Scattergraph Principles and Practice
Powerful Tools Representing Depth and Velocity Sewer Flow Data
The Scattergraph is a powerful tool that displays depth and velocity data from a sewer flow monitor. The resulting patterns form characteristic signatures that provide insight into the conditions within a sewer. The flow monitor data also leave distinct patterns that even allow the performance of the flow monitor itself to be evaluated.
Surcharge conditions are common in sewer systems, especially during wet weather events. The flow monitoring data shown in the Scattergraph at the left indicate that this sewer operates as expected up to its rated capacity of 20.8 MGD. This value is shown using an iso-Q. Although surcharge conditions are common, it is uncommon to find a surcharged sewer that actually accommodates its rated capacity, as shown in this example.
The minimum and maximum dry weather flow rates are also shown using iso-Qs. The maximum dry weather flow rate occurs at a depth-to-diameter (d/D) ratio or 0.77, a depth in excess of generally accepted design guidelines.