Question on plumbing from BD to settlement

[mpagri]

Last year i installed a 3" bottom drain on my 2000 gallon (9ftx12ftx2.5ft) pond and plumbed it to a filter pit with two 55g drums in parallel. I made a few crucial engineering errors and want to redo it this year. The issue I am aware of is that I ran only 2" pipe from the drain to the barrels and I have 90 degree angles. I think I should have went with 4" and only 45 degree angles. The other issue that I am unclear on is that i raised the drain piping from the bottom to about 1 foot below the surface of the pond. Will debris be able to make the climb or will it settle inside the pipe? The drums don't start to fill till the pond is over 3/4 full and the flow is very slow. I will be buying a new pump, external?, and will match the GPH as needed, at the moment I do not know what GPH will be.

Thanks

 

[Waterbug]

The issue I am aware of is that I ran only 2" pipe from the drain to the barrels and I have 90 degree angles. I think I should have went with 4" and only 45 degree angles.

Not sure if you mean the entire drain should have been 4" or you should have split the 3" into two 4" going to the barrels. No reason to split 3" to 4" that I can think of. 3" to 3" is fine. You may want 4" coming out of the barrels, but 3" is probably OK. Not sure what's after the barrels.

The 45's vs 90's really depend on the flow rate. For low flow rates the loss may not be that big a deal. Sweeps are also useful, but a little pricey.

The other issue that I am unclear on is that i raised the drain piping from the bottom to about 1 foot below the surface of the pond. Will debris be able to make the climb or will it settle inside the pipe?

The debris thing doesn't have anything to do with climb or whether the pipe is 1' or 1" below the surface. It's a really difficult concept, one of the hardest, but fluid mechanics is really alien to what we're used to. Debris is basically weightless, so it isn't effected by gravity, or effected so little it's hardly worth noting. It's why sloped bottoms aren't needed. Gravity is not relevant.

So it's all about flow. It's the only force that moves debris in a weightless environment. There are no formal rules about how much flow should be pushed thru a BD pipe. The more flow the less chance of settling and clogs. For a 3" pipe a flow of 1500 to 2500 GPH is kind of generally thought to be a minimum. But all the filters the water goes thru also has to be considered.

The drums don't start to fill till the pond is over 3/4 full and the flow is very slow.

I don't know what this means. The barrels will start to fill when the water level in the pond is is higher than the bottom of the barrel inlets.

Unless the pipe goes higher someplace and then back down which isn't good. That will normally cause a vapor lock and problems.

There is also an issue called "draw down". The water in the barrels will always be lower than the water in the pond. The amount of draw down depends on flow rate and some other factors.

I was just in a thread were someone said BD systems don't have to be complicated or something like that. To me they are complicated...unless a person ignores the details and relies on luck and low expectations. This post only hit on a couple of points.

 

[HTH]

The debris thing doesn't have anything to do with climb or whether the pipe is 1' or 1" below the surface. It's a really difficult concept, one of the hardest, but fluid mechanics is really alien to what we're used to. Debris is basically weightless, so it isn't effected by gravity, or effected so little it's hardly worth noting. It's why sloped bottoms aren't needed. Gravity is not relevant.

So it's all about flow. It's the only force that moves debris in a weightless environment. There are no formal rules about how much flow should be pushed thru a BD pipe. The more flow the less chance of settling and clogs. For a 3" pipe a flow of 1500 to 2500 GPH is kind of generally thought to be a minimum. But all the filters the water goes thru also has to be considered.

I think you are saying that with 'proper' flow typical pond debris will not settle. Settling tanks work so, gravity must be a factor, but with enough flow it is has negligible effect.

Then it must follow that if debris do not settle there is no point in having a bottom drain.

 

[Waterbug]

Yes, true.

It's like dust in the air, it will settle if the air is still enough. Dust is effected by gravity. But the amount of flow needed to keep it suspended is very little. 1 GPH moving thru a 3" pipe would move pretty much any pond debris vertically equally as well as it would move the object horizontally..Gravity would be such a small factor it can be safely removed from the equation.

Macroalgae (string algae, etc.) is problematic and probably the reason for 1500 - 2500 GPH flow being considered the minimum. But I'd say this is more of a size thing than gravity. A clump of detached algae will move pretty easy with little flow. But getting a large clump thru a pipe can be a problem. Larger the clump, larger the problem. Leaves would also be in this category. Sticks are a problem as they get stuck in the pipe but no way around that.

I think this is why 4" pipe is the preferred size and 2" is considered way too small.

But nether pipe size or flow can handle all clumps. Even 4" high flow pipes can be clogged. The theory is a person would have fewer clogs the larger the pipe and/or the higher the flow. I'm not sure how true the theory is. Certainly somewhat true. But of course that depends on the macroalgae. To a person going thru a string algae die off and having to clear clogs once a day it probably doesn't matter much that they could have had 10% fewer clogs if only they had used 4" instead of 3" I'm not sure the theory would matter much.

So to me, gravity is not relevant when thinking about pipes being vertical or horizontal or being close to the surface or not. The relevant force is flow.

I disagree with the concept that settlement tanks work, but understand "work" is a relative term. I do think it's safe to say that settlement tank use has been in decline over the best 20 years. 20 years ago settlement tanks were virtually ubiquitous in the design of serious ponds. Today very rare.

 

[HTH]

Yeah that relative term work is the kicker.

I had one that worked 'well' in a good sized unfiltered pond. About half the pond was a bowl or bathroom sink shapped area for the koi. The other half was a stepped affair for goldfish and lilies. There was a water fall connecting the two.

I had the 4" bottom drain capped off one foot below the water level of the koi basin. About once a week I would remove the cap and the water would slowly start moving then gush out the pipe. The crud that came out was amazing. It did a decent job of keeping crap from building up on the bottom but was far from perfect and the water was never clear. Which was not a bad thing with the herons in the area. The koi basin is in the upper half of this picture and lily area is off the image to the left. The formal pond in the foreground eventually got its own filter and greenhouse. I like this picture because the iris are blooming and it is snowing.

What you said about not needing a sloped bottom makes sense for the BD with radial inputs and filter. I am thinking it did help with the system I was using.

I had planned on filtering this pond but work got in the way. When I moved the liners came with me and I plan on giving it another try.

 

[Waterbug]

Yes, good old "works". Also time relative imo. For the first few years many things in a pond "work". As times passes, stuff accumulates, fish get larger, peoples' definition of "works" can change.

The sloped bottom thing is interesting. I've read several compelling posts on why a sloped bottom reduces BD function. All goes back to water current and how more current is forced to the upper levels reducing current at the bottom. Water currents are of course well studied. But it's not really possible to say a sloped vs flat is better or worse in pond applications. It's a variable system. Plus position of water jets, flow amounts and pond wall surface material would all be factors. I have to assume sloped would perform better than flat with some combination of jets, etc. And there's not exactly a lot of good data on pond applications.

To me the sloped vs flat thing is almost always thinking gravity has the same effect on underwater objects as we experience in our world. So in that context I think it's a mistake worth pointing out because people can go to a lot of trouble digging a sloped bottom. Nothing wrong with experimenting with a sloped bottom if there's some theory to test other than gravity.

 

[HTH]

thinking gravity has the same effect on underwater objects as we experience in our world.

Oh fun physics time!

Under water gravity is seen as buoyancy. Things lighter then water float and heavier things sink. We actually have the same thing in air but so few things are lighter that we do not tend to think of it that way. So gravity is still there but there are a much larger group of thing that float.

Many of the particles in water are so close to being buoyant neutral with water that they fall very slowly. That lets current carry them to the filters.

For a flat bottom to work you need to have current at the bottom of the pond to keep the debris moving along. If there is not current you will get dead spots. Slanting the bottom gets rid of these dead areas, but once can put a few jets in near the bottom not need the slant.

Did I get it right ?

 

[mpagri]

If I remember correctly (I'll clean out the pipes and filter pit and experiment with this again during the week) the biggest issue was the drawn down. The barrels were not filling fast enough to compensate for the loss in the barrel by the pump. The flow into the barrel also did not seem fast enough to create a wide enough radius of suction in the pond to pull debris into the drain. What would be the first place to start to troubleshoot this issue?

 

[HTH]

If I remember correctly (I'll clean out the pipes and filter pit and experiment with this again during the week) the biggest issue was the drawn down. The barrels were not filling fast enough to compensate for the loss in the barrel by the pump. The flow into the barrel also did not seem fast enough to create a wide enough radius of suction in the pond to pull debris into the drain. What would be the first place to start to troubleshoot this issue?

If I recall correctly you are gravity feeding the barrels from the bottom drain. Two things come into play. The first is the discharge height of the drain. The lower this is relative to the pond surface the more pressure and flow you will have. The second is pipe size.

Given that lowering you barrels will cause them to overflow I would try 4" pipe first.

 

[Mucky_Waters]

Sloped bottoms and water current work together to move mulm towards a bottom drain. It doesn't take much current because the stuff is so buoyant, but as long as there is a slight current and the bottom of the pond is sloped mulm will continue to work it's way towards the lowest part of the pond or pool If you have a bottom drain there it will eventually get sucked up. Sloped bottoms "work", all I have to do is look inside my cone shaped sediment tank to see where all the heavier muck is accumulating to see that that is true.
Of course it only works with the right kind of stuff, obviously if the stuff is too heavy, like small rocks or sand, the water current in a pond with only a slight slope may not be able to move it, and if it's too buoyant it may not sink in the first place. Also, restrictions on the bottom of the pond (rocks, wrinkles in the liner or thick algae growth) could impede the movement as well, so it all has to work together.

 

[mpagri]

If I recall correctly you are gravity feeding the barrels from the bottom drain. Two things come into play. The first is the discharge height of the drain. The lower this is relative to the pond surface the more pressure and flow you will have. The second is pipe size.

Given that lowering you barrels will cause them to overflow I would try 4" pipe first.

Is the alternative to gravity fed would I have to change to a pressurized system?


Thank you all so much for your help. I am excited to figure this out this season.

I made a crude design that I attached.

I think I should have taken the skimmer direct to the pump and not joint with the BD pipe.

 

[HTH]

I like gravity feed to the filter because you can remove the solids before the water gets to the pump and you never overflow a filter box.. When using a pump to feed the filter you have to keep an input screen or some sort clean. So I favor a gravity feed to the filter. It is a good idea to have a float type shut off for the pump should the filter clog and not flow enough to feed the pump.

I am a little mystified why your system did not work as you set it up even with the 2 inch pipe. How many 90 degree elbows do you have?
Can we get some pictures.

 

[Mucky_Waters]

I'm curious why you reduced the 3" bottom drain to a 2" pipe? Why didn't you just run it 3" all the way to the filter tanks? That's normally how it's done.

 

[mpagri]

At the time I did not think that 2" pipe would be an issue, it seemed much easier to cut and work with plus the availability and expense of all the valves and connectors lead me to choose 2". Now I regret it...

Everything is buried under the pond at the moment, I'll take pics of the filter pit as soon as I can, though it has been unused since july/aug. I'll work on cleaning it all up tomorrow.

At the moment I am running a submersible pump in the pond to a pressure filter to waterfall.

 

[Mucky_Waters]

At the time I did not think that 2" pipe would be an issue, it seemed much easier to cut and work with plus the availability and expense of all the valves and connectors lead me to choose 2". Now I regret it...

That's kind of what I figured. Pretty hard to change now I guess.
I made a similar "mistake" on my first pond, cheaped out and undersized some plumbing that went through a concrete wall, and didn't even put in a bottom drain. The pond was ok, but without a bottom drain it meant I had the ongoing chore of removing all the muck that accumulates on the bottom of the pond manually. It was one day while doing this tedious and messy chore for the umpteenth time that I decided to adopt the name Mucky_Waters, to remind me never to make that mistake again.