What is the purpose of the minimum scouring velocity value in sanitary mains?

• A. To set maximum flow velocity
• B. To determine pipe diameter for new mains
• C. To ensure sediments are scoured and not deposit
• D. To calibrate flow meters

Answer: (C)

The main idea is to keep the flow in sanitary mains strong enough to mobilize settled solids. The minimum scouring velocity is the flow speed required to lift and carry sediments along the pipe, so they don’t settle to the bottom. When flow stays above this velocity, sediments remain in suspension and move toward treatment, keeping the sewer self-cleaning. If velocity drops below this threshold, grit and other solids settle, which can build up deposits, cause blockages, and lead to odor issues. That’s why the purpose is about preventing deposition, not about setting a maximum flow, choosing the pipe diameter, or calibrating flow meters.