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Post new topic   Reply to topic    Irish Gardeners Forum Home -> Water features in Ireland, including all aspects of water gardening.

so i've dug a pond


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medieval knievel
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PostPosted: Sun Oct 12, 2014 5:26 pm    Post subject: so i've dug a pond Reply with quote

or a well, as it seems to be turning out.
anyone have any comments on whether some of the roots you can see in the pic might cause me problems?
one thing worth mentioning is that a lot of the roots on the bottom left were from a now-removed (probably) corsican pine, so should not grow any more (you can make out part of the stump at bottom left).
none of the roots are that big, though.

i've created a shelf maybe 4 inches deep around the rounded edge - is that deep enough, or should i make it any deeper? it may not be that obvious from the pic, but there are shelves four inches deeper again at the 'lobes' of the pond.

i still have to get the spirit level out and level off the sides of the pond; there are some undulations to take care of.
the pond is two feet deep at the deepest point.



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vulkan
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PostPosted: Sun Oct 12, 2014 6:17 pm    Post subject: Reply with quote

I can not see the roots that clearly, but any roots should be removed as there is the possibility they may continue to grow. (Better safe than sorry)

Please tell me that is rain water in the bottom, not ground water.

Regarding the shelf, it depends what you want to use it for as to if it is deep enough.
If the shelf is for plants, again it depends on what plant, but to me it looks like any planting baskets will fall off as the shelf is too narrow. (They should be at least 8 inches wide*)

I would also suggest that at 2 feet it is too shallow, since its not uncommon for water to freeze to almost that far, I would make it another 8 - 10 inches deeper,* and its way too small overall for Koi.

Where will the filtration be going?

It should be nice when finished.

* You have to allow for a 2 inch bed of sand and the liner.

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tagwex
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PostPosted: Sun Oct 12, 2014 7:09 pm    Post subject: Reply with quote

When laying water pipes it is the requirement to have the top of the pipe a minimum of 900mm from the surface because in this part of the world that is the level at which no frost action will occur, allegedly. So maybe your pond should be that deep at least.
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medieval knievel
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PostPosted: Sun Oct 12, 2014 8:20 pm    Post subject: Reply with quote

vulkan wrote:
Please tell me that is rain water in the bottom, not ground water.

nope, that's the water table. we have a culverted river somewhere behind the house (about 100 foot away, i'm told) and the water table is higher as a result. it's part of the river wad system in dublin.

it's going to be a wildlife pond, so we're not going to have fish in it; no plans for running water as yet; is that a bad idea?

re the roots; i'm lifting (i.e. tearing up out of the soil where practical) any roots for which this can be done; but where the pond is had a hypericum and the pine right beside it, the first which i've lifted the rootball of, and the second cut to a stump. the roots seem to be mainly associated with those two. and i'll be jumping on any regrowth of the former.

tagwex - the pond is about 40 foot down our back garden, so it should be a distance from any water pipes.

just for scale; the pond is about 8 or 9 foot across (i.e. from the point nearest the bottom of the pic to the top)
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tagwex
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PostPosted: Sun Oct 12, 2014 8:28 pm    Post subject: Reply with quote

You have misunderstood me. In order for the pond water not to freeze completely it needs to be deeper than 900mm.
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Last edited by tagwex on Sun Oct 12, 2014 9:38 pm; edited 1 time in total
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medieval knievel
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PostPosted: Sun Oct 12, 2014 8:39 pm    Post subject: Reply with quote

just reread your post; i had indeed misread you first time around.
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vulkan
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PostPosted: Sun Oct 12, 2014 9:04 pm    Post subject: Reply with quote

medieval knievel wrote:
vulkan wrote:
Please tell me that is rain water in the bottom, not ground water.

nope, that's the water table.


Oh dear. Shocked

Allow me to explain, then you will see the problem


Assuming you line the pond with a liner, as the water table rises where do you suppose it will go?

The weight of the water in the pond will not be heavier than the force of the water coming up, something will have to give.

If its a flexible liner, it will bow inwards (had that happen) if its a rigid liner there is the possibility it will float out of the hole (seen that happen), if its clay lined it will split.


Sorry to be the bearer of bad news, but if the hole is like that now, (and its too shallow) what will it be like when you get heavy rain.?


There are some things you can do.

Move the pond to higher ground (Above the water table)

Build a sump lower than the pond and install a sump pump.

Build a raised pond in the location it is now (filling in the hole first) and surround the pond with soil so it slopes up to the raised pond.

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medieval knievel
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PostPosted: Sun Oct 12, 2014 9:12 pm    Post subject: Reply with quote

we have had (after prolonged heavy rain) flooding in the garden for up to ten days; however, i know someone else who has had this problem without any obvious negative effects on the pond; but what you mention above with the effects on butyl liner (which had been the plan) i had considered adding some stones to the bottom to counteract.
i'm probably going to be pigheaded about it, now that i've dug the pond, and proceed anyway...

i had been talking to one of the newt guys from the irish wildlife trust about the pond occasionally flooding into the garden (lining issues to one side) and he didn't see a problem (for the wildlife), as it's a common occurrence in nature.
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baabamaal
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PostPosted: Mon Oct 13, 2014 11:45 am    Post subject: Reply with quote

I have the same issue with a high water table and a butyl rubber lining- it does indeed bow inward as Vulkan has said, but not by a huge amount in my case. I did add a few hefty stones to weigh it dsown- do remember the displacement issue though, the more stones etc., the less water can fit in the pond. Evaporation in a smallish pond can be fairly rapid in prolonged dry weather and this might be expensive if you are refilling from the mains.
Personally I would take out every bit of root as the weight of the water will press the butyl against any sharp edges and over time this may result in a tear.
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medieval knievel
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PostPosted: Mon Oct 13, 2014 1:11 pm    Post subject: Reply with quote

cheers - i had been planning on lining the pond with sand or maybe an old carpet before putting the butyl in.

the water took several hours to reach the point you can see in the photo, so the seepage is slow enough.
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kindredspirit
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PostPosted: Mon Oct 13, 2014 4:29 pm    Post subject: Reply with quote

I've lots of old carpet, if you want.
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Good guy
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PostPosted: Mon Oct 13, 2014 8:36 pm    Post subject: Reply with quote

My pond is a bit deeper than yours, though the deep area is larger. I've no intention of keeping fish so I just made it deep enough for a couple of small lilies. So far it is working very well. I do think your shelves are on the skimpy side; if it were mine I'd take them all down to the level of what you have made in the corners and leave them wider. You will also have to leave room for something to disguise the edges of the liner. Stones and gravel can be used to adjust the depth for specific plants and will provide hidey-holes for critters. I used carpet as an underlay and I left in place the most insignificant roots. My pond is shaped a bit like the bowl of a spoon and the shallow end is quite extensive and much of it only between six and three inches deep. It is teeming with wildlife. Evaporation does have quite an effect but that is natural. I've tried to hide the liner with stones in places where it might become visible as the water level drops and that also protects it from the sun. I've never felt the need to top it up but then it rains more here than in Dublin!
I hope it all works out for you.
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vulkan
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PostPosted: Tue Oct 14, 2014 10:41 pm    Post subject: Reply with quote

medieval knievel wrote:
cheers - i had been planning on lining the pond with sand or maybe an old carpet before putting the butyl in.

the water took several hours to reach the point you can see in the photo, so the seepage is slow enough.


It may have taken several hours for the ground water to reach that level, but what will you do if it really pours down? The ground water could rise in a very short space of time.
Adding large stones does nothing to keep the liner in place, since rising ground water can lift that too.

Regarding your chat to the "newt guy" I think you will find he miss-understood you.

Yes, it is true that ponds get flooded in nature, that is not the problem you may incur. Your pond problem is the opposite. If the liner gets pushed up by rising ground water, it will force the pond water (and anything in it) out of the pond. That in itself is not too bad while there is water everywhere, the problem for the wildlife occurs as the water level drops, since the wildlife will no longer be in water and is unable to get back to the pond.

Regarding carpet to go under the underlay, be aware that hessian backed carpets rot in a short space of time. Nylon / man made carpets compress after a few months.

Sand does not rot or compress over time.

At the end of the day it is your choice what you do, I am just telling you from a point of experience.

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tagwex
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PostPosted: Tue Oct 14, 2014 11:48 pm    Post subject: Reply with quote

Ground water pressure has to be seen to be believed. Take heed of what you have been advised on. I can only pass on my experiences as a civil engineer, believe if you want to but I have seen ground water move tonnes of material, your little pond is an insignificant amount weight wise and I truly do not mean to be condescending in any way.
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Its my field. Its my child. I nursed it. I nourished it. I saw to its every want. I dug the rocks out of it with my bare hands and I made a living thing of it!

This boy can really sing http://youtu.be/Dgv78D2duBE
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medieval knievel
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PostPosted: Wed Oct 15, 2014 9:43 am    Post subject: Reply with quote

interestingly, the water has almost disappeared; i suspect it was a bit higher than normal due to the very wet weather we had about 10 days ago.

don't worry, i'm taking all advice on board, but at this point i'm probably going to take the chance as we already have the liner (i was given it by my father in law, who has a bigger pond, and there seems to be enough left over for ours), and i've the pond dug now
he has the same issue with high water tables, but seems to have the same experience as baabamaal; it hasn't affected his pond yet. the issue he had with his pond two years ago was that the liner was punctured (he thinks by a heron), so it had to be lifted and replaced.
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