Which type of sewer would be used to relieve an overloaded main sewer?

• A. Relief sewer
• B. Outfall sewer
• C. Storm overflow sewer
• D. Depressed sewer

Answer: (A)

Relief sewer is used to relieve an overloaded main sewer by providing an alternate path for excess flow, which helps prevent surcharges and backups in the trunk. It’s installed in parallel or tapped into the main at strategic points so that during peak capacity or when the main sewer is nearing capacity, part of the flow can be diverted into the relief line and carried to a downstream point with available capacity. This keeps the overall system functioning by balancing flow and reducing the chance of overflows.

An outfall sewer is the line that carries sewage to a treatment facility or discharge point, not specifically to relieve an overloaded trunk. A storm overflow sewer handles excess stormwater or combined sewer overflow during heavy rainfall, not the routine relief of sanitary sewer capacity. A depressed sewer is simply a sewer laid at a lower grade to pass under obstacles or other utilities, not a purpose-built relief path for an overloaded main.