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Removing a big pond

SurreyPM27968SurreyPM27968 Posts: 9
in Problem solving

We inherited a large, natural (unlined) pond (5m x 4m and up to 1.2m deep) in our back garden. We are on heavy clay with a high water table. When we moved in we immediately fenced off the pond as a temporary measure until we decided what to do with the pond. 


Last summer, we consulted with a few experts all gave the same advice, which we followed. We brought a digger in and cleared out the irises and reed and brought in approx 35 tonnes of crushed concrete to help with drainage. This was approx 6 inches below the soil line of the surrounding lawned area. We have left it over the winter and now have a shallow pond for 4-6inches over the crushed concrete. 


Our new step is what I would like opinions with. We intend to add a layer or small pebbles on top of the concrete to raise the level to where the pond water tops out (approx 6 inches). Once this is raked flat, we will cover it with a non-woven (permeable) member and then top with top soil and grass seed. The membrane will keep the top soil from disappearing into the gaps while aiding drainage.  


Does the above sound like a reasonable approach? I want to avoid a boggy mess, do you think this achieves this objective?

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Posts

  • RedwingRedwing Posts: 1,511
    It is very sad to me that you decided to fill in a large natural pond.  There will have been habitat loss.
    Based in Sussex, I garden to encourage as many birds to my garden as possible.
  • SurreyPM27968SurreyPM27968 Posts: 9
    Noted. There wasn’t much wildlife in the pond. Despite the fence, the kids were still able to find a way to get in and we had 3 or 4 incidents where children fell into the water. So the decision to remove was made out of safety rather than anything else. 
  • FairygirlFairygirl Posts: 55,117
    I don't know how well the layer of gravel/pebbles will work, but you may find the level of the new soil will sink over time too, especially if it's wet, so it might be best to wait for few months before seeding, as you might have to add more soil. It's surprising how easily it happens.  :)
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • KT53KT53 Posts: 9,016
    There will be a considerable drop in the soil level as rain percolates through and takes the soil into every little gap in the rubble fill.  When I removed a pond and filled with rubble it was at least a couple of years before the soil level stopped dropping.
  • SurreyPM27968SurreyPM27968 Posts: 9
    Thanks, my thinking is that the presence of a permeable geotextile membrane will prevent soil from falling through the rubble. 
  • thevictorianthevictorian Posts: 1,279
    I wouldn't have thought it's ideal that you still have a pond there. Is this a function of the high water table or is it that the pond still holds water but is now filled with rubble?
  • SurreyPM27968SurreyPM27968 Posts: 9
    This was anticipated actually. When we filled it in the summerwe purposefully didn’t fill it so it was level with the surrounding soil. We left it 6-12 inches lower so that we could see how the drainage copes with the winter rain and to see if there was any further sinking. We knew that there was a phase 2 in summer 2024, where we would further raise the level. 
  • KT53KT53 Posts: 9,016
    SurreyPM27968 said:
    Thanks, my thinking is that the presence of a permeable geotextile membrane will prevent soil from falling through the rubble. 

    The membrane will slow things down but rainwater will still drain in from the surrounding area.
  • FairygirlFairygirl Posts: 55,117
    Yes - the membrane will stop the majority of the soil falling through, but it will still settle and compact, and it will depend on the long term water levels as to how well grass will ultimately thrive. You may have to keep adding soil in future, so it may not be ideal as lawn for regular use.
    It might be better to consider planting the area, or part of it, up with shrubs, which will also soak up a lot of moisture. All you can do is monitor it over time. 
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • Joyce GoldenlilyJoyce Goldenlily Posts: 2,933
    What a shame to have to lose a natural pond. Something some of us would give out eye teeth to have. Did the previous owners put it in to drain the rest of the garden if the water table is high and you are on clay I wonder? You will probably have to top up the dip for several years before it stabilizes, then you may find you have a very boggy garden generally.
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