a. Staff Wave Gages . Three staff gages are used to collect wave data as 

 part of the BEM. Two gages are located at stations 6+20 and 19+00; the third 

 gage is located at Jennette's fishing pier (about 25 miles south of the FRF), 

 Nags Head, North Carolina. 



The wave staffs are parallel inductive cable types manufactured by the 

 Baylor Company, Houston, Texas (Fig. 3). Each wave staff consists of two wire 

 ropes 0.5 inch in diameter held parallel under tension 9 inches apart. Asso- 

 ciated with each staff is a transducer element which yields an electrically 

 linear (direct current) output that is proportional to the amount of cable 

 above a short circuit on the staff caused by the conducting characteristics of 

 seawater. The gage is designed for an accuracy and resolution of 1 and 0.1 

 percent full scale, respectively. (For additional details on the wave staffs, 

 refer to Baylor Company, 1970.) The gage installations at stations 6+20 and 

 19+00 use a hanger bracket support at the top and an anchor system on the bottom 

 which are centered under the pier deck midway between adjacent pilings (Fig. 3). 

 The Nags Head staff has rigid top and bottom supports connected directly to a 

 wooden piling on the north side of the pier . 



The water depth at each gage fluctuates as a function of both the water 

 level and bottom elevation. Figure 4 shows the maximum and minimum bottom ele- 

 vations observed along the FRF pier between 27 July 1977 and 4 January 1979. 



b . Wave Measuring Buoys . Two Datawell Waverider buoy wave sensors are de- 

 ployed at the FRF (Fig. 5). One sensor is located near the seaward end of the 

 pier in about 23 feet of water; the other sensor is 1.3 miles due east of the 

 end of the pier in about 60 feet of water (Fig. 2). The Waverider is a buoy 

 which follows the movement of the water surface with internal electronics that 

 measure the vertical acceleration of the buoy. The signal is integrated twice 

 to produce a surface displacement signal which is telemetered to a shore re- 

 ceiving station. 



The mooring used to fix the buoy in position is an integral part of the wave 

 measuring system, designed to allow the buoy to move freely with the sea surface 

 but strong enough to withstand the large forces caused by storm waves. Figure 

 6 shows the near shore and offshore Waverider mooring systems at the FRF. The 

 mooring components and their dimensions are a function of the water depth where 

 the buoys are deployed. The offshore mooring system (deployed in about 60 feet 

 of water) consists of a black rubber stretch cord, a buoyant polypropylene white 

 rope, and a nylon-covered, stainless-steel rope covered with an air compressor 

 hose cut into 8-inch lengths (foreground of photo in Fig. 6). The air compressor 

 hose protects the rope from abrasion as it is dragged back and forth on the ocean 

 bottom. The nearshore mooring system consists only of the rubber cord for de- 

 ployment in depths of 25 feet or less (background of photo in Fig. 6). Addi- 

 tional details on the buoy operation and mooring configuration are in Van Breugel, 

 Verhagen, and Gerritzen (1972) . 



c. Pressure Wave Gage . A single pressure gage is installed under the sea- 

 ward end of the FRF pier. The gage sensor consists of a transducer (manufactured 

 by I.C. Transducers, Inc., San Jose, California), coupled to a Bellofram gage 

 protector and enclosed in a PVC housing (Fig. 7). With this arrangement, the 

 pressure is sensed by the diaphragm in the gage protector and transmitted by an 

 oil-filled cavity to the transducer. (Additional details on the transducer may 

 be obtained from the manufacturer.) The gage is located at station 19+40 in 

 approximately 27 feet of water (Fig. 2). The pressure sensor is attached to 



a special T-shaped bracket anchored to the bottom (Fig. 8). 



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