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Evaporation or leak?

A client of mine had a company come and dig a large pond.

Over the space of about 3 months, it was virtually dry in the summer. Could this really be down to evaporation, or is it more likely to have a leak?

Before:

After:

To fill it, I had a 3" pump going most of the day, so many 1,000's of litres have disappeared.

I have read on the internet, that for a pool, 1/4" a day could be lost due to evaporation, but for outside, it depends on average wind speed, temperature, etc for an accurate calculation, which is pretty much impossible. It also describes a "bucket test" - put a bucket in so that it is under water, then monitor whether the level of the bucket drops at the same rate that the pool does, as evaporation should be the same for both - does that sound reasonable for a pond?

As my visits to this client have just resumed, I went there about 4 weeks ago, and it was a foot or so down, but this week, it was pretty much as the second photo - we have not had any rain to speak of for weeks down here, and it is topped up from the rainwater run-off from the roof of the property.

The company that installed it are being very cagey about  coming back to site, and are just quoting that they have seen the same at a number of other sites, so is all down to the lack of rainfall in the summer. The lining is some sort of clay impregnated rubber, which sounded very impressive when they were talking about its self-healing characteristics, and it has a deep layer of soil on top of the liner.

I would be interested to know what others would use as a rule of thumb for acceptable water loss.

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Replies

  • PRO
    Leak
  • the photos will not open for me but I dug a pond (by hand) 30ft diameter about 3ft deep has no top up water into it.  it was lined with sand, fleece and a bitumen liner and in mid summer it will go down about 6 ins sometimes in winter it will overflow if there is a lot of rain so I think there is a leak    

  • Have been to the pond today, and it has gone down 2.5" in 7 days. There has been no top up rain this week, so nothing replacing water. Given the temperature and time of year, that seems too much for evaporation to me - any one any thoughts if that is acceptable?
  • You can test it by putting a ruler as a depth gauge. Then you need to top up & then measure the depth at regular intervals.  Leaks from evaporation will vary whereas the leak will be fairly constant until the level drops significantly. 

    If the rate of loss drops suddenly then it indicates that the leak is at that level.  Is there a pump & have you checked for leaks in the pump circuit ?

    • I have made up a gauge and put it in, which is what gave me the 2.5" in a week loss. We are expecting a little rain next week, which should top it up a little, but I'll see on my next visit.

      There is no pump or anything else that could be leaking.

      2.5" a week seems too high to me, but really looking for advice as to what should be acceptable.

      • I am in Ireland so don't know exactly how the weather has been there but it sound feasible especially with sun & wind. It's certainly not enough to think about a repair which with that design sounds impossible.

        I would just fit an automatic top up to keep the level steady

  • PRO
    A farm I do work at has a large pond dug around ten years ago that doesn't have a liner.<br/>
    <br/>
    When it was dug it the excavator when through numerous land drains that are roughly halfway down the pond, initially the pond filled with water then the level dropped to that of the land drains as the excavator had merely covered the ends on the lower outlet drains and the water worked its way through. So after a few weeks the excavator was brought back to site to dig a trench several feet away from the lower side of the pond to break through the drains then ram the excavated spoil back into the trench to plug the drains.<br/>
    <br/>
    Now it looks like the water has worked its way through again and the water is back down to the drain level. Actually identifying where the leak is, is not that obvious though there is a suspect patch of ground that has holes in it, so if dug out and puddled with clay may resolve the issue.<br/>
    <br/>
    In your case the liner may be hiding the problem with the water working up through the soil within the pond to a leak in the liner, if the water is working its way out through a land drain system digging a trench and sealing them may help, but it depends on the soil type and if there are land drains. Presumably the liner was installed as the soil is loose and porous, so this may not be an option.<br/>
    <br/>
    Andy
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