Dam Liner Preparation

Dam Liner preparation for a geomembrane liner system:

Talk with Geoline about a suitable dam liner system.

Excavate Dam | Smooth Drum Roll Sub-Grade | Overflow / Spillway | Excavate Anchor Trench

Geoline Earthmoving Contractos

Excavate Dam: Use suitably qualified earthmoving / civil contractors to excavate your dam. Most dams that are lined have a slope of 2:1 , two horizontal to one vertical, however liners can be installed 1:1 or greater slope steepness. Slopes of a 2:1 are typically the steepest that you can have machinery work on easily.

Smooth Drum Roll Sub-Grade :The dam liner sub-grade finish surface should be a flat, dry, smooth surface with no protrusions. For best results please also remove any organic vegetation such as grass and weeds so that it doesn’t break down and give off a gas underneath the liner.

For extremely rocky sub-grade surfaces, you could put down a layer of sand first or thick geotextile to create a smooth base.

You need to have an overflow / spillway point installed in the dam, so that you can channel water away from the dam incase your dam was to overflow. This can be installed as a pipe penetration thru the liner or at the lowest point at the top of the dam edge. The overflow outlet will determine how much freeboard your dam will have. Freeboard being the vertical distance between the crest of the embankment and the dam water surface.

To secure the dam liner in place you need an anchor trench excavated around the top perimeter of the dam. The size and depth of the anchor trench will depend on what thickness the geomembrane is and what slope the liner is being placed on. Typical geomembrane anchor trenches are 300mm wide x 500mm deep. As a minimum you want to excavate the anchor trench 500mm back from the crest of the dam.

anchor trench design

For extremely large dams, we would recommend putting in some sub-grade drainage under the geomembrane liner system. This will help with any ground water build up or gas build up occurring under the liner.


Geoline can organise experienced earthmoving/ civil contractors to excavate your dam. Contact Us to arrange any dam liner civil works.