Wastewater math
Flow, area and velocity in an open channel.
The formula
velocity = flow ÷ areaWPI Formula/Conversion Table (2023), Printed page 3 of 10, Flow Rate, ft³/sec: Area, ft² × Velocity, ft/sec
area = flow ÷ velocityWPI Formula/Conversion Table (2023), Printed page 3 of 10, Flow Rate, ft³/sec: Area, ft² × Velocity, ft/sec
flow = area × velocityWPI Formula/Conversion Table (2023), Printed page 3 of 10, Flow Rate, ft³/sec: Area, ft² × Velocity, ft/sec
Worked example
A channel carries 12.5 ft³/s through 10 ft² of water-filled area. What is the velocity?
area 10 ft², flow 12.5 ft³/s
Find velocity in ft/s.
Feet, square feet, cubic feet per second, and feet per second form a compatible unit set.
The water-filled cross-sectional area is already given as 10 ft².
Velocity = flow ÷ area.
12.5 ft³/s ÷ 10 ft²
12.5 ÷ 10 = 1.25 ft/s.
The resulting unit is ft/s, which matches the question.
1.25 ft/s
Answer: 1.25 ft/s
Practice
Practice this math in the Math Center, with hints and worked steps.
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