7 Surveys 



Waves and currents interacting with bottom sediments produce changes in 

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

 sponse to storms, or slowly as a result of persistent but less forceful seasonal 

 variations in wave and ciurent 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. 



FRF Pier 



Figure 22. Permanent trough under the FRF pier, 

 25 January 1995 



46 



Chapter 7 Surveys 



