TM No. 377 



and 0.6 7 below the spectrum value to the 80$ confidence Limit spread* The 

 range of the upper and lower limits is shown in figure IV-8 as a vertical 

 bar indicated by R„ 



The frequency scale In figure IV-8 is in terms of miilicycles per kilo- 

 second (where 1 ksec - lb, 6? minutes),, which is abbreviated mcpks, 



The integral under the curve (the variance) is found to be 29 A9 cm 2 

 sec-2 s Most of the energy is associated with motions having frequencies 

 below 85 mcpks or periods greater than 13 ksec (3„6 hours),, Above 85 mcpks 

 peaks occur at 105 mcpks (a period of i60 min) at 170 mcpks (98 min), and 

 at 350 mcpks (k$ min). There is a minimum in the curve at about 310 mcpks 

 (a period of 79 min). The region from 310 to ^05 mcpks contains motions 

 depicted as the wiggles in the speed curve of figure JV-6. As an interesting 

 comparison., the auto-spectra of the free surface tide level £i*was computed 

 and is shown in figure IV-9. Both curves are similar in shape and show 

 peaking at the tide frequency* The speed function contains relatively mere 

 energy above the tidal frequency,, probably caused by The strong trend in 

 the general variation in the near, flow ever the nine-day sample . 



During the period 2U November (1200) through 8 December f0920) 1964. a 

 second series of current measurements was made from the BBELSc Series II 

 allowed a more the rough investigation of the. motions at 3BE1S than series 

 I. since it involved both longer sampling periods and shorter sampling 

 Intervals., The sane current meter system (Braincon histogram type) was 

 employed and suspended as before from the west end of the catwalk at 

 about 5 meters beneath the water surfaces 



For series II the histogram current meter was preset tc sample for 

 k minutes a Allowing I minute to advance the film, this gives a virtual 

 5 minute (0,3 ksec) sampling interval,, compared to 20 minutes (1,2 ksec) 

 for series I„ During the 1^-day sampling period., U00S data points of 

 current speed, current direction, instrument tilt angle, and tilt direction 

 were acquired., A supplementary record of tidal height yfij r *rs.s also obtained 

 from the C&GS tide gauge The data were processed at Braincon Corp. and in 

 the NUWS computer laboratory in a fashion similar to that discussed for 

 series I, 



Figure 17-10 shows a small segment of the record of tidal height y (cm),, 

 current speed § (cm sec-i), and current direction G (°7") — made from 2k 

 November (1230 hours) to 2? November (1000 hours). The ordinate scales are 

 identical to those in figure IV -6 for easy comparison. The time scale, how- 

 ever, is stretched to depict the greater density of points per unit time* 



Comparison of series II data with series T data indicates very similar 

 amplitude and phase relationships among the parameters y . <*r 1 and & * 

 These relationships were consistent throughout the long series II record,, 

 The 7 shows that maximum high water occurred about 1 hour- after the maximum 

 current £ and also at the time of northward current direction & , The 

 lesser peak of £ occurring at high tide plus k hours (2^-00 hours) is clearly 

 depicted on the series I record (figure XV-6)„ 



83 



