Lesson learnt: in all O&M tailings management manuals put in a requirement to observe the penstock more carefully when tailings discharge water is not going through it—look carefully to see if water from another source is exiting the pipe and find out why.
This is a new lesson learnt. This is something I had not before now thought of. But on the basis of what I saw and did today, a necessary action.
Add it to your O&M manual.
Here are some pictures of this situation:
If you have a penstock and seek to know more, contact me.