PART V: TIDES AND WATER LEVELS 



Measurement Instrument 



64. 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, Oreg.) 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. 



65. The tide gage was checked daily for proper operation of the punch 

 mechanism and for accuracy of the time and water level information. The accu- 

 racy was determined by comparing the gage level reading with a level read from 

 a reference electric 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 se- 

 vere, divers inspected and cleaned the orifice opening as required. 



66. 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. NOS and FRF personnel 

 also reviewed procedures for tending the gage and handling the data. Any spe- 

 cific comments on the previous months of data were discussed to ensure data 

 accuracy. 



67. 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 val- 

 ues was created for visual inspection. If errors were encountered, a computer 

 program was used to fill in or recreate bad or missing data using correct val- 

 ues form 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 tab- 

 ulations of daily highs and lows, hourly heights (instantaneous height se- 

 lected on the hour) , and various extreme and/or mean water level statistics 



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