Expanding / Adding to Existing Pond

tomfranc(Z5 Upstate NY)November 16, 2008

I currently have a 1000 gallon pond which I built 8 years ago. I am interested in expanding the pond. I do not want to remove the pond because the Koi are to large to keep out of the pond for the new construction and I don't want to risk loosing them. I am considering building an adjacent pond about 1 foot higher.

Has anyone done this? Would it be possible to create a spillway or 1 foot falls that would be 6 to 8 foot wide connecting the top pond from the bottom.

Any links with pictures would be helpful.



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Yes, we did it. We built on addition to our existing pond 9 years ago. However, it is on the same plane. We wanted a common pond so that the fish could have more swimming room. Koi love to swim.

The beauty of the way we did it, is that the fish could stay in the pond during construction (it does take several days, as the silicone needs a curing time, before filling with water.)... and if the addition ever springs a leak, the pond water level would only drops down about 8" (knocking on wood, it has never leaked)

The part we added on we call the dog leg section. The dog leg is about 13foot long x 6 foot wide. The dog leg addition changed the shape of the pond from a irregular shaped kidney to an irregular shaped horseshoe.
Here is a photo of the pond in the snow, it is the best way to show the shape.
I'll be happy to tell you exactly the way we did it, if you want your addition to be a common pond.

    Bookmark   November 17, 2008 at 7:27AM
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In front og the arden fairy is where it is peiced together. The pieced section is about 3 foot wide (before the rocks are placed on the edges) after the rocks were put in place the opening is about 2 foot wide. It is about 8" deep where it is seamed, the rest of the dog leg is about 2 foot deep.

Here is the existing pond, you can see the opening to the dog leg, where the fish can pass back and
forth between the main pond and the dog leg.

    Bookmark   November 17, 2008 at 7:39AM
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Here is the photo I was looking for...the koi is swimming from the dog leg (on the left) to the main pond (on the right) I was standing on the small dock when I took this.
All the rocks (under the koi) are covering the seam where the pond is pieced.

Before I go any furthue, you need to tell me if your interested in making a common pond or not.

Here is a link that might be useful: Our Pond website.

    Bookmark   November 17, 2008 at 7:47AM
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In the last picture, is the beautiful white and yellow koi sticking out of the water? It sure looks like it.

Your pictures are always so lovely and your pond is wonderful.

    Bookmark   November 17, 2008 at 3:58PM
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tomfranc(Z5 Upstate NY)


Yes I would be interested in making one common pond. The seaming makes me very nervous. Any further information would be welcome in connecting the 2 ponds. The connection will need to be at least 10 inches deep.


    Bookmark   November 17, 2008 at 4:42PM
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You rock! I can't wait to hear what kind of silicone you used. I'm planning on doing the same exact thing. Awesome!


    Bookmark   November 17, 2008 at 5:09PM
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Thanks Anne, Our fish are top swimmers and very friendly.
They swim on top of the water and often look like their out of the water. :)
Tom and Steve.
First we dug the new dog leg..we made an irregular shape and made it about 13 foot long and 6 foot wide in some sections and a little narrower in other sections. After we had the section ready to fit the liner, we then ...

removed the rocks in the main pond at the section where we were piecing the two liners together.

Then we dropped the water level down about one foot and folded back the existing liner as best we could, and dug out the soil underneath to about 8" down.

Then we cleaned the existing liner with alcohol where we were going to tape and silicone the two pieces together.
(We pieced the pond at the deepest end -- the 3 1/2 foot section)

We cut a strip of liner about 8" wide x 2 1/2 to 3 foot long (more about that later)

after cleaning the existing liner with alcohol, you are now ready to piece the two sections together. This is the tricky part, if the liner were flat on the ground -- it would be easy...but it's not, it's on a curve. We used the tape recommended for piecing two pieces of liner together. It was difficult to get it smooth with all the folds etc...
We then silicon-ed the heck out of it. After the silicone dried, we then silicon-ed the 8" strip of liner, we cut and applied it on top of the seam again -- using silicone as glue as well as liberally applying silicone both edges of the 8 liner strip.

we used both a tube of GE Silicone and a tube of Dupont silicone, (regular silicone, not aquarium silicone--we called Ge and Dupont first, both were non-committal as to if it was safe for fish, but reading between the lines we got the feeling there was nothing harmful in the silicone.

After the recommended drying time for the silicone (can't remember but I think it was about 3 days) we then filled the pond. after a couple of days when we were comfortable that there were no leaks, we covered the pierced liner with rocks.
Also the new dog leg has a shelf all around (with the rocks built up to ground level) just like our main pond.

I think I mentioned that this was all done with the fish in the main pond. When we filled the pond up and the koi had a new section it took them about 5 minutes to go through the passage way and take a swim in the new section.

Any questions, please ask.

    Bookmark   November 17, 2008 at 7:24PM
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I didn't take a lot of photos this year, but here's the dog leg in May when the yellow flag itris are in bloom...
after the bloom we rip out 90 % of the iris cause it takes up too much room. We then put in the young taro.

    Bookmark   November 17, 2008 at 7:43PM
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I too have added on a couple of time now. Here are a couple of pictures. I dug out the expansion leaving a solid wall between it and the existing pond. I lowered the water level as much as I could and not worry about the fish. Got the liners joined and in place and then fought just a little to dig out the wall from under the liner, all in all it was not too bad.

I placed a couple of pieces of pipe under the liner near where I needed to dig out the bank to the existing pond. This gave me room to get under the liner to dig, and also kept the water from flowing into the new part of the pond while I was doing it.

Good Luck !!

    Bookmark   November 17, 2008 at 9:03PM
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Tom, the 10" depth is fine, I forgot to mention that when we overlapped the two liners to be for joined, we overlapped them about 6 inches, and used the seaming tape.

Then we silicon-ed on the 8" strip of liner that we cut.
If you follow this method, you don't have to worry about a leak, cause the water level can only drop to the 8 to 10 inches (at the seam level). The worst senario is that you'll have to start over.
The fish will still be safe,
(assuming your original pond is about 3 foot deep where your seaming it) as they'll still have a couple of feet of water left in the pond..

However, just take your time and try and get the tape on as flat as you can, use lots of silicone and wait the recommended time for the silicone to cure.

    Bookmark   November 18, 2008 at 12:45AM
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Nice work! I noticed that by joing your two ponds, it becomes a more unusual shape (in my opinion making it more attractive than one simple kidney shape). However, in doing that, how is your filtration and flow? Do you get adequate flow throughout without getting any 'dead' spots? My pond is simply shaped, and I'm still getting dead spots.

    Bookmark   November 18, 2008 at 8:36AM
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At first I did not think too much about the dead spot which was created which would be in the area to the right of the large rock sitting in the water in this first picture.

But there was a need to put in a second pump to keep the water moving in the back corner closest to the house. What I did was split the flow and send the majority to the filter and the rest to a rock I drilled out for a water feature. That took care of the problem.

We also did about a 6" overlap of the liners, used both the 2 sided sealing tape, and also a 6" sealing tape over the top of that seam, as well the silicone sealer along those edges.... might of been overkill. but no leaks.

We are thinking of running a stream from this pond in an area close to the house, around the back of the house to the back deck where we want to have a small pond and fountain. From there we would pump the water back to the filter in the front yard. That will take care of the dead area I created when adding on this last time..Oh Boy More digging !
In hindsight I should of made sure the bottom was sloped so there was no "chamber" created and no dead spot. Would of been cheaper then running 2 pumps.

    Bookmark   November 18, 2008 at 7:30PM
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I think thats what I'm going to end up doing too.. running a second pump.

I really like your bubbling rock. Looks neat and probably provides alot of extra aeration...

By the way, how deep is your pond at the deepest point?

    Bookmark   November 18, 2008 at 8:14PM
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The deepest section is just over 4 feet deep. The rock is easy to drill, should be able to rent the drill and the bit at most equipment rental places. I drilled a 3/4" hole in this one, easier to drill then concrete.

    Bookmark   November 18, 2008 at 8:34PM
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keithw(Zone 8)

I added a second pond above my first pond, overlapped the liner from the top pond into the lower, and created a waterfall from the top pond to the bottom. I have one pump that pumps from the bottom pond into the top. It has worked great for a few years but if you go this route make sure to put a check valve in the pipe somewhere. Otherwise if you lose power, you will create a siphon and the top pond will drain down into the lower and overflow it until the levels match. I learned this the hard way!

    Bookmark   November 19, 2008 at 8:04AM
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tomfranc(Z5 Upstate NY)

Thank you all for the information. I feel much more comfortable about doing this in the spring.

Stay warm,

    Bookmark   November 22, 2008 at 5:58PM
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That's fascinating, Joann. Thanks for posting this. I've been considering enlarging my pond eventually, and wasn't sure how I wanted to go about it without ripping out the existing liner and replacing it, but this gives me another option to think about.

I'm going to have to bookmark this thread for future reference!

    Bookmark   November 22, 2008 at 11:55PM
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