Garden pond

I hope someone can help me. I'm constructing a garden pond. Two actually, with a waterfall between them. The first pond is 8'' deep 30'' long, 36'' wide narrowing down to 17'' wide. At this point it narrows to a 12'' wide channel 8'' deep and 40'' long. Over that 40'' the channel widens to 19'' and ends at a waterfall created by a 19'' wide sandstone block. the water level in the pond will be approximately 1 inch higher than the top of the block allowing water to flow over. The second pond, which is to be lower than the first pond, has not been constructed yet. So the idea is, when the pump stops, the first pond level over the whole area of water will drop by only an inch. That's the theory.
Could you advise what type of pump I need and filter and does the second pond need to have the same volume of water as the first pond. And any other recommendations that would help. Sorry for the lengthy query and I hope you haven't lost the will to live Many thanks. P,S, sorry forgot to mention there will be no fish or plants in the pond. However, there are plants around the pond and lots of small birds, crows and magpies.

Liamondo said:

does the second pond need to have the same volume of water as the first pond.

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no?

Doing a few quick average calculations based on the dimensions supplied the upper pond will contain about 50 gallons of water, and to get a waterfall flowing across a 19" gap will need a minimum flow rate of 1000GPH - ignoring any height difference between ponds or pipework restrictions. The bottom pond will need to be big enough to cope with the amount of water being pumped out of it to provide the waterfall and also to accommodate the water which will flow from the top pond when the pump is not running. The level will drop in the bottom pond significantly when the pump is running if it is a small volume. As you are not having fish in the pond the filter fill not need to process any fish waste - but you may want to have a filter / system designed to keep the water clear - to avoid it going green - as there are no plants going in the pond then the whole of the surface area will be exposed to light / sun and will go green with algae quite quickly.

hanks mbaines1, for your time and feedback. Sorry didn't reply earlier, been away for a few days. One question, once the upper pond water level drops by approx. 1 to 1.5 inches, when the pump is not running, no more water will flow into the lower pond. It'll be trapped behind the waterfall stone block. Is this volume of what you are referring to when you say, Thanks again

also to accommodate the water which will flow from the top pond when the pump is not running.

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Yes - in effect the bottom pond needs to be big enough to allow water to be pumped from it, fill all the pipework plus any filter and increase the upper pond level by an amount to allow it to then overflow - you will only increase the upper pond depth by 1/4" - 1/2" I would guess unless you use a much bigger pump. A 1/4"-1/2" deep flow of water though will look quite effective on a waterfall.

If the bottom pond has a small capacity though the water level will drop significantly when the pumps running which will look wrong, as whatever material the bottom pond is made from will then be visible and if a liner will be subject to damage from the sun. The larger capacity the lower pond - the smaller the drop in level when the pump is running.

Once you have your upper pond complete, you could see how much water / hour is needed by initially using the garden hose - time how long it takes to fill a known capacity (bucket or similar) work out how many gallons / hour it runs at, then fill upper pond and let it overflow - you will see what that amount of water / hour looks like then scale up the flow rate as needed. Here our tap does about 200 gallons per hour so about 1/5 of the amount your likely to need to get an effective 19" wide waterfall.

Remember the length of pipe from pump to upper pond, the diameter of the pipe, the difference in height between water levels in upper and lower pond, the type of filter will all have an impact on the flow rate of the pump.

Many thanks again for the time you have taken to respond. You've really helped.