

 level can be represented in the wave input. 



Extreme events 



78. The aim of shoreline modeling is to simulate long-term change in 

 shoreline position; effects of extreme events are assumed to be accounted for 

 in the verification process. An extreme event is a natural process or 

 engineering activity that causes a substantial, perhaps irreversible, change 

 in the shoreline position. Without documentation of such events, interpreta- 

 tion of shoreline change could be mistaken. Examples of extreme events are 

 storms of record that greatly erode the beach and dredging during construction 

 of coastal structures. It is possible that one or more extreme events may 

 have dominated shoreline change over the interval between shoreline surveys. 

 This is particularly likely if the calibration or verification intervals are 

 relatively short and an extreme event is bracketed. It is important to have 

 documentation on extreme events so that shoreline and beach processes can be 

 properly interpreted. If possible, time intervals that span known extreme 

 events (including, for example, beach fills of unspecified volume) should be 

 avoided in the calibration/verification process. 



Other 



79. Each site or project brings novel problems, and it is rare that 

 standard operating procedure can be completely followed in a shoreline 



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