no 



HYDROGRAPHIC MANUAL 



gage is designed for use at primary stations, 

 or at stations where observations are to be 

 continued for long periods of time (see 2- 

 50). The portable gage requires a less elabo- 

 rate installation and is used at tide stations 

 where a comparatively short series of obser- 

 vations are required. Both types of gages 

 are activated by a float as it rises or falls 

 in a well. 



Float wells may be constructed of various 

 materials to suit the conditions of installa- 

 tion. The float used with a standard tide 

 gage is 81/2 inches in diameter, and the port- 

 able tide gage float is 314 inches in diameter. 

 Rough lumber may be used to construct the 

 wells at any temporary station. The heavy 

 iron or steel pipes which have been used for 

 many years are being replaced by lighter 

 material such as molded fiber glass, polyvinyl 

 chloride pipe, and various types of soil pipe. 

 The fiber glass is particularly suitable for 

 use at permanent installations. 



A new type of pressure gage is being 

 tested, and is called a "bubbler" gage. One 

 end of a small tube is held at a fixed position 

 below the surface of the water and air or gas 

 under pressure is fed into the tube so that 

 small amounts will escape through the sub- 

 merged end at the highest tide expected. The 

 other end of the tube is connected to a pres- 

 sure measuring element which is self-com- 

 pensating for atmospheric pressure and tem- 

 perature. The change in pressure caused by 

 the tide is measured and recorded graphic- 

 ally. A telemetering device can be used at 

 the gage to transmit the information by ra- 

 dio or telephone to a distant recorder. 



Complete instructions for installation and 

 servicing of all types of gages, except the 

 pressure gage, are contained in Special Pub- 

 lication No. 196. All installations shall com- 

 ply with these instructions. 



3-143 Tide 



tion, Form 681, 

 cate for each 

 inspected. The 

 by spirit levels 

 marks and the 

 corded in Form 

 Station. These 



records. — Report — Tide Sta- 

 shall be submitted in dupli- 



tide station established or 



tide staff shall be connected 

 with at least three bench 

 results of the leveling re- 

 258, Leveling Record — Tide 



reports and records shall be 



forwarded to the Ofiice promptly (see 2-52). 

 The exact location of each tide station 

 shall be shown on hydrographic sheets. The 

 time meridian used shall be shown on tide 

 records. The marigrams from portable gages 

 shall be forwarded to Washington for each 

 two weeks of satisfactory operation, if prac- 

 ticable. When a station is discontinued, it 

 shall be noted on the original tide record. 

 The roll on a standard tide gage shall be 

 removed and forwarded to the Office on the 

 first day of each calendar month or as soon 

 thereafter as possible. Hourly heights re- 

 quired for reduction of soundings shall be 

 scaled from portable gage records by the 

 field party before the marigrams are for- 

 warded to Washington. Hourly heights from 

 standard gage records will be furnished by 

 the Washington Office on request. 



3-144 Current meters. — Current veloci- 

 ties are measured by three instruments: 

 current pole and log line. Price current meter, 

 and Roberts Radio Current Meter. The first 

 two are described in Special Publication No. 

 215, Manual of Current Observations, and 

 the third in the Roberts Radio Current 

 Meter Operating Manual, 1952 Edition. 



The current pole and Price meter obser- 

 vations are made from a vessel at anchor. 

 The meter may be suspended at any desired 

 depth, but provides information as to velocity 

 only. The radio meter is suspended from a 

 specially designed buoy which contains the 

 radio transmitter and on which an antenna 

 is mounted. One, two, or three meters 

 may be suspended from the same buoy 

 and data transmitted from each meter 

 in turn at intervals determined by op- 

 eration of a sequence switch. The meter 

 measures the velocity and direction of the 

 current. The data are recorded on chrono- 

 graph tapes through a radio receiver aboard 

 the survey vessel. A recorder may be in- 

 stalled in the buoy and the data recorded 

 automatically on waxed tape. Special in- 

 structions are issued with the recorder. 



In the past, each buoy transmitter was 

 assigned a frequency and broadcast data 

 continuously. With this system, it is neces- 

 sary to tune in each buoy individually to 



