What is the minimum design velocity for a sewer meant to be greater than?

The minimum design velocity for a sewer system is typically established to ensure effective self-cleansing of the pipes. A design velocity of 2 feet per second is considered a standard minimum because it is sufficient to prevent the deposition of solids, which can lead to blockages and maintain the flow stability in the sewer system.

When the flow velocity is above this threshold, it helps to ensure that waste and debris are effectively carried away, reducing the risk of clogs and backups. This velocity is a balance between being fast enough to keep solids in suspension while also being low enough to minimize excessive wear and noise in the system.

Velocities lower than 2 feet per second may not provide adequate self-cleaning, while velocities significantly higher can increase the wear on the pipeline and lead to additional costs related to the infrastructure maintenance. Hence, a design velocity of at least 2 feet per second is established as a best practice in sewer design.