Fixing A Leaking Pond

During wet periods like we’ve had this winter, most of stock ponds are brimming full of water, but when the warm dry weather arrives, will that pond still be holding water?  Pond leaks are a very common problem in South Central Texas. Some leaks may be barely noticeable, while larger leaks can completely drain a pond. Unfortunately, fixing a leaking pond can be one of the most difficult problems associated with managing a pond.

There are two main areas were most ponds leak, the pond bottom and the pond dam.  The most common cause of ponds leaking from the bottom occurs when areas of sand or gravel or fractures in bedrock that were not adequately covered with soil during construction.  Leaks around the dam are typically the result of allowing trees to grow on or close to the dam.  The tree roots will grow into the dam itself causing a leak to develop over time.   In older ponds, leaks sometimes develop from outlet pipes that rust and leak below the water surface.  Leaks that occur on the pond banks or on the dam are sometimes easy to locate, water leaving the pond may emerge on the outer surface of the pond, providing a clue to the location of the leak. Wet areas and growth of water-loving plants (like cattails) at the base of the pond dam or banks may be clues to the location of these pond leaks.

The best method for sealing a leaking pond bottom will depend mostly on the type of soil that exists on the pond bottom. Of greatest importance is the mixture of large (sand or rock) and small (clay or silt) particles within the soil. A soil scientist from the Natural Resources Conservation Service (NRCS) may be able to assist with soil characterization. If the existing soil is too coarse (i.e., too much sand or gravel), clay can be added to provide a better seal. Bentonite is a type of clay that can also be used to plug pond leaks as well. When bentonite gets wet, it swells to many times its original size and fills cracks and pore spaces to effectively seal the pond bottom.

Plastic or vinyl liners can be used in most conditions to seal a leaking pond. They are used most frequently on small ponds or where severe leaks occur repeatedly. These liners can provide a watertight seal under the right conditions, but they are expensive compared to other techniques. Proper installation, especially in joining the sheets together, is critical to ensure their effectiveness.

It is very difficult to generalize the cost of repairing a leaking pond. Many factors can affect these estimates. Replacement of a rusted outlet pipe or sealing a small leak near the top of the pond may be inexpensive. However, draining the pond and sealing the entire bottom may cost thousands of dollars. The use of local clay will be inexpensive compared to bentonite, which may cost $50 to $100 per ton without hauling costs. Plastic liners are often the most expensive alternative at approximately $25 per square foot or more.

For more information on sealing leaky ponds, contact the Texas A&M AgriLife Extension Service of Austin County at (979) 865-2072, or visit our website at:  http://austin.agrilife.org and click on the Ask the Agent Tab.