PART V: TIDES AND WATER LEVELS 



Measurement Instrument 



47. Water level data were obtained from a NOAA/NOS control tide station 

 (sta 865-1370) located at the seaward end of the research pier (Figure 2) by 

 using a Leupold and Stevens, Inc. (Beaverton, OR) digital tide gage. This 

 analog-to-digital recorder is a float-activated, negator-spring, counterpoised 

 instrument that mechanically converts the vertical motion of a float into a 

 coded, punched paper tape record. The below-deck installation at pier 



sta 19+60 consisted of a 30.5-cm-diam stilling well with a 2.5-cm orifice and 

 a 21.6-cm-diam float. 



48. Operation and tending of the tide gage conformed to NOS standards. 

 The gage was checked daily for proper operation of the punch mechanism and for 

 accuracy of the time and water level information. The accuracy was determined 

 by comparing the gage level reading with a level read from a reference elec- 

 tric tape gage. Once a week, a heavy metal rod was lowered down the stilling 

 well and through the orifice to ensure free flow of water into the well. 

 During the summer months, when biological growth was most severe, divers 

 inspected and cleaned the orifice opening as required. 



49. The tide station was inspected quarterly by a NOAA/NOS tide field 

 group. Tide gage elevation was checked using existing NOS control positions, 

 and the equipment was checked and adjusted as needed. Both NOS and FRF 

 personnel also reviewed procedures for tending the gage and handling the data. 

 Any specific comments on the previous months of data were discussed to ensure 

 data accuracy. 



50. Digital paper tape records of tide heights taken every 6 min were 

 analyzed by the Tides Analysis Branch of NOS. An interpreter created a digi- 

 tal magnetic computer tape from the punch paper tape, which was then processed 

 on a large computer. First, a listing of the instantaneous tidal height 

 values was created for visual inspection. If errors were encountered, a com- 

 puter program was used to fill in or recreate bad or missing data using cor- 

 rect values from the nearest NOS tide station and accounting for known time 

 lags and elevation anomalies. The data were plotted, and a new listing was 

 generated and rechecked. When the validity of the data had been confirmed, 

 monthly tabulations of daily highs and lows, hourly heights (instantaneous 



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