I found this forum when I was Googling to see if anyone has buried a water storage tank as a koi pond. There was a post in 2008, but the content was mostly about the pipework.
What I want to know has anyone done it, and can the sides of the full tank take it? I am envisaging using the higher diamter size (2.6m) cut off at about 1.2 - 1.5 m, with anywhere from 250 - 450 mm above ground - depending on the final design. The above ground part will be protected by either a wall or a rockery/waterfall.
Separately, I am also researching using an EPDM flexible liner. The probelm is that I have limited space, and so I need near to vertical sides to get volume and depth without dramatically increasing the width. From what I have found so far, it is inadvisable to have more than 30 - 60 cm vertical sides with these liners without having additonal brick or concrete soil reinforcement. Otherwise there is a chance the soil moves and drops down behind the liner causing bulging - and maybe then losing the edge of the pond. I've thought of using vetically stacked 'Terraforce blocks as reinformaent (as cheaper alternative to having a 250 wall buiilt) but this still has an oncost.
So, if anyone out there has either buried a plastic tank, or has used EPDM nearly vertically without reinforcement, I would love to hear about it.