What size do I make my weir?

[Haze7]

I'm building a waterfall out of oolite rock from South Florida that has been smooth cut into 3" slabs that I stacked flat on top of each other to a height of 4.5'. The spillway stone is the same matching stone that I positioned pushed forward 9". The slabs are 5.6" long by 28" wide x 3" thick. 18 slabs stacked on top of each other to a height of 4.5'.

I installed 2 pipes coming up from the base to the top, spaced evenly the width of the structure.
I would like to build a weir at the top behind the spillway. Because of the weight of each stone I was afraid to push it out to far over the pond. They weigh about 250-300 lbs each. Do since I only pushed it out 9", I only have 9" x 66" for a weir. It is 6" deep on the sides and rear. It would spill 3" down onto the spillway stone.

How should I bring in the piping from the 2 pipes? I fabricated a pvc spillway out of 2" pvc (all pipes are 2") Since I have 2 pipes coming up, both with ball valves, I used 2 Ts and connected pieces of pipe to make it 5' wide with ends capped. Then we cut a 1/4" size slit the length of the spillway.

So I guess I have 2 questions.

First, is 9" (but really 7" because the spillway pipe will be in the weir) by 66" by 6" deep flowing up to3" be a big enough weir? Pump size is 12,500 gph.

Second, should I get rid of the pvc spillway and just pipe in with an elbow? It would give the weir 2" more without the pvc spillway being inside the weir.

 

[Haze7]

Sorry the slabs are 5.6' long, not 5.6".

 

[j.w]

@Haze7
I'll let an expert give you advice on this one!
Very beautiful pond and property!

 

[Mmathis]

Hello and welcome!

 

[Jhn]

A better pic or drawing of your plans would be helpful, a close up shot of the waterfalls and basin that feeds it. @combatwombat or @GBBUDD may be able to tell you the amount of flow per inch of spillway you can expect, but I can’t remember the formula and don’t want to look it up at the moment.

IME, a 12,500 gph pump isn’t as much as you think it is, a 5 1/2‘ spill way isn’t going to be a raging waterfall. I have a 12,000 gph pump (but really less due to head loss, turns in the pipe, distance from pump to spillway, etc.) pumping into a 3’ wide spillway, doesn’t even come close to 6” deep.

if you are talkin about that stepped spill way on the right of your pic, if you don’t have that inside the liner, you may get some splash out as the water rolls down it, but shouldn’t spill over the sides of it. If by chance it does, put a tee or Y in the feed line with a gate valve and divert some flow back into the pond elsewhere until you get it dialed in.

 

[Haze7]

The pond liner is under the waterfall too. I built up the the area in the pond in front of the waterfall to give it more strength. There is a 6" concrete slab under the waterfall. The total weight of the waterfall is about 5000 lbs.

I wanted to mimimize any settling from the weight so I put 2 staggered rows of concrete block filled with soil and sand under the liner in front of the waterfall. I put the flat stones on top to hide the liner but the water is hitting them and I'm still trying to figure that out too.

I agree the 12,500 gph pump I have is affected by the same things you mentioned. 4.5' lift, distance from the pump and 1 angled turn in the pipe.

Thanks for your response. Sounds like my weir size may be ok based on your reply.

Here is a picture of the pvc weir I put together. I'm calling the pvc a weir because I don't know what to call it. The real weir area is behind it. I had originally put the pvc in the weir area but a friend of mine who builds incredible waterfalls said to just put it on top of the spillway stone like in the picture. I don't really like the water flow this way, hence me coming here to inquire about using the narrow weir that is currently behind the pvc. I can shift the pvc back or remove the entire thing and just have 2 elbows into the weir area from the 2 vertical pipes coming up the back of the waterfall. I did secure and seal the weir area with mortar after this picture was taken. I'll have to disassemble and rebuild.

 

[Haze7]

I have a ball valve on each vertical pipe that supply the water to the waterfall.

 

[Haze7]

Hm. The weir isn't 9" - I have the border stones in the back. So 6" wide.

 

[Haze7]

Here are some more pictures.