I have rain about 8 months out of the year and dry for the remainder. During the rain Ifill up in the second month and the rest goes over the spillway.

What I would like to do is pump water from the bottom of the pond to replace the overflow caused by the rain. The pond is about 12 to 15 feet deep. I want to place the pickup near the bottom and use the water level to turn on and off the pump, sorta like a toilet tank float switch.
I don't intend for the pump to keep up with rain fall just keep close to the underground transfer. That runs about half to 3/4s of and inch a day.
It's my idea so I don't see any flaws and that means that I need help.

Dang, Rad...you been hangin' out here since September 16 without a single bump. I didn't even know you were here (not surprising since I hang close to the comfort of the pond building forums).
So, the first thing that comes to my mind is the ejector pumps that are used for downstairs bathrooms. If it were installed inside a cage like a live box, it would act as a pre-filter (you know, the 2 or 3 ft rectangular boxes made of galvanized mesh that get tied to the side of the pier). You might attach a couple PVC pipes as vertical handles to lower it the bottom. I fear, tho, that those motors may not be designed for continuous use; not sure. The impeller design is perfect, capable of moving chunks up to 1.5 - 2", so there would be no possibility of a log-jam.
If you google ejector pump , you're gonna find alot of info, including some killer commercial grade units. Matching killer price, too, I imagine.

Thanks Bretski,
I was thinking of a simple system, 1" pvc pickup in a cage to keep it off of the bottom and clear of debris with the pump on land in a small enclosure. I want to use a float switch. I think the pump would run 24/7 for about 6 or 7 months a year. I know I can't draw down the same amount of water I receive in rain, just hoping to get some from the bottom out.
Has anybody done this, or similar, and if so is it of any use?

I don't see anything wrong with your thinking Rad. It's done all the time in garden ponds. My oldest son built one. He purchased a submersible pump from Lowes for apx. $130.00.
I would consider putting a tee & a couple of valves on the discharge & an additional pipe back to the intake which would allow you to blow any build-up on the cage off.
Another thought, could there be any use for the water removed? Maybe just for aesthetics such as a man made stream, waterfall or waterwheel?

Radd I am posting so you will come back on the top of the list.

Rad we use a plain siphon to take water off the bottom and over the dam. Not sure this helps any but it is easy and cheap.

ewest,
I first thought of a siphon, but I want to remove the water at about 12-15' and I can't get nearly that low on the outside. And if I remember correctly, when we used to borrow gas, late at night in south Texas, the out had to be lower than the in.
Ric
The place where the water will exit is over the existing spillway, which is sort of a waterfall now, just not visible unless you are on top of it. But, I have another question, both you and Bretski mentioned a submersible pump and I was considering a non submersible. Is there an advantage with either?

Rad, one of the considerations is the lifting ability and efficiency of pumps. All things considered equal (hp, size) a pump can push water much higher than it can lift. I know people who have extremely deep, 400 to 500 ft., water wells. It would take a huge pump to lift water that high. However, being submersed, it can very efficiently push it to the surface and have a long life.

Gee, this pond stuff is so simple, all you have to do is ask. I'll check pump specs this week.
Thanks Dave