I just read your answers about "Building a raised wall for a pond." Although quite detailed, I am not very physics minded and hope someone will give me a thumbs up or down.

I have a pond that is about 16' x 30', 3 sides will be earthen and stone walls (of which, I am not so concerned) the 4th wall is block and masonry.

The wall I am concerned about is 2 concrete blocks high (16") and about 30' long. The first course is about 2-3" below grade.

I laid 4 courses of decorative wall block (the wall blocks weigh about 23 lbs each) about 4-6" behind the cement block wall, 1 course is below grade. I then filled the gap between the two walls with about 1000 lbs of concrete. The cement block was filled with ground and gravel and 1/2" x 4' rebar driven in each hole.

Is this sufficient of a wall to retain the pond water?

  • Did you back-fill against the back of the wall? From what you described, it sounds like you have got it. I am no expert on this subject, but I think that if the pond is at a relatively shallow depth, then it sounds like it would be fine IMO.
    – lazoDev
    Aug 17, 2011 at 1:44
  • No, the wall will not be back filled. I know that would have been strong enough. This wall is a decorative wall.
    – Stephen
    Aug 19, 2011 at 10:41

1 Answer 1


1 Cubic foot of water equals 62.48 pounds - the trick here is calculating the lateral pressure, but doing a little googling I found the following formula:

R =(62.4)(L)(H squared)/2 (R = pounds force)

The force water exerts is equal both sideways as vertically, so using this calculation we can determine the force that will be exerted against the wall at its lowest exposed point by using the long width of the pond as L and 13" (call it 1.1)

62.4*30*(1.1 ^ 2) all over 2 = approximately 1,133 pounds over 1 square foot of lateral force at ground level, which translates to a pretty measly 7.865 pounds per square inch (1,133/12/12). (If my math is right, and I think it is a TAD low because if you imagine a column of water 1 inch square and 30' high that's 360 inches of water which is 360 cubic inches which is about a gallon and a half, and a gallon is 8 pounds (pints) ("a pint's a pound the world around")

Since your cement block is filled with gravel and rebar and you've got 1k lb concrete between the two wall layers - I'm reasonably certain that your wall strength combined is sufficient. However, to be ABSOLUTELY certain, you should consult with a structural engineer who can do all the complex engineering calculations that go into figuring lateral, axial and compressive strength of concrete, etc...

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