148 



-condition ordinarily will be met by stations spaced some miles apart, 

 but suitably placed with respect to marked changes in the cross section 

 of the channel. The stations used in the cubature of the Delaware 

 River by the United States Engineer Office at Philadelphia are as 

 follows: 



Distance from 



head of tide in 



Station statute miles 



1 . Trenton municipal pier 0. 45 



2. Trenton marine terminal 1.99 



3. Bordentown 5. 40 



4. Fieldsboro 6. 25 



5. Florence 11.08 



6. Burlington 15. 32 



7. Beverly 18.60 



8. Torres'dale 23.58 



9. Delair 29.11 



10. Philadelphia 33.20 



Distance from 



head of tide in 



Station statute miles 



11. Fort Mifflin 41.67 



12. Baldwins 48.45 



13. Marcus Hook 53.83 



14. Edge Moor 60.42 



15. Newcastle 67.52 



16. Reedy Point 75.15 



17. Reedy Island 78.88 



18. Artificial Island _,.- 83.62 



19. Woodland Beach 92.48 



20. Ship John 97.33 



It may be necessary to establish as well tidal stations on any long 

 tidal tributaries which enter the channel. For the convenience of the 

 computations the tide of all stations should be referred or reduced to 

 the same horizontal datum, preferably taken so low that all tidal 

 Tieights are positive. 



A reliable contour map is needed to show the tidal areas from low 

 ^water to liigh water and measurements must be made of the cross 

 sections of the channel at the stations where the velocities are to be 

 determined. 



302. A tidal channel whose cubature is to be made usually is the 

 tidal portion of a river with a considerable drainage area. In the 

 United States, gaging stations with established rating curves have 

 I)een established above the head of tide on most rivers, and the upland 

 •discharge of the main stream, and of any important tributaries which 

 «nter the tidal section can be ascertained therefrom. If satisfactory 

 rating curves have not been established, meter measurements should 

 be made, at suitable stations above the head of tide, of the upland 

 inflow frojm the .main stream and any important tributaries entering 

 the tidal section. The discharge from other drainage areas into the 

 tidal channel, including those below the gaging stations, is relatively 

 so small that it ordinarily can be derived with sufficient accuracy by 

 estimating, from general data, the run-off per square mile. 



303. Selection of representative tides for cubature. — The process of 

 ■cubature would become an overwhelming task if repeated through the 

 tides occurring during a considerable number of days. If the tides 

 are of the semidiurnal type, with no great variation in range during 

 the month, the cubature of the tides on a single day, chosen almost 

 at random, will develop the characteristic fluctuations in the discharge 

 and in the velocity at stations along the channel. The effect of the 



