215 



gives the velocities at station 51+200, in column (12). The compu- 

 tation for the rest of the 12-hoiir cycle is in the same form. 



413. The velocities at the entrance to the canal at Chesapeake City 

 Bridge, station 77, are similarly derived by cubatiire from station 69. 

 The discharges at station 37 are derived from those at 51+200, and 

 thence successively the discharges and velocities at station 19 + 500 

 (Biddies Point) and at station 5 (Reedy Point). The flow through 

 the branch canal which makes off from near Biddies Point is too small 

 to warrant the labor involved in including it in the adjustment. The 

 surface areas, U, and the areas of the cross sections, used for these 

 computations, are as follows: 



Surface areas, U {square feet) 



Reach tide 6.0 foot tide 



Stations 69 to 77— prism 1 , 406, 000 1 , 646, 000 



Back Creek 583,000 4,294,000 



Total 1,989,000 5,940,000 



Stations: 



51 + 200 to 69 3,128,000 3,662,000 



37 to 51 + 200 3,505,000 7,699,000 



19+500 to 37 4,294,000 9,447,000 



5 to 19 + 500 8,208,000 13,568,000 



Cross sections, X {square feet) 



Stations : O tide 6.0-foot tide 



From 45 to 77 1,900 2,944 



19 + 500 1,936 3,065 



5 2,428 4,060 



414. Comparison with observed velocities. — ^The computed primary 

 currents and adjusted currents, at Reedy Point (station 5) and at 

 Biddies Point (station 19 + 500) and the mean velocities from meter 

 measurements at these stations on November 27-28, 1928, are shown 

 in figure 71, page 216. It may be seen that the adjustments produce 

 large distortions of the primary velocity curves at these stations. 

 While the recorded velocities are somewhat erratic, the adjusted 

 velocities conform fairly well to the observations. The computed 

 and observed currents at Summit Bridge (station 51 + 200) and at 

 Chesapeake City Bridge (station 77) are shown in figure 72, page 217. 

 The recorded velocities at these stations are much more consistent, 

 and with some minor variations the adjusted currents resulting from 

 the computations are in close accordance therewith. Although the 

 constants and data used in the computations were selected without 

 regard to the observed currents, the agreement is perhaps closer than 

 could ordinarily be expected. 



