Geomembrane Liners for Dams and Ponds
One of the most common geomembrane applications is as a pond liner. Pond liners may be used where:
- The subgrade conditions do not allow a cut to fill pond to hold water.
- The subgrade materials are dispersive and this interferes with the end use of the water.
- Liquids other than pure water are stored and it is required to minimise the escape of the contained liquid. An example of this is sewerage effluent where the entry of small amounts of pollution to subterranean water supplies may have health implications for downstream users.
- It is required to minimise erosion on the pond embankments. Erosion may be caused by the impact of rain or by the effect of aeration or mixing equipment within the pond. An example of this is the use of lining systems on prawn grow out pond embankments to minimise the entry of suspended sediments into the pond and the associated increased risk of disease and crop loss.
For more information regarding the use of geomembrane applications for pond lining.
Liquids that are contained may be drinking water, industrial process waste such as dunder or mine washings, sewerage or molasses.
The subgrade that is to receive the liner requires careful preparation. The subgrade preparation is required to meet the specification of the liner manufacturers. Failure to meet these requirements may result in the invalidation of the any offered guarantees. Typically the embankments are required to be regular and free from sharp or large rocks. Material placed in contact with the liner is required to be less than 10mm in size. Where granular material forms the subgrade it is usual to place a geotextile under layer. The geotextile used is usually a needle punched, non-woven material with a weight of not less than 250gms/m2.
Where ponds are to be constructed in areas where there is vertical gas movement through the subgrade of the pond then it is required to provide a subgrade venting system to prevent gas collecting below the liner. Vertical gas movement may be produced by the movement of the water table over a seasonal or diurnal period or by the degrading of vegetation matter at depth. The venting system usually consists of a full geotextile layer underlayed by a herringbone system of slotted pipe or slot drain wrapped in geotextile. The venting system may fulfill a dual roll. The system can double up as a leak detection system and can also be used to monitor the level of the ground water before the level of the contained liquid is reduced to minimum levels.
Lining materials for ponds include HDPE, Polypropylene, Elvaloys and PVC.
The most widely used lining systems are HDPE,
which is produced in various thicknesses and textures. HDPE is delivered in 7m rolls weighing approximately 1.6 tonnes. The material is unrolled and welded on site with wedge and extrusion welding equipment.
Lining systems are anchored at the perimeter of the pond by either burying the upper edge or by fixing the perimeter to a concrete anchor beam.