7 Surveys 



Waves and currents interacting with bottom sediments produce changes in 

 the beach and nearshore bathymetry. These changes can occur very rapidly in 

 response to storms, or slowly as a result of persistent but less forceful sea- 

 sonal variations in wave and current conditions. 



Nearshore bathymetry at the FRF is characterized by regular shore-parallel 

 contours, a moderate slope, and a barred surf zone (usually an outer storm bar 

 in water depths of about 4.5 m and an inner bar in water depths between 1.0 

 and 2.0 m). This pattern is interrupted in the immediate vicinity of the pier 

 where a permanent trough runs under much of the pier, ending in a scour hole 

 where depths can be up to 3.0 m greater than the adjacent bottom (Figure 22). 

 This trough, which apparently is the result of the interaction of waves and 

 currents with the pilings, varies in shape and depth with changing wave and 

 current conditions. The effect of the pier on shore-parallel contours occurs as 

 far as 300 m away, and the shoreline may be affected up to 350 m from the 

 pier (Miller, Birkemeier, and DeWall 1983). 



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FRF Pier 



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46 



Figure 22. Permanent trough under the FRF pier, 

 24 January 1994 



Chapter 7 Surveys 



