218 



areas of the cross section of the water prism while the flow is in the 

 opposite directions, and because of the distortions of the currents, tlie 

 total volume of flow in one direction may be expected to differ from 

 that in the other. This preponderance of flow may be estimated by 



computing the arithmetical mean 

 the given intervals. 



of the adjusted discharges at 



417. In the canal selected in 

 the first example the algebraic 

 mean of the finally computed 

 discharges at the initial en- 

 trance is —275 c. f. s. and at 

 the further entrance it is —158 

 c. f. s. A closer adjustment 

 would be necessary to remove 

 the discrepancy between these 

 two figures. The maximum 

 discharges at these entrances 

 are 22,220 c. f. s. and 50,700 

 c. f. s., respectively. These 

 figures show that in this case 

 the total volume of flow is 

 nearly the same in both direc- 

 tions, but indicate a slight 

 preponderance of flow toward 

 the initial entrance, where the 

 tidal range is the greater. 



418. In the Chesapeake and 

 Delaware sea-level barge canal, 

 taken as the second example, 

 the adjusted discharges pro- 

 duced by entrance tides on the 

 day selected show a prepon- 

 derance of flow averaging —441 

 c. f. s. at the initial entrance, 



station 5, and of —376 c. f. s. at the further entrance, station 77. 

 These figures indicate an average net discharge during the day of 

 about 400 c. f. s. through the canal in the negative direction, from 

 Chesapeake Bay into Delaware River. Tliis preponderance of flow 

 may be attributed to the higher mean tide elevation in the head of 

 Chesapeake Bay. 



419. It is not difficult to see that in a comparatively short canal, 

 with a wide difference in the tidal range at the two entrances, the tidal 

 elevations and the surface heads through the canal are dominated by 

 the tide at the entrance having the larger tidal range ; and because of 

 the greater cross section and less resistance to flow at the higher tidal 



Lunar Hour 



Primary Tides and Currents 

 Adjusted - 



FfGURE 73.— Primary and adjusted currents in first 

 example 



