Estimate discharge from a pumped well/tubewell via trajectory free-fall or jet-flow method.


  • Measure the inside diameter (D) of the pipe accurately, in cm
  • Measure the distance (X) that the jet flow of water travels, in cm parallel to the top of the pipe (fig. 1)
  • Measure vertical drop distance (Y) in cm
  • Estimate tubewell discharge by substituting values in online tool


  • This method provides a simple, inexpensive, and practical means of estimating flow from horizontal and inclined pipes for field tests.
  • No special training is needed to use this method.


  • This method provides only an approximate discharge from wells with horizontal or inclined pipes.
  • Well flow should be constant. The top of the stream at the open end of the pipe should not vary appreciably.

Method Limitations

  • Under ordinary field conditions, with reasonable care, measurements can be made in which the error seldom exceeds 10 percent.
  • The most accurate estimated discharge will be obtained
    when the pipe is truly horizontal.
  • The discharge pipe should be a straight length of standard pipe at least 5 feet long, so that the open end is at least this distance from the nearest elbow or bend in the pipe.
  • If the discharge pipe slopes upward, the estimated discharge will be too high; if it slopes downward, the estimated discharge will be too low.
  • The principal difficulty with using this method is in measuring the coordinates (X and Y) of the jet-flow stream accurately

Online Calculator

Horizontal Distance X (cm)

Vertical Distance Y (cm)

Pipe Diameter (cm)

Discharge (liters/sec)
Tubewell discharge from horizontal pipe
Fig.1 Discharge from Open Horizontal Pipe
The online tool is based on above equation