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.
- 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
Horizontal Distance X (cm)
Vertical Distance Y (cm)
Pipe Diameter (cm)