Module 2 ยท Follow the Flow
Manholes
Manholes provide access and show what the sewer is doing at key points.
A manhole has a cover and frame at the surface. Below them are the cone and the vertical barrel. The invert is the shaped channel at the bottom that carries wastewater through the structure. The bench is the raised area beside that channel.
Operators may inspect flow from the surface or lower cameras and cleaning tools. For example, a high water mark on the wall may show that the sewer backed up earlier.
An open manhole creates fall, traffic, and confined-space hazards. Trained staff guard the opening and test the atmosphere. A manhole is never safe simply because it looks empty from above.
Exam Need to Know
- Invert: the formed flow channel in a manhole's floor.
- Bench: the raised shelf next to the invert.
- A waterline stain on manhole walls shows an earlier backup.
Exam area: Sewer System Features