Pond Boss Forums POND CONSTRUCTION Building a dam Core trench depth??

I make sure mine are dovetailed a few feet into an impermeable soil layer that hopefully extends under your pond. That layer may start just below the topsoil or may be too deep to reach. This does not depend on if your pond is a 2' deep wetland or a 20' deep pond. The water needs to be blocked from getting out of the body of water by the core trench. The depth of the water does affect the pressure exerted below the water surface and the width of the trench needs to be wide enough to account for that water pressure. Test holes should help determine your particular geology.