Which outcome is most directly associated with decreased velocity in sewer lines?

• A. Increased velocity
• B. Decreased velocity
• C. No effect
• D. Increased turbulence

Answer: (B)

When flow slows in a sewer line, there isn’t enough energy to keep solids in suspension. The reduced shear forces allow heavier particles to settle to the pipe bottom and accumulate as deposits. This deposition buildup is more likely because turbulence drops with lower velocity, so solids aren’t kept in motion. The practical result is a higher chance of blockages and reduced carrying capacity over time. In contrast, higher velocity would keep solids in suspension and increase mixing, while no change would imply velocity stays the same.