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California Pipe Flow Metering Method

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With the California Pipe Flow Metering Method the discharge from the open end of partially filled horizontal pipes discharging freely into the air can be measured.

The discharge can be calculated as

q = 8.69 (1 - a / d)1.88 d2.48                           (1)


q = discharge (ft3/s)

a = distance in the plane end of the pipe - from the top of the inside surface of the pipe - to the water surface (ft)

d = internal diameter of pipe (ft)

The equation is empirical and can be used for pipes in the diameter range 3 - 10 in

  • 1 mm = 0.00328 feet
  • 1 ft = 0.3048 m = 12 in = 0.3333 yd = 30.48 cm = 304.8 mm
  • 1 ft3/s = 0.0283168 m3/s = 101.9 m3/h = 28.32 dm3(litre)/s = 60 ft3/min = 373.7 (UK)/min = 448.9 gal (US)/min (US gpm)

California Pipe Flow Example

In the discharge on a horizontal 4 inches PVC sewer pipe the distance from the top inside pipe to the water flow is 3 inches (0.25 ft). The inside diameter of the PVC pipe is 4.069 in (0.34 ft)

The discharge can be calculated as

q = 8.69 (1 - (0.25 ft) / (0.34 ft))1.88 (0.34 ft)2.48      

   = 0.049 ft3/s

California Pipe Flow Calculator - Imperial Units

California Pipe Flow Calculator - Metric Units

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