6 



U. S. COAST AND GEODETIC SURVEY 



the tide and current curves in The Narrows, New York Harbor, for 

 August 8-9, 1922, the current curve being the dashed-Hne curve, rep- 

 resenting the velocities of the current in the center of the channel, 

 and the tide curve being the full-line curve, representing the rise and 

 fall of the tide at Fort Hamilton, on the eastern shore of The Narrows. 



The diagrams of figure 4 were drawn by plotting the heights of 

 the tide and the velocities of the current to the same time scale and 

 to such velocity and height scales as will make the maximum ordi- 

 nates of the two curves approximately equal. The time axis or axis of 

 X represents the line of zero velocity for the currents and of mean 

 sea level for the tide, the velocity of the current being plotted in 

 accordance with the scale of knots on the right, while the height of 

 the tide reckoned from mean sea level was plotted in accordance with 

 the scale in feet on the left. 



From figure 4 it is seen that the corresponding features of the 



Knots 



Figure 4.— Tide and current curves, The Narrows, New York Harbor, August 8-9, 1922. 



tide and current at this station bear a nearly constant time relation 

 to each other. This approximate constancy in time relations between 

 current and tide is characteristic of tidal waters in which the diurnal 

 inequality is small, and permits the times of slack and of strength of 

 the current to be referred to the times of high and low water. Thus, 

 from figure 4 we find that the strengths of the current come about 

 an hour before the times of high and low water, while the slacks come 

 about 1 % hours after high water and 3 hours after low water. In this 

 connection, however, it is to be noted that the time relations between 

 corresponding phases of tide and current at any place frequently 

 vary in consequence of disturbing effects of wind, weather, and fresh- 

 water run-off. 



Quite apart from the disturbing effects of nontidal agencies, the 

 time relations between current and tide are subject to variations in 

 regions where the tide exliibits considerable diurnal inequality; as 

 for example, on the Pacific coast of the United States. This variation 



