Any idea what it is going to take and cost to fix th
is problem?

Unopened bags of cement and poking a few holes in them

is this where water was supposed to flow out and it just cut it out? If so a fair amount, if that's not the primary overflow fill it back in with dirt and get grass growing, or top it with rock or crete like beaver said

Call NRCS or your county agent. There are several programs available for erosion control such as the issue you are facing.

Rent a skid steer and rebuild it, and plant with strong root grasses. If you do not have an overflow already in place, build one somewhere on the edge of the dam where the over flow will not cut into the backside of the dam.

Pretty cheap endeavor, ~$200 bucks to rent the skid steer, one or two 8-10" PVC pipes for overflow ~$50

Another option, since your dam is already compromised all the way to the original ground level think about putting in a control structure.

You need to have a good idea why it failed in the first place. If you just build the damn back like it was you are asking for the same thing to happen a 2nd time for the exact same reason. Is the problem with the slope of the dam, location of spillway, size of spillway, type of soil, etc.

how deep is it?

This is where the dam drain was. It was a 36 inch or so metal Culvert about 15' long. We believe it was caused by beavers or otters. The whole is about 8' wide by about 10' deep by about 15' long this pond is about 5 acres or so.

wow 5 acres is a special pond. If you know beavers to be in the area and that they caused a blockage than another 36 inch culvert Imight work again. Having repaired my spillway in early summer after the record spring rains and now again after heavy fall winter rains and run off again today. Best idea for that size pond would be to get the NRCS office to schedule one of the States engineers to come see and advise. They informed me that I was catching run off from some 98 acres. I have no idea if 36 inch is big enough or not. Any work you want to do will need some drying out to re-gain the compaction to avoid being washed out in the future

Luckily it's towards the end of the dam. May make it easier to fix. I am going to contact a local pond builder and talk to him. He built my current duck pond we hunt.

I've got two to repair when it dries out.

Get someone with a dozer its going to have to be packed good

Got a great guy in N Tx PM me. Did all kinds of dam repair, enlarged wetland, installed water control etc

I agree that is how we fix all of ours and then sand bag it from the front and behind it works good

But if you are playing with 10' deep your gonna have to have the NRCS come out and look out it, because 10ft is a lot of dirt

This plus is cheaper then doing it twice.

could the BLM help maybe?

For sure but don't call them before 4:20. They get grumpy

I can understand that, I'm pretty grumpy until about 4:20 myself

I can tell

I'm operating on eastern time today, I'll get back with you in a few

We had the same thing happen on our lease last year. Put in a flashboard riser. Best thing we've ever done on the lease. Farmer had a dozer and we bought the riser. Riser was about $500 I think. Ground was so hard that a tractor bucket couldn't touch the ground though...we lucked out that the dozer was on site when we needed it.

^^^^Great idea but a flash board riser probably wouldn't work that great in 10ft of water that's a huge board and the dirt underneath to make a smaller one is just gonna wash away I'd think