|Thursday Techniques: Pond Liners|
|Written by Heleigh Bostwick Thursday, 09 August 2012|
When you construct a pond, it’s necessary to use a pond liner, whether it’s a type of plastic such as polyvinyl chloride (PVC) or high-density polyethylene, or a layer of bentonite clay. Pond liners line the pond forming an impervious barrier between the soil and the water so water doesn’t seep into the soil.
Environmentally speaking, the choice of liner would naturally be bentonite clay, even if the pond is quite large or very small. There are two types of bentonite clay, sodium bentonite and calcium bentonite but only sodium bentonite swells on average to approximately 15 times its size when exposed to water. During the swelling process, the clay forms a tight bond with the underlying soil.
As a clay soil, bentonite is naturally impervious but does have its problems if the clay layer, typically 2 to 4 inches thick, is not properly compacted during the construction phase. Clay particles are very fine and wind during storms can cause the clay to become re-suspended. When this happens the water becomes murky, which is not just an aesthetic problem; it can cause problems if you are trying to grow aquatic vegetation or create a pond ecosystem complete with fish.
A word of caution however; when dry, bentonite shrinks back to its original size so it’s not a good option if your pond is seasonal and dries up in late summer or during droughts. The rate and method of application is also dependent upon an analysis of the existing soil type.