Beginning Bog Building

[Lynnski]

Can anyone point me toward a thread or video about building a bog from the beginning of the project? I've found excellent discussions on how folks have added a bog or fixed the berm on an existing bog, but we're starting from scratch. Our ground is fairly level, and we'll need the filtration bog to be raised so we can create a stream to waterfall into a pond close to the patio. Trying to understand if the bog's edges can be built/created without more rock. We'll need lots of stone for the stream and the pond, but would like the bog to transition to a planted soil slope... without stone if that's possible. Thanks

 

[mrsclem]

Bog building, also called upflow filter, eco filter, wetland filter

I was asked to start a thread on how to build a bog. This is my rendition on bog building 101............. Building a bog: Before you decide to build a bog, you need to know what you want its primary purpose to be. Total pond filtration bog filtration combined with another filter. If you...

www.gardenpondforum.com

 

[combatwombat]

Not sure about a video that suits your specific scenario, but if you’re up for seaming your liners, you only need to come up another 6” or so to account for freeboard around the bog edge. So, a pure soil retaining wall would probably need to be around 24” wide or wider to make a 6” height look good. If you have 4’ to spare, that should get you there.

 

[Jhn]

To add to c.w.’s post. Couple ways to go about it, if you dig your bog down, use all the excavated dirt around the edges to berm it up to raise the height above that of the pond.

I have two bogs on either end of my pond, one is put in just like I explained above. The other one I used 6”x6”s to raise the bog up, inter locking the corners and pinning it down with rebar and 12” 100d nails, then disguised it with sandstone, some dirt and faced the top with ipe, now you can’t even tell the wood is there. This bog needed to come way up and I didn’t have room to berm dirt up. Just be sure to use lumber rated for ground contact if you go that route, and not the crap the big box stores sell.

 

[GBBUDD]

Though I too used wood to build up my bog , due to it was a rebuild . I strongly suggest concrete block as the build up or a dirt berm as @Jhn suggested. those two products will last and last with no maintenance. depending on where you are it can be an incredibly easy thing to build. if your in a cold climate area it can become a bit more of a challenge. There are two different yet similar bog types. A matrix bog or a pea stone bog.

 

[Lynnski]

Not sure about a video that suits your specific scenario, but if you’re up for seaming your liners, you only need to come up another 6” or so to account for freeboard around the bog edge. So, a pure soil retaining wall would probably need to be around 24” wide or wider to make a 6” height look good. If you have 4’ to spare, that should get you there.

Thanks for this, @combatwombat. I'm afraid I'm too new at this to understand some of what you're suggesting, tho. What is "freeboard" in this context? Is that the 6 inches in height above the pea gravel and water in the bog? Don't I need to build the bog up higher so that it can feed a downhill stream and waterfall?

I figured I'd be overlapping the liners from the different parts (bog/stream/pond) of the system, but you mentioned seaming the liners. Is there a specific issue related to seams if using a pure soil retaining wall?

In another post you mentioned geo-fabric bags that could be filled with native soil then planted. Are you talking about what gardeners call Grow Bags? That sounds very promising for my purposes. I could build a 2' slope around the bog using grow bags, but I can't picture how I would I anchor the extra liner at the top of the bog.

Thanks for your patience with a newbie!

 

[combatwombat]

Thanks for this, @combatwombat.

You bet!

What is "freeboard" in this context? Is that the 6 inches in height above the pea gravel and water in the bog?

Yes, exactly. Wherever your water level in the bog ends up, you want at least 6" more liner above that to accommodate a rising water level as plants grow thick and dam up the flow.

Don't I need to build the bog up higher so that it can feed a downhill stream and waterfall?

You don't technically need to. You can put it anywhere and at any elevation, really. It's most common to build it up above the pond and waterfall back because you get a nice stream/waterfall out of it. But it's not required. I have a bog just like that. I also have a "bog filter" in the bottom of my pond. 6" of sand over 2" slotted pipe. No plants, obviously.

I figured I'd be overlapping the liners from the different parts (bog/stream/pond) of the system, but you mentioned seaming the liners. Is there a specific issue related to seams if using a pure soil retaining wall?

No, seaming doesn't have anything to do with your retaining walls. Seaming the liners together would just allow you to lower the spillway of the bog closer to water level of the pond (or level with the pond) if you didn't have the space to build a soil berm. To do an overlap, you need the spillway of the bog liner to be a minimum 6" higher in elevation than the water level of the pond to avoid leaks between the liners. If you can't get that elevation, then you must seam to achieve water tightness.

So if you want to overlap, you'll need your soil berm to be at least 1' tall, which means you'll need at least 4' to each side of the bog to achieve a natural looking berm. 5' is probably better.

In another post you mentioned geo-fabric bags that could be filled with native soil then planted. Are you talking about what gardeners call Grow Bags? That sounds very promising for my purposes.

You've been doing your homework! I just used $0.50 sandbags. Grow bags would be a lot better. If you like that look, you should go for it. I think it could be really cool.

I could build a 2' slope around the bog using grow bags, but I can't picture how I would I anchor the extra liner at the top of the bog.

You could either rock the walls of the bog, placing small boulders over the gravel (or having a shelf outside of the gravel but inside the liner) and the rocks would hold up the liner. Or you could add an extra course of grow bags and sandwich the edge of the liner between the top bag and the one below it just like many people do with other types of retaining walls. Or you could even glue the back of the liner to the bag or, if you're high enough above max water level, even pound some spikes through the liner into the bags. Lots of options.

 

[CometKeith]

Thanks for this, @combatwombat. I'm afraid I'm too new at this to understand some of what you're suggesting, tho. What is "freeboard" in this context? Is that the 6 inches in height above the pea gravel and water in the bog? Don't I need to build the bog up higher so that it can feed a downhill stream and waterfall?

I figured I'd be overlapping the liners from the different parts (bog/stream/pond) of the system, but you mentioned seaming the liners. Is there a specific issue related to seams if using a pure soil retaining wall?r again I would remove all the fish and water before building the wall

In another post you mentioned geo-fabric bags that could be filled with native soil then planted. Are you talking about what gardeners call Grow Bags? That sounds very promising for my purposes. I could build a 2' slope around the bog using grow bags, but I can't picture how I would I anchor the extra liner at the top of the bog.

Thanks for your patience with a newbie!

Hey Lynnski and welcome to GPF. There are so many ways to build a bog. Another way to look at it is you are building a “wetland”. Most bog build instructions want you to build the bog higher than the pond to create a waterfall, but that is not even necessary and it’s very common in professional installations to make it fairly level so you don’t see where the “wetland“ ends and the pond begins. You can have it the same water level as the pond and let the water mix freely between the two. You just need to install the wall between the bog and pond so gravel doesn’t fall into the pond. You can use some heavy rocks to keep the gravel in where the two are separated. Your bog punp will slowly push the clean water into the pond. If you ever need to add water to your pond it will raise both the pond and bog water and there is no harm to that. Also there are no rules that you can’t go deeper with the rocks and gravel in the bog and you can have it the same depth as the pond if you want or less if that’s easier. I actually built my bog in my pond. I divided about 20% of my pond and designated it as my bog. I lowered the water level a lot and built a stone wall dividing the two and put down a new liner inside the new bog and over the old liner in that section of the pond. After adding piping and a pump and stone/ gravel/ plants and refilling the pond with water I had a working bog. If I would redo it over again I would remove all the water and fish first before building the wall as my pond “expert” suggested! Luckily I did it over a few hot days and didn’t mind standing in it as I was building the wall.

 

[Lynnski]

How does this sound for constructing a filtration bog without using rock? Currently the area is level. The soil is very compacted. We will have more soil from the pond dig than we know what to do with, and loads of plants. Here's the plan:

Create the outer shape of the bog using 2 courses of cinder blocks. Dump soil from the pond dig all around the outside of the cinder block shape. Tamp as we go, shaping a gradual slope out from the raised bog. Top the cinder block shape with underlayment, then with EPDM liner. Place grow bags filled with soil on top of the liner, staking them in place (without staking the liner). Dump more soil onto the rest of the slope. Plant the slope and the grow bags.

Questions: Does this sound like it would work?What size grow bags—5, 7, or 10 gallon? Would rebar or mortar be necessary to secure the cinder blocks? Is there a cheaper way to do the job? Any other thoughts, suggestions, or alarm bells? Thanks

 

[combatwombat]

How does this sound for constructing a filtration bog without using rock? Currently the area is level. The soil is very compacted. We will have more soil from the pond dig than we know what to do with, and loads of plants. Here's the plan:

Create the outer shape of the bog using 2 courses of cinder blocks. Dump soil from the pond dig all around the outside of the cinder block shape. Tamp as we go, shaping a gradual slope out from the raised bog. Top the cinder block shape with underlayment, then with EPDM liner. Place grow bags filled with soil on top of the liner, staking them in place (without staking the liner). Dump more soil onto the rest of the slope. Plant the slope and the grow bags.

Questions: Does this sound like it would work?What size grow bags—5, 7, or 10 gallon? Would rebar or mortar be necessary to secure the cinder blocks? Is there a cheaper way to do the job? Any other thoughts, suggestions, or alarm bells? Thanks

I like it. Assuming this will be a shallow pea gravel type of bog and the 2 courses of block will be your total depth? @GBBUDD would tell you to round the top edge of the blocks facing the liner and add extra fabric there for puncture/abrasion protection.

2 courses of blocks is only 16" I think. That gives you 12" of gravel and 4" max of freeboard. Not enough for long-term safety. I would dig a 8" deep footing, fill and tamp w/ 4" of gravel, and do 3 courses of block. That will make your wall stronger and will get you 8" of freeboard.

I'd use the biggest grow bags you can get. More stable.

I'll let someone else comment on strengthening the wall as I've never worked with cinder blocks. If you're building a berm, though, I'm not sure you even need them.

 

[Lynnski]

I was thinking of the grow bags as part of the retaining berm, but of course they would be above the liner and won't contribute any functional height. * head slap* Great example of why it's important to share plans with others!

 

[Lynnski]

Grow bag sizes:

1 Gallon - 5.9"(H) × 7.8"(D)

2 Gallon - 7”(H) × 9.8"(D)

3 Gallon - 9.1"(H) × 10.2"(D)

5 Gallon - 10”(H) × 12.6"(D)

7 Gallon - 12"(H) × 13.6"(D)

10 Gallon - 12”(H) × 16"(D)

15 Gallon - 14.4”(H) × 17.4"(D)

20 Gallon - 14.5"(H) × 20.5"(D)

 

[Lynnski]

A typical loose sample of fairly dry topsoil weighs just under 8 pounds. One question is what size bags to use to hold down the liner on top of the underlayment/liner sandwich. Is bigger better because it's heavier, or is smaller better because a bottom that's closer to the block's size will be more secure atop the block?


(Soil weight: 1600 pounds per cubic yard. There are 27 cubic feet in a yard and 7.48 gallons in a cubic foot. 1600/27=59.26 pounds a cubic foot. 59.26/7.48=7.92 pounds per gallon.)

 

[GBBUDD]

Sorry I'm not familiar with grow bags

 

[combatwombat]

I don’t think it’s going to matter much what size bag you use.

@GBBUDD: Think of them like a poly sandbag, but made out of felt underlayment material.