Properly installed, a liner is 100 percent effective in stopping seepage. For soils with high gypsum content, a liner is the only option. Because of the relatively high cost, liners have been used primarily for ornamental ponds, water storage, fish hatcheries, and research facilities.
However, advances in liner technology achieved through their widespread use for landfills, hazardous waste, and water storage facilities have caused prices to fall. Proper liner installation is important.
A liner’s edges usually are anchored into a trench built around the pond perimeter. Many factors influence the selection of a liner material, and consumers have a wide choice of products. Modern plastics are environmentally safe, withstand freezing, and are UV-stabilized for long-term exposure to the sun.
With care, a pond liner can last 20 to 25 years. Liner thickness is measured in thousandths of an inch (mils). Twelve- to 20-mil liners can be used in sandy soils, while thicker liners are required to prevent punctures in rocky soils.
In some cases, an inexpensive geotextile mat is applied under the liner to protect against punctures. Liners 20 mils or less in thickness are more suitable for temporary uses. For permanent aquaculture facilities, 30- to 40-mil liners are recommended.
Thin liners will be punctured by plant sprouts along pond edges unless a sterilant is applied before the liner is installed. Obviously, even thick liners must be protected to a reasonable degree. For example, cattle should not be allowed to trample lined ponds.
Liners can be made from highdensity polyethylene (HDPE) or low-density polyethylene(LDPE). LDPE is more flexible and is used where there is more shifting or movement of the soil, while HDPE is more resistant to chemicals.
Polyethylene is both economical and durable and can be fiberreinforced for greater strength. Seams on polyethylene liners are best sealed by heat welding or extrusion, which calls for custom fabrication for smaller ponds or professional installation on larger ponds.
Vinyl can also be used for liners and, though less resistant to aging than polyethylene, it can be sealed and patched with solvent adhesives. For smaller, ornamental ponds, butyl rubber is typically used as a liner material. A proprietary, liquid urethane rubber product is also available.
It conforms to any pond shape and seals around pipes and other structures. Professional installation is recommended but gallon kits and an instructional video are available to homeowners.
Liners will become slippery with time, which can create a safety hazard where pond slopes are steep. Using a textured plastic liner, or embedding small stones in the liner’s sides with a liquid urethane rubber product will provide a non-slip surface.
Other Treatments:
Other methods of sealing ponds include the use of animals, puddling, and gley (organic matter). A traditional remedy has been to fence pigs, cattle or other animals in the pond basin. Livestock manure aids in sealing the pond bottom, and animals trampling the pond bottom compacts a deeper layer of soil.
This method gives mixed results and can cause nutrient pollution of surface or ground water until the pond seals up. Puddling refers to the deliberate churning of soupy wet soil. Fines released from the soil during the mixing form a barrier of low permeability as they settle out on top of heavier particles. Soils must contain some clay and silt particles in order for puddling to work. Puddling forms a seal that has little strength, so it is not suitable for thin soil layers over rock.
Puddling is used primarily in small dugout ponds or to create zones of low permeability within larger dams that are otherwise constructed to structurally support the weight of impounded water.
Burying a 6-inch-thick layer of organic matter, typically straw or a manure-straw mixture, in a pond bottom has been used as a sealing method. Once the organic matter is spread over the pond basin, it should be covered with soil and compacted firmly.
Microbial action converts the material to a “gley,” an organic layer of low permeability. This method does not form a seal quickly and unwanted nutrients might flow into surface waters until a seal is formed.
Prevention:
Proper site selection and pond construction methods will help prevent pond leakage. Landowners should consult with the Natural Resources Conservation Service before building a pond. The Service has soil surveys with valuable information on soil properties and their suitability for water management. Taking core samples from a proposed pond site will help identify areas of high permeability and prevent future problems.
Cutting too deeply during construction is a common cause of leaky ponds. As adequate compaction and suitable moisture content are critical, a pond basin should be in the middle layer of a soil profile. This middle layer is called the B horizon and typically has the maximum accumulation of clay. The parent material underneath the B horizon may have little clay.
Finally, pond maintenance is important in preventing leaks from developing. Levees should be mowed to prevent tree growth and to discourage burrowing animals. Trees growing on levees are a frequent cause of leaks in older ponds. However, once trees with substantial root systems become established it is better not to cut them down, as leaks typically develop where dead roots decay.
Author:
Nathan Stone
