







7 











10 Consecutive Surveys 





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and Standard Deviation - 



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40 60 80 

 Distance Offshore, m 



Figure 2-6. Repetitive profile surveys and standard deviation of profile elevation 



on the order of the depth of footprints on the dry sand. All lines on 

 Figure 2-6 are coincident, with die exception of one line in the range of 62 to 

 66 m. This one obvious error was caused by wheel floating, which would 

 tend to occur in deeper water where the hollow survey rod was mostly 

 submerged and buoyant. Routine data inspection of the profile data at the end 

 of the survey, as described above, revealed most of these errors, and the data 

 were edited or the profile re-surveyed. In the present case, the obvious wheel 

 float was allowed to remain as an example. 



Because measurements in the repetitive survey were not made at exactly 

 the same location along the channel, the data were interpolated to obtain uni- 

 form spacing, and the standard deviation in elevation in Figure 2-6 was com- 

 puted at each point. The standard deviation was less than 0.3 cm over most 

 of the profile. The deviation was greater, however, in the nearshore region 

 where the proximity of the Geodimeter to the prism tended to introduce error. 

 It was difficult to overcome this near-field error because the location of the 

 Geodimeter was limited by the wall of the enclosure. The standard deviation 

 was also relatively high on the shoreward side of the bar, where repeated 

 impact of the tires may have disturbed the bed, and on the offshore side of the 

 bar. On the offshore side of the bar, large ripples that were observed to form 



Chapter 2 Beach Profile Surveys and Sediment Sampling 



49 



