206 



396. Mean sea level oj primary tides. — The mean sea level at the two 

 entrances as found in the precedmg paragraph differs by 0.31 feet. 

 Long period observations show a similar difference. For the com- 

 putation of the primary currents and tides the elevation of mean sea 

 level is taken as the mean of the elevations at the entrances, or 2.63 

 feet above Delaware River datum. The depth of the bottom of the 

 canal is then 14.63 feet throughout. 



397. Division into subsections. — A subdivision based on the variation 

 in the cross section and in the storage areas is shown in figure 68; 

 station 5+000 being selected as the initial entrance. 



5 



BaeK.Cr 



Figure 68.— Diagram of Chesapeake and Delaware Canal. 



The subsections and their constants are: 



The velocity stations, column (3), are the midpoints of the subsec- 

 tions. Station 37, nearest the middle of canal, is taken as the base 

 station for velocities. The cross section areas, M, column (4), and 

 the surface widths of the canal, z, column (6), are at mean tide, 2.63 

 feet above datum, and are taken from a sheet of measured cross sec- 

 tions. Since the area at the base station is 2400, the values of m, 

 column (5), are 2400/M. The hydraulic radius, r, column (7), is taken 

 as M/2, and the Chezy coefficients C, column (8) , are from the Bazin 

 formula, 0=87/(0. 552 + "m'VVr), with "m" = 1.30. The "m" in this 

 formula has no relation to the ratio m in the tabulation. The cor- 

 responding values of p (equation 286) and of la/g (par. 373) are shown 

 in columns (9) and (10). 



398. The surface areas, U, at mean tide, between the velocity sta- 

 tions, and between the entrances and the adjacent velocity stations. 



