buoyancy calculation for PVC Liner

[112Octane]

Hello
Does anyone have any guidance on determining the buoyancy of a PVC liner in a pond with a high groundwater table? I'm looking to determine the amount of fill or ballast required over top of the liner to hold it in place during the seasonal high.

 

[TDAA]

Volume of displaced H2O times 62.4 pcf to get the boyant force.

Thickness of fill above liner (in area below water table) times area of the fill below the water table times the density of the in-place fill.

They should at least be the same. Increase thickness for a factor of safety.

Alternate: Have some holes in the liner to equalize the pressures =P