For all pipes, the Hydraulic Institute and many engineers consider the Colebrook equation most reliable for evaluating the friction factor.
Where
The Reynolds Number is defined as:
Where
The trick to solving the Colebrook equation is to select a friction factor that balances the left and right sides of the equation. Since the Reynolds number is dependent on viscosity, the temperature of runoff is of concern. The following table provides a range of viscosity of water at various temperatures.
|
Specific Gravity and Kinematic Viscosity of Water |
|
Temperature (deg F) |
Spec Gravity |
Kin. Viscosity (ft2/sec) |
|
40 |
1.000 |
1.664 |
|
50 |
1.000 |
1.410 |
|
60 |
0.999 |
1.217 |
|
70 |
0.998 |
1.059 |
|
80 |
0.997 |
0.930 |
|
90 |
0.995 |
0.826 |
|
100 |
0.993 |
0.739 |
|
110 |
0.991 |
0.667 |
|
120 |
0.990 |
0.610 |
|
150 |
0.980 |
0.475 |
StormShed3G™ currently assumes a default temperature of 68 deg F.