(Go to the bottom of this post for the hole if you don't want backstory)
About Dec 2017, I had this pond dug renovated (it never held water before) by a local excavator that digs ponds, I assumed he'd do it "right" and I couldn't find any other options so I went with him ( side note, I'm amazed I can find no reputable companies around here that do this). The biggest thing he did wrong, as pointed out by Pond Boss alumni, TJ (who is freaking awesome by the way, so much knowledge...) is he used the treads on the dozer to pack and did not use a sheepsfoot roller to pack the clay. He in fact did all of the work with the dozer.
December 2017: image broken
almost full by February 2018 you can see the black drain pipe on the left, I was super excited by this point. image broken
down ~8 feet by July 2018, much less excited. image broken
The pond never dried up but kept fluctuating with the rain, this is September 2019, I pumped it nearly dry, see what I discovered below the photo.
(end of backstory)
The culprit has revealed itself. I found this hole, and then one smaller about 10ft from this. This hole is not on the dam side, it's actually on the opposite side of the pond from the dam.
I've had several contractors out to look at this, now keep in mind, these guys are like Jim-Bob from back in the hollar who just happen to do dozer work for a living, so they aren't what I would consider experts. One suggestion was rebuilding the entire dam and digging the dam down deeper, another was to go find clay somewhere nearby on my property and repacking the pond in about 2ft of clay, and yet another was to put a liner in the pond and covering the liner in clay. Someone else said dig down find the rock seam and blast it, this one sounds the most fun :p . These all sound super expensive.
How would you suggest attempting a fix, have any of you seen a hole like this develop? what did you do? Here are some of my cheaper ideas. -I could fill it full of sodium bentonite + pray. -I could pour soilfloc down in it and let the next rain carry it on into the hole (hopefully plugging things) -Dig down with a track hoe, exposing the issue, repack it with clay -or- determine another option once I see where the water is going.
The hay is a good way to go when looking for a bridging agent to seal off seepage in a big hole . I would break up the bales though. Add all the bales you can get in the hole and then add a lot of bentonite on top of it all. One way to look at it is to consider the hay as a fiber material. If you ever played pixie sticks and dropped them in a pile on a table, that is what a bridging agent might look like. And then do a very thick cover of bentonite to seal off the small holes in the pixie sticks. If the hole is large enough you might try doing all this in layers.
Wouldn't the hay rot away after a couple of years and allow the hole to open up again? I think geotextile with gravelly "parking lot" clay over it, then bentonite over that might be a better option. Just an opinion.