In message , Simon Avery
writes
According to some (not all) of the books I've read about ponding,
using normal liners in saturated ground is a bad idea, and say the
liner will rise to the surface.

Personally I've got my doubts about that, given the weight of water
above it, and that the water is the same density above or below the
liner.

Simon

At my last house I built a 5m x 5m pond in a renowned clay area during a
drought.

Once it rained heavily, my liner lifted in waterlogged soils and
destroyed all the hard work.

It had to be drained and I put in a 2m deep 'soak away' lined with
gravel and led the ground water off into a distant ditch - this cost a
lot of money!

Just thought I'd add my tuppence worth.
--
Steve Jackson