Number and spacing of slits in bog manifold?? How to know?

[nimrod]

So I've got my hole dug. I am putting the liner in today/tomorrow. I've got all the PVC and connectors for my bog manifold. But I need to cut holes in the pipe to allow the dirty water to flow into the bog, right??

But how many holes? My brain is telling me that we choose the widest pipe that our pump can use to maximize flow, and reduce stress on the pump. So the same theory should apply when dealing with the exit area for said water. But if I put too many holes in, the water will all exit early, and the distribution of water exiting into the bog will be uneven. So the ideal scenario is to cut exactly the correct number of slots to allow for 100% of the pressure to dissipate, not higher, not lower. Am I correct in assuming this?

I will also assume it's better to have slightly higher pressure than to have not enough. Which brings me to my second question: following the advice of some of the members here, I have two 90 degree bends at the end of my bog manifold to allow for periodic flushing. I've never really understood how to operate said flushing vents. Do you open them, and shoot water down the manifold backwards? Or do you open them up, and let the pump push water/sludge out of the ends? Because if you are going to do the latter, you would need to make sure there is a bit of pressure built up in the manifold to allow for the pushing of said sludge.

For reference:
~1600 gallon pond (close to 3000 including bog)
-aquaforce 2700 pump
-2" tubing from pump to bog manifold. '
-manifold is ~20 feet of entirely 2" PVC

 

[brokensword]

So I've got my hole dug. I am putting the liner in today/tomorrow. I've got all the PVC and connectors for my bog manifold. But I need to cut holes in the pipe to allow the dirty water to flow into the bog, right??

But how many holes? My brain is telling me that we choose the widest pipe that our pump can use to maximize flow, and reduce stress on the pump. So the same theory should apply when dealing with the exit area for said water. But if I put too many holes in, the water will all exit early, and the distribution of water exiting into the bog will be uneven. So the ideal scenario is to cut exactly the correct number of slots to allow for 100% of the pressure to dissipate, not higher, not lower. Am I correct in assuming this?

I will also assume it's better to have slightly higher pressure than to have not enough. Which brings me to my second question: following the advice of some of the members here, I have two 90 degree bends at the end of my bog manifold to allow for periodic flushing. I've never really understood how to operate said flushing vents. Do you open them, and shoot water down the manifold backwards? Or do you open them up, and let the pump push water/sludge out of the ends? Because if you are going to do the latter, you would need to make sure there is a bit of pressure built up in the manifold to allow for the pushing of said sludge.

For reference:
~1600 gallon pond (close to 3000 including bog)
-aquaforce 2700 pump
-2" tubing from pump to bog manifold. '
-manifold is ~20 feet of entirely 2" PVC

If you can, go larger on the manifold, but it's not necessary. I went 4" (with 1-1/2" inlet) and used corrugated drain tile/piping. You want to 'CUT SLITS' not drill holes as water can then find easier egress. The holes can get clogged up. You cut 1/3 the way through the pipe. I put all my slits facing up, some put the slits pointing down. There's advantages to each but I've not heard of any major issues either way. What you have to realize is as the water exits, it'll fill the empty places low, then eventually find a way up, so not really an issue with spacing, but most will do something like; every 6" at the beginning of the manifold and then closer together the further out you go. I just cut my slits every 6" or so, all the way down. Again, water will always 'win', so it'll get to the end before it starts pushing up, imo. Especially over time as the easier pathways up are slightly clogged, this makes the water seek easier paths and it'll travel whichever way it has to to get up.

There is no 'exact science' to the slits, well, there probably is, but you're not in theoretical world; in the real world, you have a lot of latitude, enough so you can not worry about it.

Okay, re flushing; two schools of thought here. The first is you open the vertical pipe and the pond pump will shoot water out, debris along with it, just as you describe. Now, that only clears the PIPE. What about the underside of your gravel? That's where the main plane of clogging is going to happen (if you use Aquablox or large stone as a first layer; if all pea gravel, no plane will exist). To flush that, the process is a lot different and without installing a 'snorkel' system, you can't easily do it. A snorkel system means you put an auxiliary pump INSIDE the snorkel/vault down to the bottom. This vault is the lowest point of your bog. You then take your bog input pipe and force water FROM THE TOP down into your gravel to disturb that clog layer on the bottom of your pea gravel, or even through your pea gravel. This water will force the crud loose and down into your vault (it's the low point, remember?) and the aux pump pumps it out. You can't do this with a hose (ask me how I know), you must use the pond pump, something of decent volume and force/pressure.

That's why IF you're going to put in a cleanout system like I just outlined, you need to make the bog walls in the shape of a 'V', and have the manifold slope down to a low point, to the vault. This means all the downward pressure with crud heads toward this vault and your aux pump. I've been told by a pro that it typically takes two or three backflushes to get you clean water coming out.

All that said, the idea is you hope you won't NEED to backflush OR flush the manifolds as in the first direction. But, if you do, you're ready; just pick your poison.

 

[nimrod]

There is no 'exact science' to the slits, well, there probably is, but you're not in theoretical world; in the real world, you have a lot of latitude, enough so you can not worry about it.

Okay, yeah. That is what I think I needed to hear. I'm an untrained "engineer" so I tend to overthink things, leading to a lot of inaction.

I've read plenty about the snorkel method of bogs, and the K.I.S.S. method. And after too long overthinking it, I decided that because it's my first pond, and it has to actually EXIST at some point, I better roll with the KISS method. That's why I've opted for the 2" PVC manifold. Currently my bog is 24" deep, and 'perfectly' flat across the bottom. I plan to use some larger stone for the first layer, then pea gravel on top of that. I like the snorkel idea, but I hate all the insanely overpriced plastic tubes that are typically recommended.

I 'm hoping that I can dig a small trench for the manifold pipes (so they will be the lowest point), and cut my slits facing up, so any settling muck won't clog them. Plus any settling muck could potentially be blasted out via the cleanout tubes.

With the amount of sh*t that ducks produce, I am quite nervous, but addy keeps flaunting her no-nonsense bog that just keeps on working, so I am thinking I will roll the dice, and see what happens. I'm keeping the budget as cheap as possible, so I won't have a pond full of heavy ass boulders, so worst case scenario: do over...

 

[brokensword]

Okay, yeah. That is what I think I needed to hear. I'm an untrained "engineer" so I tend to overthink things, leading to a lot of inaction.

I've read plenty about the snorkel method of bogs, and the K.I.S.S. method. And after too long overthinking it, I decided that because it's my first pond, and it has to actually EXIST at some point, I better roll with the KISS method. That's why I've opted for the 2" PVC manifold. Currently my bog is 24" deep, and 'perfectly' flat across the bottom. I plan to use some larger stone for the first layer, then pea gravel on top of that. I like the snorkel idea, but I hate all the insanely overpriced plastic tubes that are typically recommended.

I 'm hoping that I can dig a small trench for the manifold pipes (so they will be the lowest point), and cut my slits facing up, so any settling muck won't clog them. Plus any settling muck could potentially be blasted out via the cleanout tubes.

With the amount of sh*t that ducks produce, I am quite nervous, but addy keeps flaunting her no-nonsense bog that just keeps on working, so I am thinking I will roll the dice, and see what happens. I'm keeping the budget as cheap as possible, so I won't have a pond full of heavy ass boulders, so worst case scenario: do over...

only the muck INSIDE the manifold will be blasted, just know that. Otherwise, you should be good until you test with ducks!

 

[nimrod]

Yeah, I realize that. I just can't think of a simple way to change that without a complete redesign. My hope now is that the pond will be deep enough, and the pump sitting above the bottom of the lowest point will allow any excess sludge to settle before getting sucked into the bog.

How do people typically vacuum out the muck from their pond bottoms?

 

[brokensword]

Yeah, I realize that. I just can't think of a simple way to change that without a complete redesign. My hope now is that the pond will be deep enough, and the pump sitting above the bottom of the lowest point will allow any excess sludge to settle before getting sucked into the bog.

How do people typically vacuum out the muck from their pond bottoms?

you'd have to create something similar to my setup for cleaning both, if you haven't already done the deed!

Yes, keep your pump off the bottom. The problem YOU might encounter is with ducks, the disturbance might be enough to actually keep the debris floating longer/more and your pump WILL suck it in. Now, if you're up for a bit more designing/maintenance, you can make a bog prefilter as I did. It's based on the 'sock filter' for aquariums, but pond-sized. The idea is you have a large sock mesh that catches any large particle (any size you want, actually) before it hits the bog. What this means is you will force water into this barrel with the sock, then the water exiting pours INTO your manifolds. So, you lose the pump force feed because it's all done now via gravity. I'll post some design pics in my showcase, as others have asked before. More engineering, though, and now you have to provide a place for the barrel sock filter (and camo if you don't want to see it).

They use pond vacuums.

 

[nimrod]

Hmmm... I'm not interested in anything out/above the waterline at this point. But it's good to know that there are options for tweaking the filtration as we move along.

Any easy way to measure how clogged your bog gets over time?

sorry, it seems I've got you cornered, and I'm just unloading questions on you. That usually means it's time to actually do some work, and see what happens next. Thanks

 

[brokensword]

Hmmm... I'm not interested in anything out/above the waterline at this point. But it's good to know that there are options for tweaking the filtration as we move along.

Any easy way to measure how clogged your bog gets over time?

sorry, it seems I've got you cornered, and I'm just unloading questions on you. That usually means it's time to actually do some work, and see what happens next. Thanks

heh, too quick to be cornered!!!

no, not really (measuring bog clog) but you'll know it's getting clogged (normal usage so don't worry yet) when the water rises in your bog filter. That's why we suggest you have at least 6" of 'wall' on all sides ABOVE the gravel/weir line. As a bog clogs, the flow will slow. Sheesh, a LOT OF RHYMIN' fer ya in this post! Hey @addy1 ; do I get a bonus for rhyming AND being focussed???? btw, can ya add BC (bog clog) to the acro list? I bet this won't be the last time I use it!!!

 

[GBBUDD]

Okay, yeah. That is what I think I needed to hear. I'm an untrained "engineer" so I tend to overthink things, leading to a lot of inaction.

THE BIGGEST THING IS NOT TO CUT THE PIPE TOO MUCH THAT THE WEIGHT OF THE STONE WILL CRUSH THE PIPE. I recommend every 6 inches and using a circular saw / skill saw cut through the pipe 1/3 it's diamiter. I taped my pipes together and just ran the saw across the pipes . How often is you just want to have enough slots cut that your not so small that the say 3000gph pump only has the volume in slots to allow only 2000 gph out. so too many slots cut is not a problem as the stone is going to place back pressure and allow the water to pretty much come out of the pipe evenly.

Any easy way to measure how clogged your bog gets over time

Oh but there is or there can be . In the matrix bog you have the snorkel and and if inside the snorkel the water line is only say an inch from the top but the snorkel is sticking up a foot above the water level then you have some back up within the bog. some also add a vertical pipe in the peastone bogs same principle just a smaller pipe

 

[bagsmom]

Nimrod - thank you for asking these questions! I plan to get building on my pond this spring, so you have my wheels turning!
GBUDD, I was wondering - relative to your comment about not wanting the weight of the stone to crush the pipe - could a person do something like this to help with the weight of the rocks?
Lay the pipe with slits facing down. Surround with softball size rocks to the top of the pipe (to sort of nestle them in place horizontally.) Then put a few small Aquablox (the shallow depth ones) on top of the pipe - this layer of blocks held in place horizontally with more of the large rocks. Then egg rock and finally a layer of pea gravel.
Did that description make any sense? The idea is to use a few aqua blocks to protect the pipe - but not get so fancy that a perfectly cubical bog dig is needed. Also to avoid trenching in the pipe; the layer of larger rocks could hold the pipe in place the way a trench placement would.
Is this just making unnecessary work?

 

[nimrod]

a vertical pipe in the peastone bogs same principle just a smaller pipe

Would this not just be the same as the cleanouts? It is my understanding that if the ends of the cleanout pipes (vertical) are not capped, that water will prefer that route as the route of least resistance, and you'll end up with a fountain instead of a bog.

How often is you just want to have enough slots cut that your not so small that the say 3000gph pump only has the volume in slots to allow only 2000 gph out. so too many slots cut is not a problem as the stone is going to place back pressure and allow the water to pretty much come out of the pipe evenly.

I have roughly 20ft of 2" pipe in my manifold. One cut every 6 inches yields 40 slits. A 2" diameter pipe has a circumference of ~13". If I cut into a third of the pipe I can estimate that each slit will render a 4" long 'hole' that is the width of a sawblade (1/8"?). This is then ~0.5 square inches of area per cut. 40 of those cuts will get me 20 square inches of egress for the water. That seems like a lot, but I still have no clue if that will dissipate 2700 gallons per hour. Hahah! See what I mean with the overthinking?

 

[GBBUDD]

Would this not just be the same as the cleanouts? It is my understanding that if the ends of the cleanout pipes (vertical) are not capped, that water will prefer that route as the route of least resistance, and you'll end up with a fountain instead of a bog

in time yes but after 4 years i see little if any back up inside my 24 inch clean out as your referring to or snorkel.

See what I mean with the overthinking?

Im school of hard knocks and common sense not sitting down so much using a calc and square root the heck out of the problem. . i looked at is as if i took all the cuts would they completely cover the end of a 2 inch pipe if the cuts were a physical thing. so a 1/16" cut few blades are a true 1/8" any more so i look at it as 32 cuts would be a minimum to cover a 2" pipes opening in volume 16 cuts would equal 1" so 32 cuts . As the wife would say putz logic

 

[GBBUDD]

Nimrod - thank you for asking these questions! I plan to get building on my pond this spring, so you have my wheels turning!
GBUDD, I was wondering - relative to your comment about not wanting the weight of the stone to crush the pipe - could a person do something like this to help with the weight of the rocks?
Lay the pipe with slits facing down. Surround with softball size rocks to the top of the pipe (to sort of nestle them in place horizontally.) Then put a few small Aquablox (the shallow depth ones) on top of the pipe - this layer of blocks held in place horizontally with more of the large rocks. Then egg rock and finally a layer of pea gravel.
Did that description make any sense? The idea is to use a few aqua blocks to protect the pipe - but not get so fancy that a perfectly cubical bog dig is needed. Also to avoid trenching in the pipe; the layer of larger rocks could hold the pipe in place the way a trench placement would.
Is this just making unnecessary work?

Thats the idea alright three things to think about.

With the pipe facing down which is what i did the water pressure if over abundance of slots are not cut will have some water pressure pushing at the epdm liner or what ever you use if the pipe is elevated with a layer or pea or river rock not more then just a covering the rock would take that abuse.

The bottom of the bog should be off level and the pipes be pitched away from the source end of the pipes.

It is my understanding that no bog plants have roots the reach deeper then 18 inches to keep the slots from getting clogged by roots i would lean toward 18 to 24 inches of pea stone or 3/4 river rock

The rock will not crush the pipe so much as if you cut to deep into the pipe more then a 1/3 the pipe will easy snap apart at those cuts . That is what i was referring to as crushing,

 

[brokensword]

Would this not just be the same as the cleanouts? It is my understanding that if the ends of the cleanout pipes (vertical) are not capped, that water will prefer that route as the route of least resistance, and you'll end up with a fountain instead of a bog.

I have roughly 20ft of 2" pipe in my manifold. One cut every 6 inches yields 40 slits. A 2" diameter pipe has a circumference of ~13".

Yes.

ah, no; circumference would be 6.28" (2 x Pi x R)

 

[combatwombat]

@bagsmom: Any aquablocks will help with dispersion, but totally unnecessary for distributing weight. If your pipes are 12"+ under gravel, I can't imagine anything you could ever place on top of your bog could crush the pipe. The deeper they are, the more the load gets distributed from the top.