09. Surcharge

Surcharge conditions are common in sewer systems, especially during wet weather event.  The flow monitoring data shown here 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 here.

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.