The relationship between flow depth and velocity is important to understanding the hydraulic conditions in a sewer. The addition of flow rates to a scattergraph deepens the operational understanding of these conditions. Flow rates can be scaled within a scattergraph and displayed using iso-Q lines.
Simply put, an iso-Q is a line of constant quantity and is analogous to a contour line on a topographic map. Iso-Qs play an important role in evaluating sewer capacity and are incorporated in the following panels as either actual flow rates or a percent of full-pipe capacity.