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TABLE No. 11

VELOCITY AND DISCHARGE IN SEWERS 4 TO 36 INCHES DIAMETER, OF VITRIFIED PIPE OR SMOOTH CONCRETE

Velocity in Feet per Second; Discharge in Cubic Feet per Minute; Sewers Flowing

Full

(Formula V =c√RS; c calculated by Kutter's formula, with n = .013. Q=60a V.)

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Q

.I 5.75 30.137.99 94.10 10.04 210.3 11.94 390.8 13.73 647.0 16.24 1196.0 18.59 1971.5

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TABLE No. 11-Continued

VELOCITY AND DISCHARGE IN SEWERS 4 TO 36 INCHES DIAMETER, OF VITRIFIED PIPE OR SMOOTH CONCRETE

Velocity in Feet per Second; Discharge in Cubic Feet per Minute; Sewers Flowing Full

(Formula V =cVRS; c calculated by Kutter's formula, with # =.013. Q = 60a V.)

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1076 7.24 1366 8.48 2497 9.06 3230 9.63 4085
962 6.47 1210 7.58 2233 8.11 2889 8.61 3653
833 5.60 1057 6.57 1934 7.02 2502 7.46 3164
679 4.56 860 5.35 1576 5.72 2040 6.08 2580
477 3.21
336 2.26

605 3.76 1109 4.02 1434 4.28 1814

427 2.66

782 2.84

1012 3.02 1281

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318 2.14

404 2.51

741 2.69

959 2.86 1213

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TABLE NO. 12

VELOCITY AND DISCHARGE IN SEWERS 33 INCHES TO 120 INCHES DIAMETER, OF BRICK OR CONCRETE OF ORDINARY SMOOTHNESS

Velocity in Feet per Second; Discharge in Cubic Feet per Minute; Sewers Flowing Full

(Formula V =c√RS; e calculated by Kutter's formula, with n =.015. Q=60a V.)

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TABLE NO. 12-Continued

VELOCITY AND DISCHARGE IN SEWERS 33 INCHES TO 120 INCHES DIAMETER, OF BRICK OR CONCRETE OF ORDINARY SMOOTHNESS Velocity in Feet per Second; Discharge in Cubic Feet per Minute; Sewers Flowing Full

(Formula V =c√RS; c calculated by Kutter's formula, with n =.015. Q=60@V.)

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8665 5.19 6110

8.32 14113 10.07 30370 11.63

54840

6000

100'

3.66

3.47

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.0007

.0006

2.82

.0005

.0004

.0003

.0002

2.24 3801
1.60 1882 1.82 3083 2.22 6694 2.58

5.87 9956 7.10 21435 8.21 4311 4.14 7030 5.02 15150 5.81 27380 4083 3.92 6659 3.27 3849 3.70 6276 3.05 3597 3.46 5870 4.20 3326 3.20 5429 3.88 2.57 3028 2.92 4946 2.29 2700 2.60 4411 1.97 2324

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1.37 1615 1.56
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1.39 2353 1.70 5137 1.99

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It is now generally considered that Kutter's formula gives somewhat too small values for sewers under 15 or 18 inches diameter.

Other formulas for calculating flow in sewers and similar conduits have been advocated from time to time. Perhaps of the recent ones that of Williams and Hazen has been most extensively used. This formula is as follows:

v=CRO 63 S0·54

Comparing this with the Chézy formula, it is seen that the c of that formula equals CR013 S0.04 in the Williams formula-a much simpler value than Kutter's c.

It must be remembered that the formulas and tables of velocity are supposed to apply only when the sewage has reached a constant velocity. Previous to this, when the friction does not consume all of h, the remainder is creating increments of velocity. Since the same amount of sewage must pass all sections of a sewer between two inlets, however, it follows that, previous to the flow obtaining its maximum and constant velocity, the depth of sewage must have been greater, increasing up stream to the point of entry. An initial velocity of entrance in the direction of the sewage flow will reduce the amount and extent of this non-uniform flow with larger crosssection, but will have little effect upon the ultimate constant velocity.

V is the mean velocity. The effect of friction is exerted along the wetted perimeter and grows less toward the center of the stream. The surface of flow also is retarded by friction with the air, and frequently in the case of house-sewage by a greasy scum which floats upon the surface. The velocity given is really the volume of flow divided by its area.

Since V varies as ƒ(R)=f(

area

er),

wetted perimeter,

it follows

that the size of the sewer and the shape of the cross-section have considerable effect upon the velocity of a stream. The

maximum value of

area

perimeter

for a sewer flowing full is obtained,

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