Drainage beneath pond-liners

Drainage beneath a pond liner is necessary in the following circumstances:

• When water is likely to flow beneath the pond membrane
• When erosion might take place beneath the membrane
• When organic matter is present beneath the membrane, and might generate gas
• When changes in the groundwater would exert pressure on the membrane

Perforated pipes, laid to falls and protected from sediment by geotextiles, can be used for either water drainage or gas drainage. Drained water must be discharged downwards and drained gas must be discharged upwards.

• Under-pond drainage can protection against (1) a rising water table [top], (2) rising methane from the decomposition of organic matter [middle] (3) lateral pressure from a high water table [top]