I just purchased a property with an old washed out pond. I need advise on repair.

I need to repair a wash out in the wall. I would like to do it with cement because I believe I can rock it and make it more aesthetically pleasing. If I dig down and place a cement key way, can the water still leak under it. How do I tie the cement into the existing dirt walls?

From what I can gather, this pond is close to 100 years old. It is placed at the head of a seasonal ravine/creek so it's "walls" are ground level most of the way around. Where the elevation declines on the western side an earth dam was erected to create the pond. It is currently only holding water about 1' deep at a diameter of maybe15'. The washed out segment of the dam wall is only 2' across and the height from water level to the top of the old wall is 4'. Judging by what I can see of the old water lines, at the original fill level, the pond was around 60' in diameter, 6' deep.

I don't think you can do that. I see no way to get the soil to adhere to the cement.

Welcome to Pond Boss! You're in the right spot for help. Sit tight and wait for some experts to chime in, but take solace in knowing you are within range of the one of the best pond builders around - Mike Otto. Mike is on the forum as are many other experienced builders, so hang on and see what they have to say.

Post some pictures if you can. That always helps us envision what you have going on and, more importantly, we're just suckers for pictures!

Maybe you could do a conventional soil repair and add a rock cement face for looks.

Ditto what Dave said (and Todd). Clay would be cheaper and easier to repair if something happened down the road. If the concrete cracked and water started leaking through it, how would you patch it? Not to add getting the soil to adhere to the concrete and make a waterproof barrier.

I'd dig some test holes in the dam and see if it had a proper "key". If not, now's the time to repair the whole thing correctly, not put a bandaid on it.

Hi
Congrats, sounds like a great location!
I'll triple up on others comments, it's a dirt walled dam, you repair it with dirt, close to whats there - Big name civil engineers mess up hybrid dams, not something for us small fry to play with.
100 yrs as a dirt dam, why mess with sucess, patch it up to match and you'll get another 100 yrs.

Facing with rock laid in concrete (it's concrete, not cement, you'll get more cred calling it concrete, cement is part of what's in concrete) might be nice, unless it freezes. Rocks on sand on a liner might last longer.
For more on the above, see below where I go on and on and....

If it freezes in this area, might want to think again though. Even just a couple of days at freezing can cause expansion / contraction cracking, water gets in, freezes, crack gets bigger, 5 yrs down the line you have loose rock with concrete stuck to it. Deeper freezing can heave ground under and accelerate the process. As it seems you pond is mostly exposed in dry weather, probably going into cold season is a pretty dry time, the rock and concrete facing seems likely to be fully exposed.
Might want to remove a bit of dirt at sides and bottom of hole, get rid of any organics that worked their way in, seeds even, have fill similar to what the dam is made of hauled in, WITH NO ORGANIC MATERIAL in it, tamp in 6 inch layer, that is, rake out 6 inches deep, tamp, dump in more material, rake, tamp, rent a vibrating tamper, you can run a truck over it, but will need to tamp edges against old soil, and the old soil adjacent the hole. If the soil fill is stone dry, dampen it, just a bit, NO MUD. rake and tamp in layers.
You might want to consider a full or partial height pond liner. Seems you are dependent on rain, and it mostly dries up, a liner will keep water in longer. Oddly, you might think, you might want to cover all or part with sand and some soil from the bottom, to recreate the bio system that's been keeping the pond clean and useful.
Having said that, this pond is no doubt recharging a local aquifer / bio system, and adding a liner might impact adjacent plantings, up to a few hundred feet away. Really tough to say if it is. If you do line it, at the discharge, create a recharge basin / bed that will let overflow in the wet seasons fully sink in and recharge the local bio system.
Good luck!
Roughdesigns