3 

 1.019 g/cra occur less than 7 percent of the time. Values less than 



3 

 1.016 g/cm , which occurred only during the summer of 1984, account for only 



1.7 percent of all measurements to date. 



Surveys 



101. 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, 



102. To document the temporal and spatial variability in bathymetry, 

 surveys were conducted approximately monthly of an area extending 600 m north 

 and south of the pier and approximately 950 m offshore. In addition, monthly 

 soundings were taken along both sides of the pier. 



103. A brief discussion of the effect of the research pier on the sur- 

 rounding bathjonetry precedes discussions of time-histories of bottom eleva- 

 tions at selected locations along the pier and contour diagrams of the 

 bathymetry. 



Pier effect 



104. The research pier introduces a perturbation in bathymetry (Fig- 

 ure 43) in the form of a permanent trough under the pier, apparently a result 

 of the interaction of waves and currents with the pilings. The trough deepens 

 under the seaward end of the pier and varies in shape and depth with changing 

 wave and current conditions. The pier's effect 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). 



History of bottom elevation 



105. A history of the bottom elevations is presented at the Baylor wave 

 gage locations, pier sta 6+20 (189 m) and 19+00 (579 m) (Figure 44). This 

 information is useful for interpretation of the wave data from gages 625 



and 615 located under the pier. Histories at intermediate locations at 323 

 and 433 m are also included (Figure 44) . Variations of elevation under the 

 pier are caused by natural processes (such as profile changes caused by bar 

 movement) as well as scour caused by the interaction of the pier piles with 

 waves and currents. Throughout the year the depth of the scour hole at the 

 seaward end of the pier varied approximately 0.6 m. This is relatively low in 



69 



