Flow rate for an unusual weir

dustboy

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I would like to construct a weir by basically cutting a slot lengthwise in the side of a large piece of square aluminum tube. The slot would be about 66” long, and maybe 1/8” or 1/4” wide.

How do I figure out the flow rate to achieve a nice even waterfall across the entire length?

I’m finally building my dream pond! Got the hole dug this weekend, about 6’x12’x28” deep. My wife was horrified but as with most things I build, she eventually wonders how we lived without it.
 
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sissy

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I was looking at my metal vent for my microwave outside today while weeding and thought what a great weir that would make .a pic of it would help .It has a spring door inside this that comes off if you want it too
100_5557.JPG
 
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dustboy

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Here is the aluminum beam, it was the gantry beam from a CNC router I owned. It had a manufacturing defect and they replaced it. I couldn't throw away a beautiful chunk of metal like this, so now maybe it will find a purpose.

My plan is to cap the ends and cut a long slot on the vertical side, to create a wide, flat waterfall. Not sure what I will use to support it, maybe a low wall with pavers. It will sit about 18" above the water level.


Here is the whole, uh, hole. Needs a bit of reinforcing at the deep end, which is 28" deep and tapers up to grade level where the bog will be.


I'm hoping for something like this:
 
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sissy

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gosh you are right it would look great .Can't see why it would not work .You may have to decide which pump would work for the best flow .A ball valve on the pump with another hose on it will make it easier to decide on the flow you need and want .But just like wood metal is a pretty thing
 
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I would cut the slot on the bottom edge of the tube and then tilt it slightly so the water will not wick back along the bottom. I know structurally it would be better to cut the slot in the center but I think the water would flow better off the bottom. Try it out with a water hose before you install it to make sure you are happy with it.
 

dustboy

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Good point Ronfire, I have noticed most of the weirs available for sale have a lip to prevent the teapot effect. It might be cool anyway to create a flat curtain of water falling from the bottom of the tube.
 
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It would be worth a try. If the water wants to wick back along the bottom is to glue a small strip along the bottom of the tube that hangs down. Any material that is fish safe will work even just a bead of glue. Better yet is to cut a slight grove along the bottom if the material is thick enough. With aluminum you can even cut it with a skill saw. Definitely would like to see how it works.
 

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I would think you would want the slit for water to come out at the top. If the tube has to fill up with water then pour out the slit, I think you will get a more even flow across the entire slit this way.

I have a pond less water feature. I used a 3/4" pvc pipe and cut a slit along its length for the water to come out at he top of the waterfall. It comes out uneven and more towards the end of the pipe/slit because of the pump pressure.

The good thing about your tube is you could just flip it over to have the slit at the top or bottom depending upon which works better. Like mentioned above, I would test it before officially committing. This will allow you to get the inlet on the correct side (to where your pump tubing is running). Also, I would think the inlet needs to be towards the bottom of the tube. If you install the inlet then end up flipping the tube over, your inlet is going to change.

I wish I could advise you on the correct flow rate, but I don't know.
 

sissy

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get a bvigger pump and a ball valve this way you can adjust the water coming out .This way you are not guessing on the pump
 

dustboy

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I'll still be guessing. If the pond is 1,000 gal then normally I would get a 1,000 GPH pump. But I have no idea if that is even enough to get the waterfall to work right.

The pump should be able to run the waterfall plus move some water through the bog. A 3-way valve could be used to balance the flow between the two.
 
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Another thought would be to cut out the corner of the tube then you already have the lip. It would be great if you had a spare short piece to experiment with.
 

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sissy

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you could use 2 laguna pumps .I have 2400 gph and a 2900 gph and total watts used is just over 100 watts 65 for 1 and 35 for the other ,the bigger the hose the less watts they use
 
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have a lip to prevent the teapot effect
I vote for attaching a shut The flow rate is irrelevant for making the water run across the entire weir. so long as it is level. my guess in the picture you have as an example is pushing at least 6,000 gph a standard pool pump.
it takes a lot of flow to generate a nice wide waterfall
 
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