Scattergraph Principles and Practice: Tools and Techniques to Evaluate Sewer Capacity

The scattergraph is a graphical tool used to evaluate flow monitoring data from sewer systems. The scattergraph depicts a relationship between flow depth and velocity and provides insight into the hydraulic conditions within a sewer. The addition of iso-Q™ lines brings a new dimension – flow rate – to the scattergraph and illustrates the impact that existing hydraulic conditions have on the operational capacity of a sewer. Simply put, an iso-Q is a line of constant quantity and is analogous to a contour line on a topographic map. The concept of the iso-Q is presented and developed in this paper. Practical examples from flow monitoring locations throughout the United States are also provided, demonstrating the use of iso-Qs to evaluate the operational capacity of existing sewers under a variety of conditions.