214 



412. The ciibature between stations 69 and Summit Bridge, station 

 51+200, takes the following form: 



Cubature — stations 69 to 51+200 



The tides at station 69, column (2), are those shown in column (5) of 

 the preceding tabulation. Those at station 51 + 200, column (3), are 

 derived by linear interpolation between the adjusted tides at stations 

 45 and 61. The mean tide in the reach fro.m station 51+200 to 

 station 69 is shown in column (4). The increase in the mean tide in 

 the preceding interval is entered in column (5), the entry at hour 

 being repeated from that for 12 hours (not shown). The mean of the 

 entries on the half hour and on the succeeding half hour, in column (5), 

 gives the mean rise during the preceding and following intervals, and 

 is the value of Ay, column (6). The area, U, of the water surface 

 between stations 69 and 51+200, from topographical maps of the 

 canal, is 3,128,000 square feet at zero tide, and 3,662,000 square feet 

 at a 6.0 foot tide. Dividing by A#=1863, the value of U/At at tide 

 is 1,679, and at 6-foot tide, 1,966. The values of U/At at the mean 

 tidal heights shown in column (4) are taken off a straight line diagram 

 and entered in column (7). The values of AQ, column (8), are then 

 the products of the entries in columns (6) and (7), with the sign 

 reversed. The discharges at station 69, previously found, are entered 

 in column (9). Since the cubature is in the negative direction, the 

 values of AQ are subtracted therefrom, algebraically, to give the 

 discharges at station 51 + 200, column (10). The typical cross sections 

 of the canal show the same section at station 51+200 as at station 69, 

 and the areas X of the cross section at the latter station, at the tidal 

 heights shown in column (3) are taken from the diagram previously 

 prepared. The quotient of the entries in columns (10) and (11) then 



