What is considered a discoloration risk?
During normal operations, to know if there is discoloration risk you have to look at the results of the whole day and look for the maximum velocity:
- <0.3 m/s or <0.984252 ft/s max velocity cause sedimentation
- From 0.3 to 0.8 m/s or 0.984252 to 2.62467 ft/s max velocity pipes are “self-cleansing”, they don’t accumulate sediments.
And if you are performing flushing events:
- From 0.8 to 1.5 m/s or 2.62 to 4.92 ft/s could be a good flushing velocity, but in some cases not enough to remove biofilm
- >3 m/s or 9.84 ft/s is considered too much speed, which can cause issues in the network
- If there’s a big increase in velocity: from less than 0.2 (max velocity during the day) to 0.8 m/s or 0.66 to 2.62 ft/s) in any direction, it will allow for particle resuspension and could affect discoloration
The flow direction is reversed and the current velocity is >= 0.1m/s or 0.33 ft/s
|
Before flushing (max velocity during the whole day, Base Scenario) |
After flushing (max velocity during flushing, Flushing Scenario) |
State |
Reason |
0 to 0.3 |
0 to 0.3 |
Sedimentation |
Velocities too slow, particles fall to the bottom |
0 to 0.3 |
0.3 to 1.5 |
Discoloration risk |
Sediments that were deposited are lifted and transported |
0 to 0.3 |
1.5 to 3 |
Ideal velocities for flushing |
Capacity to flush away both the sediments and biofilm |
0.3 to 1.5 |
0 to 1.5 |
Nothing happens |
Pipe is self-cleansing on normal operation |
0.3 to 1.5 |
1.5 to 3 |
Ideal velocities for flushing |
Capacity to flush away both the sediments and biofilm |
1.5 to 3 |
1.5 to 3 |
Ideal velocities for flushing |
Capacity to flush away both the sediments and biofilm |
Greater than 3 |
Excessive velocities |
Possible problems in the network (water hammer) |