What is the minimum flow needed to obtain a scouring velocity in a sewer line?

What is the minimum flow needed to obtain a scouring velocity in a sewer line?

• A. 1.2 ft/sec
• B. 12 ft/sec
• C. 5 ft/sec
• D. 2 ft/sec

Answer: (D)

Scouring velocity is the flow speed needed to keep solids moving so they don’t settle and form deposits in the sewer. If the flow is too slow, sediments settle and reduce capacity; once you reach the scouring velocity, the solids are mobilized and carried along. For typical sewer sediments, this minimum mobilizing speed is about 2 ft/sec (roughly 0.6 m/s). So the minimum flow to achieve scouring velocity is 2 ft/sec. A slower flow would lead to deposition, while faster flows are above the minimum and aren’t required to meet the threshold.

Scouring velocity is the flow speed needed to keep solids moving so they don’t settle and form deposits in the sewer. If the flow is too slow, sediments settle and reduce capacity; once you reach the scouring velocity, the solids are mobilized and carried along. For typical sewer sediments, this minimum mobilizing speed is about 2 ft/sec (roughly 0.6 m/s). So the minimum flow to achieve scouring velocity is 2 ft/sec. A slower flow would lead to deposition, while faster flows are above the minimum and aren’t required to meet the threshold.