MAINTAINING YOUR POND

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It's difficult, if not impossible, to repair a leak without draining the pond. However, determining the location of the leak may begin while the pond is holding water. Embankment ponds sometimes show evidence of leakage on the back side of the dam. Examining the outer bank may reveal especially wet areas or unusually tall grass or vegetation nourished by extra water. Another leak-locating technique is to dig a channel around the outside of the pond, at the base of the dam, with an additional ditch to keep the channel from filling with water. Examining the channel may reveal where water is leaking from the structure. Vegetable dyes are sometimes used in the pond water to help trace leakage. However, unless the dye reappears near the outside of the pond, the leak can't be pinpointed. Sometimes a "water witch" can dowse for leaks.

A little pond history helps leak detection. In the case of an embankment pond, find out if the dam was "keyed in." Good pond builders dig a core trench in the base of the dam and compact in a layer of impervious soil before building up the embankment.

Like a tongue-and-groove joint in carpentry, this key creates a solid bond between the base and the dam. It's also important that the base of the dam be stripped of vegetation before the embankment is built. If these two items were omitted, you have a pretty good idea where the trouble lies.

Ledge or a streak of sand may allow water to leak from the pond basin — straight down. There's no tracing that kind of leak with a channel or dye. The pond must be emptied, and even then you may have to guess exactly where the leak originates. Depending on pond design and terrain, the basin should be emptied by drain pipe, pump, or siphon hose. When the basin is empty, it may be possible to detect ledge or gravel patches that might be leaking. A foot or two of clay applied over the suspected flaw, harrowed in or packed with a roller, will often plug a leak. It's important not to dump the clay in a leaky pond, then refill it. The clay should be mixed with the basin soil and packed.

If good clay is available on site, it's the most economical solution. Otherwise clay is often trucked to the site. For those who live in areas where good clay is not readily available, bentonite is an alternative. Bentonite is a natural clay sealant that swells as much as 20 times its size when wet. It can be purchased in powder or granular form through aquacultural suppliers and well-drilling firms. Bentonite is generally applied "in the dry" at a rate of one pound per square foot. It is then mixed with the pond material with a light harrow and packed down. Simply dumping it from a rowboat into a leaky pond is not likely to remedy the problem.

Plastic or rubber liners are often used to seal leaky ponds. Liners are manufactured in various thicknesses, with optional ultraviolet-light resistance to retard decay caused by sunlight. Liners are popular in small water garden pools, golf-course hazards, and wastewater treatment lagoons. Because they cut off incoming ground water as well as leaks, liners are not usually used in ponds that depend on springs, unless only a portion of the pond is lined. When liners are used in spring-fed ponds, a drain may be required to prevent displacement of the plastic. Liners should be installed on smooth terrain, preferably sand, to prevent tearing. Another layer of sand is often used above the liner as further protection.

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