During the time that the workers were digging the pond, I was very busy with work. At least that is my excuse for why the pond isn’t level now. 😉

Over the weekend, I was reading up on a number of resources for digging ponds and discovered this very good PDF about building natural swimming pools. If you are interested at all, I highly recommend the paid 160 page version, but there is a free 30 page version that has a pretty good overview.

Anyway, in there, I learned about the very simple “Bunyip water level” device. Here is a picture of the one I made yesterday:

A Bunyip water level

It is just a plastic water bottle turned upside down with a hole drilled through the cap that allows a clear plastic tube to fit snugly inside. A small air hole is drilled in the other end (used to be the bottom of the bottle, but now that the bottle is upside-down it is facing up). The land is quite large, so I’m using about 30m of tubing. You have to fill up the tube with water and get all of the air bubbles out.

Tip: I found that filling it up with water by sticking the other end of the tube inside a small garden hose and jamming it up about a 1-2 meters into the hose allows the hose to fill it up easily and pushes all the bubbles out at the same time. Watching it is actually like a children’s game of sorts as you watch the end of the water race through the tube along the ground around the loops and all the hairpin turns. (I’ll take my amusement where I can get it.)

Now that the tube and bottle are filled with water…
By holding up the bottle away from the other end of the tube, you will find that the water settles to the same level on the bottle end and the other tube end. This is because the air pressure above the water is the same on both sides (the open end of the tube, and the up-side of the bottle with the small air hole in it). Here is a picture bringing both sides together for demonstration:

Since there is about 30m of tubing between these two points, you can imagine that one could measure exactly the same level even when the two sides are quite far apart.

Tip 2: Given the length of the tube and the amount of water inside, it can easily take 30 seconds for the water level to settle given all of the inertia of the water in between moving around. I found that you can help it settle by stopping the end of the tube with your finger so the air pressure kills the inertia of the water. When you release your finger, it continues moving in the right direction. This keeps it from swinging up and down and overshooting each time. Kind of like dampening a spring.

I was both excited and nervous to try this out to measure the pond that the workers have already dug. The workers already use a similar device for leveling construction within the house, which is just a much shorter tube that they fill with water. But they apparently didn’t think to extend that concept to the digging of the pond. (And to be completely honest, neither did I. No point in blaming the workers here.)

After measurement, it appears that there is a variation of the ground levels that were supposed to be at the same height by up to 1 meter. My target pond water level reference point is a cement cistern that I plan on putting the main water pump in. Here is a picture of the problem:

Water level problems

Unfortunately, a fairly low water level at the cistern in the background results in the water level being above the ground level in the foreground (close to the first house we are building).

The house is actually raised about 1 meter off the ground, and the ground slopes up a bit, so the water level is only about 20cm off the ground at the base of the house, but it would still flood the land. This is obviously not going to work.

So two options remain:

• add about 40cm of soil to the lower sections to raise them up
• destroy the cistern and dig the higher water-level sections down a bit to level them up

Praew and I are partial to the second option.

It is a screw-up any way you look at it. But it should cost us about a week of time and maybe $500 of rework (excavator rental to level the land again and a rebuild of the cistern). This is the biggest screw-up so far, so I consider myself ahead of the curve in this regards. (So far.)
🙂

More updates to come…