PART VII: SURVEYS 



57. 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 seasonal variations in wave and current conditions. 



58. 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 4.5m 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 chang- 

 ing 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). 



FRF Pier 



Figure 22 . Permanent trough under 

 the FRF pier, 6 September 1990 



49 



