III. TIDE OBSERVATIONS 
Location of Tide Station 
In selecting the site for a tide station, a number of factors must be taken into 
consideration. Of these the more important are free communication for the tide, 
sufficient depth of water even at extreme low tide, shelter from storm waves, com- 
parative freedom from freshets, and accessibility in all kinds of weather. 
In passing over areas of shoal water, the tide is affected profoundly, both in time 
and in height; hence sites near the heads of tidal bays and rivers are not suitable for a 
tide station that is to be representative for any considerable area. In tidal rivers 
draining large areas, the effects of freshets or of seasonal variation in volume of drainage 
waters are most pronounced in the upper reaches, but become less pronounced farther 
seaward. 
As will be seen later, the range of tide is sensitive to changes in the hydrographic 
features of a body of water. Hence small bays or bights connecting with the sea through 
narrow and shallow openings subject to change are, in general, not suitable for tide 
stations intended for furnishing fixed tidal datum planes. 
Tide Staff 
The simplest means for obtaining tidal observations consists in the use of a tide 
staff. This may be made from a board 5 to 6 inches wide and 1 inch thick, graduated 
to feet and tenths, with the numbers increasing upward. It should be of such length 
that the extreme fluctuation of the water in the locality in which it is to be used will be 
within its lowest and highest graduation, and it should be fastened securely in a vertical 
position to a pile or other suitable support. 
Where the surface of the water is disturbed by considerable wave motion, it becomes 
difficult to read the height of the tide with any degree of accuracy. In such cases it is 
of advantage to fasten a glass tube to the face of the staff. Stock glass tubing about 
one-half inch in diameter, having a wall thickness of about one thirty-second of an 
inch and about 6 feet in length, has been found quite satisfactory. The tubing may be 
secured to the face of the staff by means of spring clips or cup hooks. The wave motion 
is reduced by partially closing the submerged end of the tube by a notched cork. A 
floating object introduced into the tube, such as a thin slice of cork having a diameter 
somewhat less than that of the tube, then permits the reading of the height of the water 
with ease to the nearest tenth or half tenth of a foot. 
Where the tide staff is to be used for a considerable period of time, and therefore 
subject to weathering, it will be found of advantage to cut the graduations denoting the 
feet and tenths into the wood and to form the figures marking each foot from brass 
upholstery tacks. 
To obviate the difficulties resulting from the defacement of the graduations on a 
_ wooden tide staff, which in polluted waters may become illegible in a comparatively 
23 
