Proposed surrogate hydraulic variables for the assessment of the potential for discolouration incidents
| Components of discolouration management . | Surrogate hydraulic variable . | Threshold . |
|---|---|---|
| Nodal water age (demand and non-demand nodes) | – | No absolute threshold exists. Distribution of nodal water age should be characterised |
| Pipe residence time (metal pipes) | Diurnal flow velocity range | Flow velocity should be above 0.06 m/s |
| Self-cleaning condition (sedimentation) | Maximum diurnal flow velocity | ≥0.2 m/s |
| Self-cleaning condition (strongly adhered materials) (plastic and AC pipes) | Maximum diurnal shear stress | ≥1.2 N/m2 |
| Cleaning (strongly adhered materials) (metal pipes) | Maximum diurnal flow velocity | No established threshold exists. A higher velocity reduces the risk of discolouration |
| Biofilm cleaning | Ratio of maximum diurnal velocity to average diurnal velocity (or shear stress) | 1.5 (2.3), the higher ratio is more likely to facilitate the cleaning process |
| Ratio of maximum diurnal velocity to minimum diurnal velocity (or shear stress) | 1.5 (2.3), the higher ratio is more likely to facilitate the cleaning process | |
| Maximum diurnal shear stress | ≥2 N/m2 (when growth occurs between 0.01 and 0.3 N/m2) | |
| Flow direction | No established absolute thresholds exists for the magnitude and duration of flow reversal (and velocity) |
| Components of discolouration management . | Surrogate hydraulic variable . | Threshold . |
|---|---|---|
| Nodal water age (demand and non-demand nodes) | – | No absolute threshold exists. Distribution of nodal water age should be characterised |
| Pipe residence time (metal pipes) | Diurnal flow velocity range | Flow velocity should be above 0.06 m/s |
| Self-cleaning condition (sedimentation) | Maximum diurnal flow velocity | ≥0.2 m/s |
| Self-cleaning condition (strongly adhered materials) (plastic and AC pipes) | Maximum diurnal shear stress | ≥1.2 N/m2 |
| Cleaning (strongly adhered materials) (metal pipes) | Maximum diurnal flow velocity | No established threshold exists. A higher velocity reduces the risk of discolouration |
| Biofilm cleaning | Ratio of maximum diurnal velocity to average diurnal velocity (or shear stress) | 1.5 (2.3), the higher ratio is more likely to facilitate the cleaning process |
| Ratio of maximum diurnal velocity to minimum diurnal velocity (or shear stress) | 1.5 (2.3), the higher ratio is more likely to facilitate the cleaning process | |
| Maximum diurnal shear stress | ≥2 N/m2 (when growth occurs between 0.01 and 0.3 N/m2) | |
| Flow direction | No established absolute thresholds exists for the magnitude and duration of flow reversal (and velocity) |