History of bottom elevation 



103. A history of the bottom elevations taken at the Baylor wave gage, 



pier end tide gage, and selected other locations along the pier is useful for 



interpretation of data. Variations of 

 elevation under the pier are due to 

 natural beach processes (such as profile 

 changes due to bar movement) , as well 

 as to scour due to the interaction of 

 the pier piles with waves and currents. 

 Figure 39 shows the maximum vertical 

 variation for 1981 as a function of 

 depth. The most active areas were 

 landward of 400 m due to a very mobile 

 nearshore bar. Variations in the scour 

 Q I 2 3 4 hole at the seaward end of the pier 

 Mox. Vert Vor. ( m ) approached 2 m. 



Figure 39. 1981 Maximum ver- „ ^. 



^ - ■, . ^ . J- Bathymetry 



txcal variation of ocean ' ^ 



bottom under FRF pier 104. Beginning in July and at 



approximately monthly intervals thereafter, the bathymetry adjacent to the FRF 

 pier was surveyed. Contour diagrams based on the data for each survey are 

 contained in Appendix C. 



105. The scour resulting from the interaction of the pier with waves 

 and currents produced a long, shallow trough under the pier (Figure 40). The 

 trough, generally 100 to 200 m wide and extending slightly past the seaward 

 end of the pier, changed depth, width, and symmetry in response to changing 

 wave conditions . 



106. Just inshore of the seaward end of the pier, the trough deepened 

 into a large scour hole (Figure 41). During storms such as that on 



13-16 November, this hole tended to deepen and expand in a downdrift direc- 

 tion (Figure 42). A more detailed description of the interaction of the pier 

 with waves and currents and the effect on the bottom can be found in Miller, 

 Birkemeier, and Dewall (1983). 



107. The largest changes in the bathymetry during 1981 occurred during 

 the November storm, when a large quantity of sediment moved from the north side 

 to the south side of the pier (Figure 43). In general, the response of the 



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