It will be a lot, as you face several issues.

First issue: This is a very large pond you are looking at, in the range of 11,000 gallons (using the calculations you provided). It sounds as if someone had a very serious koi pond at one time. Although you state you are leaning toward not keeping fish, I would want bottom drains installed in a pond of this size, or you will end up with a mucky mess in a couple of years. If this was a properly designed koi pond, some of that plumbing may still be in place. So the first consideration is that you will need a pump that will filter something on the order of 5,500 to 10,000 gallons per hour, 24 hours a day. A Dolphin Ampmaster ES5500 external pump would perform this function relatively inexpensively, at about 286 watts per hour. I've seen that pump listed for around $400.

The second issue is that a pump like the Dolphin will not push water to the heights you are considering for your waterfall. You need a pump that will push 40 feet or greater "well head" height -- the vertical distance that a pump will raise a column of water. For this, you will need a powerful unit like a Sequence Primer which draws around 1500 watts per hour. That is about the same as a large window air conditioner. Where I live in Virginia, the math works out like this: 1500 watts = 1.5 kWh x 7 cents = $1.05 per hour. (I think the national average cost is more like 10 cents per kWh.)

Therefore, since you must run filtration 24 hours a day, you are probably looking at two pump systems. The filtration could be accomplished with a low-cost unit like the Dolphin. Your waterfall would be fed by a second very powerful pump that you'd run only for those hours each day when you want to operate the waterfall.

You could reduce your cost somewhat by lowering the height of the waterfall. If you are serious about this project, I would recommend first reading up on koi pond design and construction. (There are several websites which specialize in this subject.) Also, some of the experts around here will hopefully chime in. This is not a "garden-variety" pond project that you are considering!

Hi
Curious as to what the "pond" is lined with?? If it has set empty for a long time you'd probably want to reline or at least refurbish.Nothing worse than a leaky liner .Any equipment still intact?? You're talking serious expense for starup, with a pond that size you'll certainly want to do it right. You do have the advantage that the hole is already in place.
camperman gave you some good ideas ,check them out and come up with some kind of budget it will be expensive both to start up and operate. gary

lsst: can you explain why you're running both an external pump and a submersible pump? Do you have a waterfall somewhere that you're using the external pump to run water to?

I can't figure out how to post pictures on here or I could post a pic of my backyard. When I mention the waterfall would be 40' away that is the length, not the vertical climb, it is a gradual slope up the 40'.

There is nothing I have to work with except for the hole in the ground, no liner, no abandoned pumps, nothing.

Putting in bottom drains sounds like a lot of work and huge expense. Is there any reason I couldn't periodically pump the water out of the pond to elsewhere on my 1 acre property to empty it instead? The soil on my property is SO porous that it never puddles even in HEAVY, HEAVY rain, never seen anything so porous.

Camperman is right, the vertical height from top of your pond to your proposed waterfall is a critical measure; It matters very little how far horizontal you wish to go. If it's only 5' of height you'll be able to make a nice waterfall and stream for under 200 watts of power. The same flow going up 40' will draw well over 1000 watts.

Bottom drains allow fantastic reductions in pond maintenence, but they aren't an absolute requirement. I wouldn't build a pond without them, and they're MUCH harder to put in later, but if it were a choice between pond without bottom drain and no pond the former beats the latter. A good pond vacuum works pretty well, and will come in handy with flat-bottom ponds even with BD. BD run continuously - they aren't typically used to drain your pond.

This REALLY desirable size hole you describe would be a gorgeous lily pond with a few fish swimming around in it. A few fish turn into many fish, so a second pump running the filtration from the BD would be really nice. The waterfall pump could come from a skimmer. The whole thing would draw around 300-400 watts if your waterfall is not too high and you choose your pumps carefully - moving 6000-8000 gallons per hour. That would be under $1.00 per day for a really nice pond and waterfall IMHO.

I bought the Tsurumi sub to go with my Pondsweep skimmer before I did a lot of research on ponds.
If I could do it all over again I would go with all external pumps. I have two waterfalls.
I have a third system plumbed in order to add a third filtration system and I will use an external pump there.
The bottom drains are used for keeping the bottom of the pond cleaner and they really help with circulation.

First off the pond will end up being 5500 to 6600 gallons. Yes if you take the length x width x depth x 7.48 gallon per cu ft you come up with 11,200 gallons. But no one has a pond that is a perfect rectangle with perfectly vertical walls. Knowing this I would use either 50 to 60% of the max water that a pond can hold without rock on the bottom and 40 to 50% for ponds with rock on the bottom.

Do you need to run a pump 24 hours a day? With a very low fish population you can get away without running a pump 24 hours a day. Where you may have a problem is the length of the waterfall. You didn't say how wide this waterfall stream will be. But unless you have an extremely wide waterfall stream you won't have a problem. What I am talking about is that so much water is removed from the pond to fill the waterfall/stream that the pond level goes down too much when running and overflows the pond when shut off. In this case unless you are getting close to 15 ft wide for this waterfall/stream with 36,000 to 54,000 gph flow you will not have a problem.

Yes without a pump running 24 hours per day you may have to empty and clean the debris out of the pond once a year. With enough floating plants or a good floating island you won't have a water quality issue.

Do you have a problem with mosquitoes? If so you are going to want some kind of fish to eat the larva.

Gradual slope can mean almost anything from a 6" raise to 10 ft raise. A better estimate of the raise will make it easier to give a better idea of the pump to be used.
Mike

Mike: good points. The pond is egg-shaped and I took measurements at extreme lengths of each and you're correct that sides angle down into the pond.

I haven't designed the waterfall at the top so options are open on that but I would guess the vertical difference from the top of the pond to what will be the top of the waterfall is about 10'.

We don't have a significant mosquito problem here. I'd be open to some inexpensive fish like goldfish but don't have the time or money to get into koi fish... I'm more about filling the giant crater in my backyard! :-)

Perhaps what I should explore doing as a first step is line the pond, put rocks in it/around it and put in a pump/filter to keep water moving, perhaps with a VERY small waterfall at one end of the pond edge that the pump would pump water to and it would flow back in stimulating water movement. Then down the road there is nothing stopping me from adding the waterfall and stream from above? If I were to go this route with just doing the pond as step one would I go with a submersible pump or an external one?

bump!

Sorry I didn't want to stop someone else from posting. Your idea of finishing the hole off and building the waterfall later is a good one. Weather you put a bottom drain in or not that is up to you. You have heard all the advantages and disadvantages so the choice is yours. I would suggest that at least a skimmer be installed but that can be installed later. Now as far as a pump goes I would want to get the pump or pumps that I was going to use when the project was done as a good pump is going to last a while. Since electrical cost are a concern than the only choice is what external pump(s) it will be. This will be determined by the width of the waterfall and finial height of the falls. The only unanswered question is the size of the piping going to the waterfall. And that is determined by how much flow you want over the the falls.
Mike