210 



these depart from the simple harmonic fluctuations of the primary 

 entrance tides. The simplest adjustment, and one which appears as 

 tenable as any other, is to assign the departures of the total head 

 between the entrances to the primary heads in the subsections in 

 proportion to the length of the subsection. 



(b) The primary current in the subsection in which the amplitude, 

 B, is the greatest is corrected to conform to the adjusted tides at the 

 ends of the subsection, and for its other deformations, by the pro- 

 cedure described in chapter V. The currents in this subsection may 

 be expected to have the largest influence upon the currents through 

 the canal. 



(c) The discharges at the velocity station of this base subsection 

 are determined by multiplying the corrected velocity by the area of 

 the cross section at this station at the given time. 



(d) The currents at other stations are computed from those at 

 this base station by a cubature of the adjusted tides through a modi- 

 fication of the process developed in chapter VI. 



407. Example. — To illustrate the procedure, the corrected currents 

 in the Chesapeake and Delaware Canal will be computed from the 

 primary tides and currents derived in the preceding paragraphs, and 

 entrance tides conforming to the observed tides. To curtail the 

 computations, the small diurnal variation of the entrance tides is 

 omitted and the tidal cycle is completed in 12 lunar hours. The 

 representative tide at each entrance at zero hour (7 a. m., November 

 27, 1928) is taken as the mean of the recorded tides at and 12 lunar 

 hours; that at 0.5 lunar hour as the mean of the tides at 0.5 and 12.5 

 lunar hours; and so on. A minor adjustment at 11.5 hours produces 

 fairly smooth repeating tide curves with a period of 12 lunar hours. 

 The heights, above Delaware River datum, of the entrance tides so 

 derived are as follows: 



Selected entrance tides 



408. Adjustment of primary tides at ends of subsections. — The primary 

 heads in the subsections are given by the equation: 



hs=H cos (at^-H°) 



