Fish Screen

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I am a newbie and in the design phase of a two tiered waterfall/pond system. I have two basic questions right now. First, my waterfall and upper pond will be the most prominent feature to the viewer. I would like the upper pond (8 feet diameter x 2 feet deep) to be larger than the lower (6 foot diameter) pond. there will be a stream about 45 feet long dropping about 6 feet in elevation from the upper to lower pond. I plan on running the pump 24x7, but there will be times I will want to shut it down for maintenance and such. How to I keep the water in the stream from flooding and overflowing the lower pond when the pump is shut off? Can I retain the water in the stream without it being wasted and overflowing the the lower pond? And is there any issue I am overlooking by having a larger pond at the top?
My second main question is about screening fish. I would like some gold fish only in the upper pond since it is most prominent. Is there a way to design a screen in the outflow of the upper pond to keep fish from being washed down steam and into the pond below? My thought is to use rabbit cage mesh screen and cut it the shape of the stream contour and attach it to a log sitting across the stream channel. Does this sound about right? See the attached cross section sketch for a visual.
 

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Mmathis

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Hello and welcome!

I've always thought that the lower or catch pond was supposed to be larger volume than the top...... Is there a reason that you can't reverse that? Or perhaps you could make the lower pond deeper so that it could hold more water, but keep the L & W dimensions the same? I think it has to do with physics.

I personally don't like the idea of screening the fish. It seems that the screen material could harm the fish, especially if they were to get caught in it. There are others on here with tiered ponds, so maybe they can offer advice on ways to keep fish in just the top pond. For the most part, I think the fish will stay, but you're always going to get escapees, especially when they reproduce and there are fry.

And another problem with putting up a screen or other physical barrier is that there will be debris that gets caught in the screen, and unless you are super diligent about cleaning it, eventually you're going to end up with a dam -- which means your top pond will overflow until you have no water left in either pond.
 

addy1

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Welcome to our forum!

You could have a lot of catch basins in the stream. Some of the stream water would stay in the stream.

A screen will only stop the adult goldfish. They lay eggs, then it is fry, those tiny little fish / eggs will just flow right down the stream and populate the lower pond. I have some gf in my fishless no longer small ponds. Those fry/eggs even went through the pump down a long garden hose to water fall into those ponds. I found 3-4 fish in ponds I did not put fish in.

My large pond, when the stream is running, loses around a inch in water depth, then regains it once the stream is off. My stream is around 85 feet long with catch basins.
 

DeepWater

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A 45 foot long stream, with a 6 foot drop, will hold a LOT of water when it is running. If you shut off the pump, water will flow from the upper pond to the lower pond in 3 or 4 methods:

1. all the water in the pump lines will drain back to the lower pond.
2. the upper pond will drain to the lowest lip of the outflow stream
3. all of the moving water in the stream will drain to the lower pond.
4. *syphon* action - depending on piping, the upper pond can drain back to the lower pond through a syphon action until it gets low enough that air enters the pipe.

Given this volume of water, can the lower pond absorb it all without dumping it out an overflow? That way when the pump is turned back on, all that water can go back to the system. Depending on surface area of lower pond, and volume of stream water, the lower pond will rise what, 1", 2", 6"?

I agree a screen is a bad idea, essentially because it's a debris screen that will clog up and then could cause an overflow, draining of water, and even potentially pump burn-out...
 
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Thanks all for the response. I maybe should have clarified that I would not mind having fish in the lower pond, it is just that the upper pond will be the featured attraction due to it's proximity to the house and deck. And I could make the lower pond as big or bigger than the upper, but I'm trying to limit unneeded excavation effort and liner costs.
 
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A 45 foot long stream, with a 6 foot drop, will hold a LOT of water when it is running. If you shut off the pump, water will flow from the upper pond to the lower pond in 3 or 4 methods:

1. all the water in the pump lines will drain back to the lower pond.
2. the upper pond will drain to the lowest lip of the outflow stream
3. all of the moving water in the stream will drain to the lower pond.
4. *syphon* action - depending on piping, the upper pond can drain back to the lower pond through a syphon action until it gets low enough that air enters the pipe.

Given this volume of water, can the lower pond absorb it all without dumping it out an overflow? That way when the pump is turned back on, all that water can go back to the system. Depending on surface area of lower pond, and volume of stream water, the lower pond will rise what, 1", 2", 6"?

I agree a screen is a bad idea, essentially because it's a debris screen that will clog up and then could cause an overflow, draining of water, and even potentially pump burn-out...
I had not thought about the siphon effect, but the outflow of the pump will be plumbed to the top of the waterfall so I should not need to worry about siphoning, correct?
 

addy1

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I had not thought about the siphon effect, but the outflow of the pump will be plumbed to the top of the waterfall so I should not need to worry about siphoning, correct?
As long as the outflow line will suck air instead of water when the pump stops running.
 
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