Hi,
Are you a student or an engineer? Don't duplicate post.
I misunderstood your drawing and went to the wrong direction, thinking no need for the pump.
The flow is from the pond to the tank, right?
The calculation is not different from other pump, except you have additional pressure due to the weight of the floating roof.
The discharge head should take into account the head loss of the piping, the entrance to the tank, the static head of water (max 14 meters) and the pressure of the floating roof expressed in meter of liquid.
For the suction head you need to consider the head of the liquid from the pump (suction lift) and the head loss of the suction line. level zero should be the pump center line.
note: No info about the flow rate.
Probably good to review Bernoulli and Darcy Weisbach equations.
Show us your work and we will be able to comment.
Terima Kasih
Good luck,
Breizh