While this is not intended to be an exhaustive guide on dam construction and liner installation it will highlight some of the more important facets

Project design

Savings can be made on both the excavation and liner costs if the design is kept to straight lines, eliminating curves.

If you wish to keep back fill in place then batters should be no steeper than 3:1

Dam Construction

If the excavated site has good top soil, sand, etc. for use as liner overlay a stockpile should be made nearby for later re-use.

All injurious materials such as tree trunks, roots, rocks or sharp protrusions should be removed. The dam surface should then be rolled.

A trench will be needed around the entire perimeter of the dam in which to anchor the polyethylene lining. It should be approximately 400mm deep and 350mm wide at a minimum level of 500mm above the projected water line.

Laying of the Polyethylene Liner

Before laying the polyethylene sheet it is advisable to check that all sharp elements that may cause damage are removed. The dam surface should be reasonably dry and certainly free from standing water.

If the liner is to be fully covered with backfill then this should be to a level of about 300mm.

The liner should be laid as quickly as possible to avoid damage from wind and rain which could retard the completion of the project.

If conditions are hot then it is advisable to install during the coolest time of day. This is due to the fact that polyethylene expands and contracts and therefore it is preferable to lay and seal in the contracted condition.

Backfilling

The backfill material should be end dumped over the liner and then leveled with a bulldozer or other suitable equipment. Heavy equipment should never be allowed directly on the liner and any sharp turns while over the liner should be avoided.

Total backfilling of the dam is not essential but does give the liner extra life against UV, especially where the liner is exposed. This is usually near the top water level of the dam.

Below is one method of soil covering the top of the liner, without the need to cover the entire dam.

Backfilling should also include filling the anchor trenches.

Joining and Sealing

The best method of sealing polyethylene is a continuous weald. This can be done by use of a wedge or hot air welder. Each method involves overlapping the sheets and necessitates skilled and trained personnel

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