Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? I saw this red clay pipe...

Sooooooo, his pond excavation pierced an old clay drainage tile, which presumably is slowly leaking water out of the pond, probably (but not, I believe necessarily) on a downhill side. This problem has two parts, locating the intersected tile and stopping water flow through it.

1) Location:

I assume the guy doesn't remember where the tile was, or you wouldn't have to worry about location. You basically have an Archaeology problem - locating a man-made artifact buried in the ground many years after it disappeared.

You may be able to find the drainage tile from an above ground search. These clay tiles were hand-fitted together in their ditch, often with intersections made from straight pieces rather than with pre-made tees or elbows. The overall result is that they usually have a fair number of cracks, bad joints, and mis-matched sections where surface water has washed topsoil into the tile, making holes ("blowout holes" in the vernacular common to my locale). A drainage tile line can often be located by noting where a series of holes fall in a line (straight or possibly curved) in a field which is otherwise mostly hole free. If the blowout holes are big enough, the tile can be seen in some of them, allowing positive identification. "Connect the dots" with the holes to trace the probably line of the tile to the pond; that would be the place to center your subsequent subsurface search.

Tile lines also may be spotted above ground by a line of settled dirt that is lower than either side; this is where the ditch that the tile is in was refilled and then dropped down as the soil later compacted. Both the settled ditch and blowout holes will be easiest to spot in a closely-mowed grass field. If they are in a plowed field, they may not become apparent again for some time after plowing (after more dirt washes in to the holes in the tiles). They can be spotted with a little more difficulty in wooded areas (Brettski has some picks of blowout holes in his woods).

Like many subsurface features, drainage tile lines may be more easily seen from aerial photography. Low sun angle (early morning or late afternoon) may be the best times to see the shallow depression where the ditch has settled.

If the tile cannot be detected at all from above ground, a shallow search trench around the perimeter of the pond should detect it even if it does not dig down deep enough to intersect the tile itself. The disturbed dirt from backfilling the trench will have different color/texture than the native soil layers. IIRC Mike Otto had a good picture of the disturbed soil on an old trench line in a recent issue of PBMag.

2) Blocking the tile:

My first pond had an 8" clay drainage tile running through it's location before we excavated. The upper end of the tile was run into a length 10" PVC pipe where it entered the pond (with a varmint-guard in it to prevent critters from crawling up into the tile and blocking it), and then a bed of fist-sized limestone was placed below the outlet to prevent erosion from water coming out of the tile in times of low water (the end of the tile is about 1.5' below full pool).

Where the tile exited the pond basin, it was cut by the core trench which went much farther down than the shallow tile. Regular clay compaction of the core trench served to prevent any pond water from entering the tile below the dam.

Once you find where the tile leaves the pond, a mini-core trench cut down below the bottom of the ditch the drainage tile was placed in (and wider than the original ditch), backfilled with good clay and well compacted as it is backfilled, should seal off leakage through the old tile. I think for a project of this scope a backhoe and a jumping jack compactor would be sufficient.