Transforming old watermill basin into natural pond?

As some of you may know, my husband and I have been for the past year, slowly restoring and rebuilding a historic watermill; where a decent part of the original mill structure (not the machinery) has stayed intact; although in need of maintenance.

Lately we have been eyeing the water wheel basin, and have been wondering about if and how we could transform it into a natural pond.
The basin is constructed against the stone fundament of the mill (our soon to be house). So the walls of the basin are old dry stacked walls (with lots of ferns and mosses growing on them).
The bottom of the basin is currently filled with sediment and debris from the build of the house (so chunks of plaster and cement that have fallen down, broken roofing tiles etc), so the holding capacity is currently rather low because of all of this stuff that needs to be shoveler out first. I don’t know yet if the bottom of the basin is just soil or if I’ll eventually hit a stone floor once I start shovelling.

The basin has two overflows; one the original aquaduct which led the water underneath the house (but we gave no idea where the water goes to (if anywhere at all) as we don’t have plans of the original mill structure); the other is a cement pipe that overflows back into the river. We would like to prevent the water from overflowing under the house (so we might wall off the aquaduct some more), and use the pipe as the overflow.

Currently the basin is being fed by springwater which the previous owner diverted to the wheel, which provides a year round flow of water, but significantly more in winter then in summer.
In the future we might connect the wheel back up with the river as it was originally; which would mean a much larger amount of water passing through.
The basin is about 5 feet (1,5 meters) by 16 feet (5m). We would hope to get a water level of about 2 feet deep.

The basin is on the north side of the house and takes little to no direct sunlight. In winter the waterlevel appears to be ok with the higher flow of springwater, but in summer it seems like the basin isn’t adequately sealed to hold all the water as it seems to be sinking in the ground more.

We would love to have a pond with a more or less stable waterlevel some waterplants (maybe grow some duckweed for our ducks) and maybe some frog or fish. The quality of both the rivierwater and the springwater seems impeccable based on the abundance of fauna living in it (a couple of which are used as indicators of water quality). The plants and fish would need to be able to live in relative shade and should be able to endure some cascading of water due to the water being thrown over the waterwheel. At least I suppose this would mean the water will be nicely oxygenated?

I might consider giving my small flock of 6 or so ducks and 2 geese occasional short supervised access to the pond if this could be beneficial to both the ducks and the pond life (fertiliser for the plants and fish?)

I have no experience whatsoever with building ponds. Does it seem viable to transform a waterwheel basin into a natural pond? And if so, how should I best go about sealing the pond naturally?
What plants and fish could live in these circumstances that could also help to create a natural balance in the pond? And would it be a good idea to give ducks and geese short occasional access?

I’d love to hear your ideas!

Just bumping this post in the hopes someone sees this who can help :-)

My main worry to begin with is how I could seal this pond without using plastic. The sides of the pond are drystacked rock backed by soil. I know you can use clay to seal a pond, but with the drystacked sides I don’t know how that would work. For now the basin holds some water, but it is clear that it is also loosing quite a bit, as there is a constant influx of water while the water level itself remains more or less the same.

Here’s a little update. I hope somebody sees this and has any insight in to how I could work with this.

Recently we’ve had half a meter of snow, and now several days of thaw and rain, hugely increasing the flow of water towards our basin.
The water in the basin has now reached the overflow mark, but the basin itself is obviously leaking as a sieve. The only reason the water is as high as it is is because of the huge amount of water coming in.
Thanks to the snow melting where water is flowing it was easy to see where the water was leaking from the basin. After clearing some sods of grass, I could see that the water was actually leaking from underneath the stone basin wall (and not from the concrete overflow pipe as I initially thought. Seeing this is a little bit disheartening, because this amount of water leaking must mean that an underground channel has formed, right? I’m guessing this isn’t something easily fixed with adding clay to seal the basin naturally, as ‘I’m guessing the walls of the basin are drystacked walls backfilled with earth and rocks. I have no idea how to even begin sealing this. Would pond lining be a bad idea? Are there any alternatives to seal this at least somewhat to maintain water level in the drier periods?

Below you can find some videos I made to show the flow, leaking and location of the basin.


The current flow we’re getting. Ignore the insulation foam floating around, it blew into the basin by wind, and we’ve been slowly trying to sieve it out bit by bit.


Close up from where the water from the basin seems out of the ground at a lower elevation beneath the basin. As you can see, the water comes from under the stone wall retaining the basin, not from under the cement drain pipe.


Video showing the location of the basin with the leak flowing into the creek below. The overflow of the basin also fills a nice little gravity fed fountain. This is the first time the water level has been high enough to trigger the water fountain, so I am thrilled about that! I hope to retain the water level at this night so the fountain is always running from now on.

Any ideas are welcome!

I googled for Mill pond repairs and found these;
Mill pond repair UK

There will be information somewhere in the world about your issue.
As a Civil Engineer I would research how they may have been constructed, and from that some ideas will arise.
There may well be some group that specialises in helping with this issue.
So far I cannot find them, but I will keep looking.

I may have hit gold.
My initial thoughts were to think about lining the stone work with clay, since that may seal it.
It seems that is the solution, along with removal plants etc that will causes leaks along the roots.

The `dry' side of the embankment should be regularly inspected for danger signs such as unaccountable wetness, or water trickling through or under
the dam.
Immediate steps should be taken to remedy the problem. If the flow seems to be increasing before remedial work can be put in place, it is strongly
recommended that the pond be drained. Provided that the seepage rate was small, it is probable that no permanent damage will have been done to the dam
structure, the problem having been resolved by draining the pond. The area of the pond in the vicinity of the leakage points should be treated by cleaning
out any deposits containing plant growth and a layer of clay some 2" (approx. 50 mm) thick should be `puddled' over the area to seal it.
It would also be a wise precaution to seek the advice of an expert as to the correct course of action.
Puddling should be done with a type of clay which becomes impervious when worked with sufficient water to form a stiff `dough like' consistency.
The material is then spread and pressed (puddled) over and around the area through which the water appears to be escaping. If the puddling is allowed to
dry out, it may crack  and lose its sealing quality.
Trees should not be allowed to grow on or close to a dam as their roots can disturb and loosen the structure, leading to leakage; neither should any dead
roots be tolerated, as,when rotted, they can provide water channels through the dam. There is also the possibility of a tree blowing over, taking the dam with it.

This was obtained from a publication Principles and Practise of water mill repair

To S. Bard, your property is just amazing. I would sit and listen to that water trickling (or rushing by) all day long and forget to do my chores. I wonder how your projects have come along since these posts? What a fantastic adventure you have embarked upon. Wishing you and yours all the best, thanks for sharing your beautiful land with us.