New Liner in Sand-bottom Pool

[cjm52]

What is the best & safest way to fill a sand-bottom pool when installing a new liner. Installers generally want to use water trucks to refill pools after liner installs, but ours is an old sand-bottom pool and I'm concerned the force of water from the truck will disrupt the sand bottom. In our last install the bottom became badly deformed but I don't know whether the problem was the water truck or that there was some groundwater we could not remove before install. I don't want the same problem again. Is there a way to safely use a water truck with a sand-bottom pool?

[Denniswiseman]

I would be inclined to use a large sheet of 3/4 " ply with the corners rounded off and let them dump it on top spreading the load
The ply will then float to the top