We just bought this property under a year ago. And we knew there was a leak but didn’t know it was this bad. We think a muskrat dug a hole and eroded away enough dirt under the dam that it uprooted a tree and created a gaping hole in our dam. Where the hell do I start here. I need your help. I have a John Deere 1025R with a backhoe and bucket attachment. As well as a John Deere gator. Do I dump stone in steel fencing crates and place them in the hole and back fill with soil and a layer of bentonite clay on the inside? Any suggestions would be great. Thanks. PS. The last photo is after a huge rainstorm. It was running like crazy.

After you fix your current problem. You will have to deal with all the trees on, near and downstream of your pond.
Even a quick google search will tell you it is a no-no.

You might have to divert as much water as possible that is flowing into your 'pond'.
And then build a NEW DAM diwnhill or uphill of the current dam.

I dont blame you for the current trees on the dam. But with all those trees on your dam, even if you fix this current hole another one will pop-up in a no time again.

If for some reason you don't build a new dam and only repair this one.
Then the 1st step would be to stop the current water erosion by lowering the pond level to below the hole in the pond:
1) Electric/Gas Pump to pump out the water faster than it is coming in
•) Deepen and possible widen your overflow so that water doesn"t make it up to the hole in the dam
•) Divert water before it makes it into your pond with ditches or swales  etc etc

I like you gabion retaining wall idea alot use that for the new dam as well too

Trees will create holes

Proper dam walls have clay cores which prevent water seeping through the wall.
You may be lucky and find a plant operator who can help with a rebuild, but check their work out first.
Some will take your money do what looks right, but its not.
Depending on how long and deep your wall is, a proper repair at the break may be possible, other wise, as suggested a new wall may be necessary.

In a beloved Disney recording from my childhood of Winnie The Pooh, Eeyore has this to say upon seeing the fallen tree in which Owl had used to reside:

“If you ask me, which nobody did, when a house looks like this, it’s time to get another one.”

I have no actual useful knowledge or expertise to offer but my sense of dismay on seeing your photos is well-captured by Eeyore’s dismal comment. What you got there looks more to me like something that USED to be a dam.

Welcome!  Looks like a challenge.  What is your ability to control the water level behind the dam?  Do you have an overflow and/or sluice gate?  That will be critical to both repair and ongoing maintenance, particularly if you are picking up a lot of rainfall at times.  Good luck and keep us posted as to your progress!

I have a similar project with an empty pond and a breach in the old dam that bypasses a cement wall containing a drain pipe for draining the dam back in the day. We don’t know exactly what caused the damage that led to the erosion of the sand berm that constitutes the dam, but suspicion is a logging operation back in the 70’s used the dam to skid logs off the property, damaging the vegetation, leading to erosion from rain over time.

The stream that feeds the pond originates approximately 6,000 feet SW of the dam in a swampy area. It is a spring fed, year around stream, two of the spring weeps occuring on either side of the historic pond area that originally was a small valley, part of a series of such valleys in the sandy area from the foothills to the west that fan out towards the Hudson River flats to the east. The presumption is these valleys originated from the repeated outflows of the prehistoric glacial lake Albany when the glacial ice dams failed. The original path of the stream that entered the drain pipe has diverted into a new path some yards over and passes through the breach in the sand dam. This gives me the opportunity to restore the drain pipe in the cement wall and install a replacement sluice gate. Afterwards the stream can be diverted back to its original course, passing through the open sluice gate and allowing work to repair the breach.  In addition to the replacement sluice gate I will need to install a replacement overflow pipe to prevent water from overtopping the dam during high water events. Rather than have the water drop into the low drain pipe such as originally configured (I remember the sound of the water dropping into the pipe as a child while swimming in the pond) we are thinking having the overflow flow across the dam and exit above the low side of the dam, allowing for a waterfall and possibly micro hydro projects.

In the situation the OP has with his breached dam, I would suspect building a temporary coffer dam would allow repair to the breach, but as has been pointed out trees growing into the dam can cause additional problems. It’s hard to evaluate how large the pond is and how large a volume of water is impounded or what the source of the water is.

One often touted resource for dam expertise is the is the Pond Boss forum that I recommend highly for advice for situations such as the OP is experiencing.

I have been emulating my local beaver friends . I cut some large and small trees, lay them across the flow, and add rocks , gravel, mud, sand, more wood, and clay, here and there. I have built about 5 dams in a creek that is a raging flood each spring and the water seeps a little but is slowly plugging itself with my help.

A couple of pictures of my dams can be seen in my project thread.

Pics from the other side would be helpfull. It looks like the water level is way too high in relationship to top of dam, but the pic can be deceiving.

If this is the case, looks like there is no spillway or the spillway is not designed right. Cant tell from what you posted.

With the equipment you have, the repair can be made. But id take a moment and figure out the entire operation of the pond and change what is needed.

Nicholas, I second what Miles said.  Learn everything you can about beavers and how they make dams.  They are amazing, they are some of the best engineers we've got.  Some of their dams have lasted for our generations, not to mention their generations.  

It wouldn't hurt to get a hydro engineer out there to give you a consultation and some ideas.  My dad had the same kind of situation with a creek that would flow at about the speed and volume of your fastest photo, into a pond he dredged out, and he had erosion problems on the sides, almost no matter what he did.  He tried to cement the walls, he tried to make rock edges, and inevitably the water cut in behind the man-made materials.  

A beaver would have your situation fixed overnight, they are that good!   Takes a little maintenance each year to make sure it's holding.  Ponds don't just sit there and look great.  They are the weak link in a water system because so much is going on in them.

I have about an acre pond, and the whole month of October is dedicated to Pond Maintenance, when the water is lowest.  But I love the pond, and I'll do whatever it takes to keep it.

You could learn a lot from any local farmers who have built their own ponds.  In my area there are specific plants that are generally used to help with erosion, berm stabilization.  Willows is one of them, and reeds.  There are many different types of willows and reeds, and the best ones for your pond would be what is used locally, native plants.  Reeds need maintenance or they will fill in the whole edge, but there are advantages.  The birds and ducks will bring pond plants in on their feet, so you'll be finding all kinds of stuff you didn't put there that might or might not be a good thing.

I had a somewhat similar problem when bought my property 20 years ago.  There wasa big 10 foot wide and deep erosion hole at the end of the spillway to my pond, with the additional problem that when they subdivided the  property, the end of the spillway was on the neighboring property that I didn't have access to.  I planted a row of a deep rooted running bamboo (Semiarundinaria fastuosa) along the property line where the spillway left my property. The dense rhizome network  that this bamboo has formed has stabilized the soil and stopped the progression of the erosion.   I also planted a 10 foot high running bamboo on my earthen dam that has since spread to totally cover the dam, covering the dam with a 2 foot deep dense rhizome network.  This network has stabilized the dam, keeps tree seedlings from establishing themselves on the dam, and makes it difficult for muskrats to dig holes in the dam.  The bamboo is small enough that I can easily clear cut it from parts of the dam if I ever needed to to maintainance on in.  Unlike tree roots, bamboo rhizomes don't get thicker with age, remaining at their 1 inch thickness for their entire 15 year lifespan and are continually being replaced with new rhizomes to form an impenetrable mesh of rhizomes in the topsoil.  The one time a freak rainstorm dumped 14"of water on my property in a couple of hours, the resulting flood overwhelmed my spillway and overtopped the dam.  The myriad of bamboo stems on the dam caught and trapped debris being carried down by the floodwaters, and actually increased the mass of the dam.  This flood washed out the next dam below mine that was covered with grass.

The other good thing about berm/hillside stabilization plants is that they create a great environment for pond life, insects, birds, frogs, newts, fish, and animals that come to the water to drink.  My pond is spring fed, so it ought to be a giant mosquito mess, but it isn't.  I've never gotten a mosquito bite being on it or near it, because it's so teeming with life that keeps everything in balance.  I wouldn't have believed it if I hadn't seen it first hand.  

There are so many birds nesting in the reeds.   Water bugs, fish and newts eat mosquito larvae.  All sorts of birds nest in the willows.  It's a world unto itself that never ceases to amaze me.  

We have one kind of willow that grows to about 75 feet and then falls over.  Didn't realize it would do this, so now they get chopped off with a pole saw at about 15 feet.  You can also make bent wood furniture from willows, in several colors.  Pussy willow fluff can be used as a down substitute for insulation in garments.  The Indians ate lots of parts of reeds, including the roots.  

The dragonflies also use the reeds to live in, because they need to transform into flying dragonflies.  The other evening I saw some termites out flying around, and a dragonfly flew right up to one and snatched it right out of the air and ate it!!  

Mike, sounds like a great idea with the bamboo.