tertiary tide station— A tide station at which continuous observations have been made over a 

 minimum period of 30 days but less than 1 year. The series is reduced by comparison 

 with simultaneous observations from a secondary control tide station. This station 

 provides for a 29-day harmonic analysis. See tide station, primary control tide station, 

 subordinate tide station (1), and secondary control tide station. 



tidal bench mark— See bench mark. 



tidal bench-mark description— A pubUshed, concise description of tlie location, stamped 

 number or designation, date estabUshed, and elevation (referred to a tidal datum) of a 

 specific bench mark. 



tidal bench-mark State index map— A State map which indicates tlie locations for which 

 tidal datums and tidal bench-mark descriptions are available. 



tidal bore— A tidal wave that propagates up a relatively shallow and sloping estuary or river 

 in a solitary waveform. The leading edge presents an abrupt rise in level, frequently with 

 continuous breaking and often immediately followed by several large undulations. An 

 uncommon phenomenon, the tidal bore is usually associated with verj' large ranges in 

 tide as well as wedge-shaped and rapidly shoaling entrances. Also called eagre, eager (for 

 Tsientang, China, bore), mascaret (French), pororoca (Brazilian), and bore. 



tidal constants— Tidal relations that remain practically constant for any particular locahty. 

 Tidal constants are classified as harmonic and nonharmonic. The harmonic constants 

 consist of the amplitudes and epochs of tlie harmonic constituents; tlie nonharmonic 

 constants include the ranges and intervals derived directly from the high and low water 

 observations. 



tidal datum— See datum. 



tidal day— Same as lunar day. 



tidal difference— Difference in time or height of a high or low water as a subordinate station 

 and at a reference station for which predictions are given in tide tables. The difference, 

 positive or negative when appUed to the prediction at the reference station, gives the 

 corresponding time or height for the subordinate station. 



tide— The periodic rise and fall of the water resulting from gravitational interactions between 

 tlie Sun, Moon, and Earth. The vertical component of the particulate motion of a tide 

 wave. Altliough the accompanying horizontal movement of tlie water is part of the same 

 phenomenon, it is preferable to designate this motion as tidal current. 



tide curve— A graphic representation of the rise and fall of the tide in which time is usually 

 represented by the abscissa and height by the ordinate of the graph. For a normal tide 

 the graphic representation approximates a cosine curve. 



