Pond Boss Forums POND CONSTRUCTION Building a dam cutoff trench, or core trench after the fact

There needs to be a continuous impervious wall keyed into an impervious underlying base layer to keep water from leaking. A new dam behind an existing dam can be created, but the water level in the existing pond will make creating a new dam more difficult because of the hydrostatic pressure it puts on the leak. I cannot speak to the use of plastic or liners because I am not familiar enough with their use. If the water can get down to gravel, then it can leak out. Gravel layers can be sealed with a continuous clay liner, but water must be prevented from reaching the gravel. A complete continuous seal up to the full pool level is needed to maintain water level. I have personally installed a core trench in the dams and lined the complete bowl with clay on my three fish ponds and half dozen wetlands. The new pond is not yet full, but the rest hold water very well. The new pond has not gone down yet, but it needs another 4' of water to reach the overflow pipe. If you can drain the pond, you could core behind the existing dam down to good clay, and then use the old dam soil to top it off above the full pool level and behind the new dam. Folks use different terms for the same thing in different places. I just wanted folks to chime in and help you out. Having built my last pond alone, I know how hard it can be not to take shortcuts. This forum has ben good for keeping me honest while building new ponds. I still hope to build another 3 ponds before I kick the bucket.