One of the larger frustrations a pond owner can have is a leaking pond. That is the purpose of a pond anyway, to hold water. When it starts retreating and you realize that it is more than evaporation, it can be difficult to find and solve the problem.
When a pond loses significant amounts of water on a regular basis, even if it is temporarily recharged with rain, there is a profound effect on the pond and how it functions. Vegetation proliferates in the marginal areas along the shore. Facultative plants that enjoy a zone from damp ground to 18 inches of water now have a larger zone where they can flourish due to the fluctuation in water levels. This can contribute to filling in the pond around the edges, in addition to choking the pond with unwanted vegetation.
As the pond loses water, it functions as a smaller pond and that is more challenging for water quality. Nutrients are concentrated and the lower volume of water heats up and cools down more rapidly. This can stress fish and cause more algae growth.
Fish have less access to habitat and they are more concentrated. Crowding affects fish, and with reduced water quality, this could also result in stunting or imbalance between bass and bluegill populations.
In the summertime, when the sun is blazing down on everything, including the water’s surface, it is difficult to tell the difference between a leaking pond and losses due to evaporation. If you suspect a leak, place an open 30- or 55-gallon drum in the pond and fill it with pond water to exactly the same depth as the pond. Monitor the water level in the pond and the drum. Evaporation should remove the same amount from both the pond and the water contained in the drum. If the pond retreats faster, then more than evaporation is removing water from the pond.
Causes of Pond Leaks
Construction must be done correctly from the beginning and if you are constructing a pond with an earthen bottom, this means 18 inches of clay packed with a “sheep’s foot roller.” This machine’s large roller has protrusions that knead the clay and makes a durable seal. Machines on tracks or tires will not pack sufficiently.
Wildlife such as crawfish, nutria, or muskrats can burrow into pond dams and cause small leaks that later turn into large ones as water erodes along the initially developed channel.
I started managing ponds in South Carolina in 1996 and the first five years were short on rain. I fielded lots of phone calls from pond owners with “spring-fed” ponds that were losing water fast. If your pond is “spring fed,” then it is directly connected to a dynamic water table that can change over time. When the water table drops, you can add water but it quickly disappears into the water table below. A constructed, sealed pond, fed with surface water runoff will not experience this issue.
Discourage trees from growing along the dam of your pond. Tree roots can develop channels where water can escape. Dead tree roots can rot, and storms can tear out trees, causing a dam failure and complete loss of the pond. “Dam” probably won’t be the only word you use when this happens.
Spillway structures should be built with high-quality materials and durable construction to last 20 years or more. A cement collar around the pipe can avoid channeling leaks along the pipe in the future. A fish farmer and experienced pond manager taught me a trick to temporarily repair a small leak in a spillway. He used a piece of couch cushion padding stuffed in the hole which, when tightly packed, turned a gush of water into a drip. Always use caution when working around spillways, especially ones with damage. Water flow is powerful, and if a spillway is showing wear and damage, then more damage could occur while you are trying to repair it.
Bentonite is a fine clay that swells on contact with water and is useful in spot treating leaky ponds. In Indiana, I have seen pond owners fill crawfish “chimneys” with bentonite to clog the tunnels made into the dam. More commonly, it is used as a spot treatment in a suspect area along a dam or in the floor of a pond. Bentonite is broadcast and tilled in to the area. The results are variable.
More and more farm and recreational ponds use liners. While they can add significant expense to pond construction, the results are assured. The liner can be trenched in to secure it around the perimeter and soil and gravel can cover the edges. Covering the edges gives a natural look and also keeps access around the edges safe, since liner materials can become, literally, a slippery slope.
After realizing the pond wasn’t properly constructed with a clay liner, a clay liner can certainly be added after draining and drying the pond enough for construction.
Farmers in Tennessee, and I am sure other areas, use pigs to seal a pond. They fence off the pond and turn the pigs in. As the pigs march around in the pond and wallow in the mud, they knead the clay liner back together.
Many pond owners will add well water. Well water is cool and low in oxygen. Splash it, spray it, or run it over rocks or other material to break it up and increase the oxygen. You may want to consider adding aeration or operating existing aeration more often to maintain good water quality while water levels are low.
Again, a leaky pond can be frustrating, so keep a clear approach. Investigate and test before investing time energy and money on fixes. When building a pond, sealing it correctly from the beginning will avoid this frustration altogether.