I am in the process of reclaiming my second pond which was drained by trenching through the dam. It is 2.5-3 acres in size and the dam is about 80 yards long. The pre-existing water level was only about 2-3 feet below the top of the dam so when a big rain came water could run over the dam. Approximately 700 acres drain through this pond. I totally understand and agree with coring. I want to raise my dam approximately 3 feet so that there will be less of a chance of water running over the dam. (I have replaced about 700 yards of dirt below the dam that had washed away)

My question is does anyone have any input on the size of the core in the dam so that I could add height to it? I was thinking 3-4 feet wide and 4-5 feet deep? I am planning on removing all the grass off the dam during the process as well.

I am slightly confused (about this; very confused about many other things). Is there an existing core in the dam, or are you going to rework the dam to add a core as well as increase the height?

Sounds to me like a "core" on top of the existing dam. Build up the height from there...I believe he just wants to raise the dam height, and this would help bond the two layers together.

Workable?

We had some posts lost here.

For reference, IIRC cwooten isn't sure if the existing dam has a core or not.

I think the best advice is to dig down into the existing dam a little, and if there is an existing core, to tie it into the add-on core as described in Lusk's "Perfect Pond: Want One?" book. They have to be tied together both for water-resistance (no leaking) and mechanical keying (no sloughing off) reasons.

If there is no existing core, I would want to retrofit one. That's a big job. I know a pond where it was done, but it had really serious leakage problems which needed (and were) alleviated.

Matt said it better than I did. The existing dam did fine. I will just core it and raise it. Anyone done that? I know I am not the first.

I wouldn't waist my money if you can't increase your spillway width along with raising the dam or you are going to have to raise the dam considerabley and then you get into safety issues. 700 acres of water is a lot to deal with especially in your neck of the woods.

Craig, I don't think I've ever heard of properly coring an existing dam without taking a big chunk out of the middle from end to end. Is that what you're planning or am I missing something (I often do).

i think RT nailed a potenttial problem, if the dam was overtopped during max watershed flow before, and if you dont increase the width of spillway, and if you raise dam, all you do is trap more water that will eventually overtop the dam. from yer watershed area, you need to calculate and modify spillway width to handle flow from the largest possible storm event...maybe you know this already and just didnt mention it?

Yes, I am planning on coring the existing dam from end to end. It is only about 80-100 yards long. It looks like I am going to have to extend the spillway length as suggested by RT. I have not calculated the needed size of the spillway. Where do I get that info. Any more input on the size of the core?

We did lose some posts for cwooten on this thread, but the stuff I was referring to comes from Publication 590 . This would include some coring fundamentals and alot of water flow calculations. (be sure to afix your brain bucket to keep your head from exploding; the calculations can appear to be overwhelming, but make sense if you go at it in an orderly manner)