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PRELIMINARY 



1522 



(2) On cross-section paper, as illustrated in figure 4, plot the low- and high-water points A and E 

 in accordance with the time and height coordinates. 



(3) Divide the connecting line AE into four equal parts at points B, C, and D, 



(4) Take point B' vertically below B and point D' vertically above D, at a distance equal to 

 one-tenth of the range of tide. 



(5) Draw an approximate sine curve through points A, B' , C, D' , and E. This curve will closely 

 approximate the actual tide curve and the required data may be readily scaled from it. 



On the tide curve thus constructed the points at which changes in reducers occur 

 can then be marked (see 8224). Thus, when the reducers are desired in integral feet, 



Figure 4. — Construction of predicted tide curve. 



the curve should be marked at points 0.25 above each foot and the corresponding times 

 noted. A tabulation of reducers and times of change can then be taken from the 

 curve and furnished to each unit before starting each day's work. 



1522. Predicted Tide Curve 



When a predicted tide curve for a reference station is furnished by the Washington 

 Office, a time correction and range factor will usually be necessary to make the curve 

 applicable to the project area. These corrections will generally be indicated on the 

 curve by the Office. 



