We've had to deal with similar situations several times. I'm assuming it is a horizontal drain pipe through the dam with an elbow and a vertical riser standpipe inside the pond designed to determine the full pond water level. I'm also assuming you don't want to completely drain the pond. You may be able to look down the riser standpipe with a flashlight and and see the leak. If it is along the vertical section of pipe, you may be able to temporarily seal the leak with heavy plastic film or liner material. If the hole is larger than a quarter, you will probably need to support the plastic with hardware cloth or screen of some type.

With the leak stopped you may be able to pump the pipe full of concrete from the back side. If you have a flange or can attach a flange to the back side of the pipe you can install a valve. The valve can be opened so the concrete can be pumped into the pipe and then the valve can be closed to contain the concrete while it sets up.

We often siphon the water level down at least 4 feet or below the leak. If done when the water is cool, the fish can still survive. We cut off the old pipe and fill with the elbow area of the drain with concrete mix (you might have to pour some concrete in, let it set up and add some more until water will not flow through the pipe) from the top. We then install a new pipe through the dam. The new pipe is installed in as shallow a trench as possible. We want the new drain to have an elbow and very short riser standpipe. Concrete is poured around the elbow to help seal and stabilize the new drain. The riser allows the full capacity of the horizontal drain pipe to be utilized with even a couple of inches of rise in the water level above the top of the pipe. A horizontal pipe alone would allow much less water to be discharged since only the bottom of the pipe would be wet. It is very important to compact good clay soil carefully around the pipe as it is buried. The shallow trench is less likely to leak since there is less water pressure and the rest of the dam is undisturbed. If the water level needs to be lowered sometime in the future, it must be siphoned (or pumped), but the repair is less risky.

The slip liner described earlier will work well if you can get access to both ends of the horizontal pipe (assuming you don't have a vertical riser standpipe or are willing to drain the lake to cut the standpipe off). You must seal both ends of the slip liner's connection with the old drain pipe.

I hope this isn't too hard to understand. It's hard to describe without being able to use my hands to demonstrate.


Johnny Foster
Foster Lake & Pond Management, Inc
919-772-8548
www.fosterlake.com