Bog filter island in center of a lined pond

[rehreh52]

I have a 12x12 above ground pond built from Juniper posts in a log cabin fashion. (max depth is 24 inches)
I want to create a 3x8 bog filter as an island in the center of the 12x12 pond.
The 3x8 island will be constructed in the same fashion as the 12x12 pond and will "float" in the 12x12 pond; that is, fish will be able to swim under the island.
The island once filled with pea gravel and water will weigh close to 3500 pounds.
I plan to support the bog filter using 8 concrete piers with posts and beams on top of the piers. The 4 beams will be placed 2 feet apart.
I am confident in building a strong enough framework.
The questions I have are: what are the best practices for placing a heavy framework in a pond?
Do you build the framework and then just drape the liner up and over each of the beams? Or would you drape it over all 4 of the beams? And what do you put on top of the beam and the liner so the weight of the bog filter doesn't destroy it?
Or is there some practical way to build the framework on top of the liner? Which would be highly desirable as it would result in a smooth bottom rather than all the draping up and over the beams.
thanks,
rehreh52

 

[Meyer Jordan]

Why not just have a floating island phyto-filter. Will get almost the same results but will eliminate any bulky and heavy support structure.

 

[Lisak1]

This does sound like an engineering nightmare, especially as a retro build. I think someone here designed a pond with an island, but that was a new build.

 

[rehreh52]

Why not just have a floating island phyto-filter. Will get almost the same results but will eliminate any bulky and heavy support structure.

the island will be full of plants and will ge an asthetic centerpiece for the pond.
thanks!

 

[Ruben Miranda]

Hello
First make sure you put a lot of padding under the concreate piers, as that is a lot of whieght on the liner and good cut the liner.

Are you pouring/making your own piers ?
If you are make them a little taller then your pond depth and aviod having wood underwater as they will rot much quicker. And having a big problem down the road.

Remember to put in a easy clean out piping to flush it out and avoid having to take out all the plants and gravel to clean it.

Ruben

 

[Meyer Jordan]

the island will be full of plants and will ge an asthetic centerpiece for the pond.
thanks!

A floating island can be used for aesthetic purposes.
To construct what you are espousing will require footers underneath the liner to support the base of the concrete piles. Several layers of underlayment need to be both below and on top of the liner for protection. If this Island is constructed as planned 3' x 8' and only one foot in depth, the gravel alone will weigh about 1.5 tons. Add to this the weight of the concrete piles, the support beams and the water in the "bog" and you have a considerable amount of weight. Utmost care must be taken to protect the liner.
This is why I suggested the floating island option. These can be constructed to any size and shape and do not require gravel as a substrate for the plants.

 

[Usman]

I have very very small island but i made it from under liner in start , then added some rocks on it with plants , but i think u can create one over liner using some pots or plastic drum or plastic strong pots upside down as base then adding wider container over it as platform then add some rocks stuff , all depends how u can search for rite material
i dont recomend u to add heavy concerete or cement stuff . you dont need platform to come above water rather just it can be below surface of water 6 inches then make border of rocks and fill middle part with a container as bog

 

[rehreh52]

A floating island can be used for aesthetic purposes.
To construct what you are espousing will require footers underneath the liner to support the base of the concrete piles. Several layers of underlayment need to be both below and on top of the liner for protection. If this Island is constructed as planned 3' x 8' and only one foot in depth, the gravel alone will weigh about 1.5 tons. Add to this the weight of the concrete piles, the support beams and the water in the "bog" and you have a considerable amount of weight. Utmost care must be taken to protect the liner.
This is why I suggested the floating island option. These can be constructed to any size and shape and do not require gravel as a substrate for the plants.

My current thinking:
Pour 3x8 concrete pad in soil at bottom of pond
Cover concrete pad with rubber horse stall mat
Install 12x12 liner for the main pond.
Cover the liner above the 3x8 concrete pad with a rubber horse stall mat (so liner is sandwiched between two horse stall mats)
Place cinder blocks on the horse stall mat (double wide for stability) up to a height of 24 inches (just above water line)
Place 5x5 Juniper beams across cinder blocks (you end up with 4 beams held up by cinder blocks). All wood is above water.
Build the 3x8 pond on top of the 4 beams.
Any fatal problems with this approach?

 

[Meyer Jordan]

My current thinking:
Pour 3x8 concrete pad in soil at bottom of pond
Cover concrete pad with rubber horse stall mat
Install 12x12 liner for the main pond.
Cover the liner above the 3x8 concrete pad with a rubber horse stall mat (so liner is sandwiched between two horse stall mats)
Place cinder blocks on the horse stall mat (double wide for stability) up to a height of 24 inches (just above water line)
Place 5x5 Juniper beams across cinder blocks (you end up with 4 beams held up by cinder blocks). All wood is above water.
Build the 3x8 pond on top of the 4 beams.
Any fatal problems with this approach?

That should work in protecting the liner.

 

[Usman]

My current thinking:
Pour 3x8 concrete pad in soil at bottom of pond
Cover concrete pad with rubber horse stall mat
Install 12x12 liner for the main pond.
Cover the liner above the 3x8 concrete pad with a rubber horse stall mat (so liner is sandwiched between two horse stall mats)
Place cinder blocks on the horse stall mat (double wide for stability) up to a height of 24 inches (just above water line)
Place 5x5 Juniper beams across cinder blocks (you end up with 4 beams held up by cinder blocks). All wood is above water.
Build the 3x8 pond on top of the 4 beams.
Any fatal problems with this approach?

are you using beams as border? and what will be the height of concrete pad? whats thickness of linner
seems good