Slope for waterfall

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Ok, I'm not expecting to get much help with this but I thought maybe their might be an water hydraulics person out here.

I'm working on the waterfall weir for my new pond. The waterfall opening is abotu 21" inches across. The distance between the upper pond and the lower pond that the waterfall traverses is 12". On this 12" ledge I am going to place a piece of flagstone and extend it out past the wall about 1-2". The water will flow over the flagstone and than of course fall into the lower pond.

It was suggested to me that rather than just laying the flagstone down flat, I should slope the flagstone a bit. This will help the water to flow down the flagstone faster and kind of shoot off the edge of the flagstone rather than just flow off. It should help prevent water from wrapping around under the bottom of the flagstone and dribbling down the front of the wall.

The pic below is NOT my pond but a picture of the type of waterfall and issue I'm talking about. You can see how wet the block area is behind and to the sides of the waterfall. While some of this is from splashing, a lot of it is from dripping off the weir.

I think if I have 1/4" drop across the 12" of flagstone that should be enough. Too much of a drop and I think the flagstone/waterfall will look weird.

Craig
 

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addy1

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My piece of flagstone has a 3/4 inch drop, with less the water wrapped under the rock and flowed back. The flagstone has a sharp edge, not rounded which also helps. It is about 18 inches wide, 2 feet long, the water drop is 5 feet to the lower pond. I kept tipping it until the water did not wrap the end of the rock.

DSC02055.jpg


DSC02126.jpg
 

sissy

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That would mean water level would drop a lot and when it is hot out even more water will evaporate from the stones getting hot and absorbing even more water .That could be a big problem and even if you seal the stone you still would have to contend with evaporation .You could maybe bring the stone out farther and go for a sheer desent water fall .Like they do with those plexi glass ones you see a lot of now .I know that fish place online sells a lot of those plastic ones .
 
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So that's a 3/4" drop across 24" wide. That's about 3/8" drop per 12" or roughly a 3.1% incline.

I'm currently at 1/4" per 12" or roughly a 2% incline.

Sounds like I should increase the slope a bit more and go up at least another 1/8 inch before doing my test run. Thanks!!!

My flagstone has a sharp front edge too, along with a slight "V" to the weir. I.e. the exit of the waterfall is slightly narrower than the upper pond entrance to the weir. That should help to slightly increase the velocity as well.

Craig

PS> BTW: I really like your design with the more formal deck pond dropping off into space down into the lower natural pond. Very cool!
 
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That would mean water level would drop a lot and when it is hot out even more water will evaporate from the stones getting hot and absorbing even more water .That could be a big problem and even if you seal the stone you still would have to contend with evaporation .You could maybe bring the stone out farther and go for a sheer desent water fall .Like they do with those plexi glass ones you see a lot of now .I know that fish place online sells a lot of those plastic ones .

Yes. I'm going for the sheer descent off the flagstone with little to no water wrapping around and down the brick wall. I built my own plexiglass weir for my other pond. It's been doing well for the past 16-17 yrs.

The waterfall wall is actually built on part of the lower pond liner so if water ever did find it's way leaking into or on the wall it will all flow back into the pond. But evaporation would still be an issue.

I'm trying to go all natural on this one. So by increasing the velocity of the water through the weir by a combination of the slope and a narrowing of the weir I hope to shoot the water off the edge of the flagstone with little wrap aound and dripping of water.

You are right, a lot of splashing onto, or dribbling down the wall will significantly increase evaporation, especially in summer months when the block heats up. i'm trying to get a nice smooth water entry into the pond with minimal splashing.

Craig
 

addy1

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So that's a 3/4" drop across 24" wide. That's about 3/8" drop per 12" or roughly a 3.1% incline.

I'm currently at 1/4" per 12" or roughly a 2% incline.

Sounds like I should increase the slope a bit more and go up at least another 1/8 inch before doing my test run. Thanks!!!

My flagstone has a sharp front edge too, along with a slight "V" to the weir. I.e. the exit of the waterfall is slightly narrower than the upper pond entrance to the weir. That should help to slightly increase the velocity as well.

Craig

PS> BTW: I really like your design with the more formal deck pond dropping off into space down into the lower natural pond. Very cool!

The deck pond was my honey's suggestion, it turned out nice in our humble opinion, not real deep, the fish do great in the summer, but need to be pulled for the winter, the big ponds water keeps the deck pond healthy.

I measured it for you, the rock is 24 inches wide and 36 inches deep with a 3/4 drop. I just kept tipping the rock until I had the sheer flow then anchored it down at that tilt.
 

taherrmann4

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I didn't use flagstone but mine is probably closer to an inch or two slope. You can see my pics in my signature.
 

sissy

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I know heat and wind effects my pond level ,wind here can blow the water sideways coming off my water fall .I can tell by how wet the one side of the pond gets and sometimes my little house there is soaking wet


 
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I didn't use flagstone but mine is probably closer to an inch or two slope. You can see my pics in my signature.

Nice ponds..
The important value though is the slope. The amount of drop doesn't mean much unless you also know the distance the drop occurs across. An inch or two of difference between the front of the weir and the exit is a big difference. One inch across 24" is an 4% slope, 2" across 24" is a 8% slope. Big difference. To get the same slope across my 12" space I'd need a 1/2" drop for 4% and a 1" drop for 8%. That's a pretty sizable difference in a small span and would be easily seen by the naked eye. I'm trying to avoid an obvious downward angle on the flagstone.

Addy's slope now that she measured it is actually 36" with a 3/4 slope or basically 1/4" per 12" which is a 2% slope. On her first posting when she said 24" deep, that would be a 3% slope. I was originally planning a 2% slope but increased it to 3% based on Addy's first post. Having more of a slope isn't a major problem as long as the weir doesn't wind up looking like a playground slide! i think 2.5 -3% slope is about the limit. Much over a 3% slope and the weir begins to look odd. IMHO At least in a formal pond. A natural pond can probably get away with a steeper slope but usually you're not really building a weir for a natural waterfall.

Thanks for taking the measurement Addy!!

Craig
 

addy1

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NP Craig, After I saw how you were figuring out your slope I decided I had better measure rather than "remember!" lol
 

brandonsdad02

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So I'm interested in the whole plexiglass thing. Do you place the plexiglass under the rock for support, or so the water runs off that instead of the rock? Do you glue your waterfall rock after you tilt it and do you tilt it away from the waterfall so it has more of a drop? I'm rebuilding my waterfall since I took out my skippy filter which fed my falls. And how thick of plexiglass do you use? I want the sheer waterfall but have been stumped on how to pull it off
 
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In my case I just glued, using lots of clear silicone, the plastic directly to the rubber liner. I built the plexiglass weir first, basically two sides and a bottom. Then I just set in on the liner and siliconed it in place. I extended the bottom piece about an inch past the wall of the upper pond. (remember, this is a formal pond).

I have some actual pics of it posted here on the site. I'll find the link for you.

On the new pond, I'm doing something similar but using flagstone for the bottom of the weir and pieces of cut retaining wall stone for the sides.

Craig
 

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