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```									CPM Concrete Drainage Systems

Pipeline design - hydraulic

Graph showing relative velocity and discharge in a circular pipe for any depth of flow

1.0

0.9

0.8

0.7
Proportional depth of flow

0.6
E
A   RG
0.5                                                     CH
IS
LD
NA
TIO
0.4
P   OR
P   RO

0.3

C    ITY
0.2                                                               LO
VE
AL
T   ION
OR
0.1                                    OP
PR

0
0   0.1   0.2         0.3          0.4            0.5             0.6     0.7   0.8   0.9   1.0   1.1   1.2

Proportional velocity and discharge in pipes flowing part full

For calculating transitional flow, using the Colebrook-White equation, a roughness factor of Ks = 0.3mm
is recommended as a realistic figure for newly installed concrete pipelines. However, research has
indicated that for mature foul sewers of any material the Ks value may rise well above this figure and the
Water Services Association publication Sewers for Adoption 5th Edition recommend the following:

Foul and combined sewers Ks = 1.5mm (minimum velocity should be 0.75m/ see at one third design
flow)
Surface water sewers Ks = 0.6mm (minimum velocity should be 1m/sec at full pipe flow)

Hydraulic flow charts have therefore been included for the three roughness coefficients Ks of 0.3, 0.6
and 1.5mm.
CPM Concrete Drainage Systems

Pipeline design - hydraulic

Example on use of flow charts

Design of surface water sewer

Pipeline length                                   200m
Difference in level between inlet and outlet      1m
Design discharge                                  4 cubic metres/sec
(4,000 litres/sec)

to determine the size of pipe when:
a. flowing full
b. the proportional depth of flow is 0.6 (i.e. 60% full)

Solution

Hydraulic gradient                    1 in 200 (or 0.005)
Ks for surface water sewer            0.6mm

a. Pipe flowing full:
Refer to Hydraulic Flow Chart for Ks = 0.6mm.
The intersection of the horizontal discharge line of 4 cubic metres per second with the vertical hydraulic gradient
line of 1 in 200 gives:

Pipe diameter                         1350mm
Average velocity                      2.8 metres/sec

b. Pipe flowing 60% full:
Refer to the graph showing Relative.
Velocity and Discharge in a Circular pipe for any Depth of Flow.

The intersection of the horizontal proportional depth line of 0.6 with the proportional discharge and velocity curves
gives:

Proportional discharge                0.67
Proportional velocity                 1.07

Therefore

Actual discharge         0.67 x 4                 2.68 cubic metres/sec
Average velocity         1.07 x 2.8               3.0 metres/sec
CPM Concrete Drainage Systems

Pipeline design - hydraulic

Hydraulic flow charts

For Pipes Flowing Full Ks = 0.3mm (Colebrook-White) Water 150C
CPM Concrete Drainage Systems

Pipeline design - hydraulic

Hydraulic flow charts

For Pipes Flowing Full Ks = 0.6mm (Colebrook-White) Water at 15°C
CPM Concrete Drainage Systems

Pipeline design - hydraulic

Hydraulic flow charts

For Pipes Flowing Full Ks = 1.5mm (Colebrook-White) Water at 15°C

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