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Calculate lateral force/pressure of a body water

  1. Sep 24, 2018 #1
    So I'm planning to build an above ground concrete fish pond. The size of the inside of the pond will be (L)2000mm x (W)500mm x (D)500mm. What I want to know before I go any further is will the poured concrete walls hold the pressure of the water inside. So if I know the pressure of water I'll hopefully be able to know how thick to make the walls etc.

    I know there are formulas for this but I'm pretty green horned when it comes to physics: https://en.wikipedia.org/wiki/Hydrostatics#Hydrostatic_pressure.

    Is there someone who would be able to help me out? I'd like to use metric units.
  2. jcsd
  3. Sep 24, 2018 #2


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    Cant help directly with the calc., those measurements are not overly large, I had a tropical fish tank that size made out of 4mm thick glass
  4. Sep 25, 2018 #3
    Ah, good to know. Didn't think it would be a problem but thought it couldn't hurt to double check.
  5. Sep 25, 2018 #4


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    I would say that the hydrostatic forces are negligible compared with the practical possibilities of frost damage or plant roots or ground moving due to drought. A flexible liner should be there as that will avoid problems resulting from small cracks (old carpet underneath it or expensive equivalent from the pond shop). I think you are more likely to lose water through cracks than with a tsunami across your garden. The advantage you have here is that the loading is very steady and you have no shock loads to deal with. Your pond will not be approaching the Hoover Dam in height and that you would, in any case, be considering a wall thickness of more than just one vertical skin of brick or blocks; a radius between floor and walls and a few degrees of slope in towards the top would 'look right'. Also, if you are planning to cap the wall, it could look good with a reasonable thickness so that you can lean on it and get your face close enough to see the inhabitants.. Look at images of ponds on Google and that will give you an idea of what works structurally - also you can choose a design that's pleasing to look at. I have never heard of Pond Wall Failure so I don't think there's anything to worry about.

    PS It's essential that you have some way in and out of it for visitors (unless you just want ornamental fish which I, personally find a bit boring on their own.) But an emergency exit for small mammals to get themselves out would be good for them and good for you to avoid small bodies floating about.

    PPS P = ρgh will give you the hydrostatic pressure at depth h. Bearing in mind that 1Atm corresponds to about 10m of water, your depth of 0.5m gives you just 1/20Atm excess pressure on the floor (and outwards at the bottom too!)
  6. Oct 8, 2018 #5
    If I'm not completely rusty then your pressure comes to about:
    P=1000x9.81x0.5 = 4905 Pascal
    The force acting on the longest wall comes to F=4905 x 2.0x0.5 = 4905 newtons at the centre of pressure.
    I'm not even sure if it will really be that bad because the pressure will be a worst case scenario right at the bottom of the tank. I have to admit that I'm very rusty with these calcs, we did this way back in our second semester (about 10 years ago). I cannot remember what assumptions you're supposed to make.
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