Sunday, July 27, 2008

The Bunyip, a home-made water level: People who know me will tell you that I have a penchant for books, courses and tools. My old, wise and bald friend David once generously bought me a laser level as a present. It was a spirit level with a built in laser, which came with its own tripod, all neatly packed in a plastic case. Once unwrapped, I set the level on its tripod and, by rotating the level on its tripod, did a tour of the walls of the living room with the red laser line. I made some faint pencil marks and then checked these (oh, how annoyingly anal I can be) to see how accurate it was. A laser might be accurate enough but it was stymied by the quality of the tripod, so the level changed as it revolved. Not being ungrateful, I promise, but it would be fair to say that this laser was in the DIY class of building equipment. The cheap tripod made it worthless. [I got my money back at the shop and converted it into beer: an even better present … cheers, David.]

More recently, I was helping out our neighbours Paul and Christiane with their renovation when Henri, the electrician, turned up with a top of the range, self-levelling, vertical and horizontal red lines laser, with which he was justly proud. It was a deal more accurate than the one I’ve just described and a whole lot more expensive. Even so, within the context of that building work, I couldn’t see anything that the laser could achieve that a Bunyip water level couldn’t and at a fraction of the price.

Water will find its own level and the Bunyip exploits this. You get hold of a transparent length of pipe and almost fill it up with water, so you can see the level of the water a little bit down from the end of the pipe. Wherever the ends of the pipe are, even out of site of each other, once the water level has settled, it’s at exactly the same level, both ends. You need somebody on the other end of the pipe. When you move the pipe, both of you clamp your thumbs over the end, to avoid spillages. When you’re in position, you need a little coordination to get approximately the right level. Release your thumbs—lots of shouting is in order—and if the level races in one direction, thumbs on quickly and one of you adjust up or down accordingly (try it and you’ll see, an error says a thousand words). With a little patience, you will get the hang of it … I did and I have minimal patience! The level wobbles up and down a bit, once it’s settled the level in front of you is at exactly the same level as that of your partner. If their level is on the datum line, then you can mark off where your level is and you’ve accurately, and very cheaply, transferred the level, which is what Gabrielle and I are doing in the photo at top.

And it works around corners … even a top of the range laser can’t do that, hee hee!


DOT said...

What a lot of pseudo scientific nonsense to disguise the fact that you and Gabrielle are playing hide & seek and you can’t find her.

From the photo it is obvious she is hiding around the corner while you and your mate are looking in completely the wrong place!

Val Grainger said...

Oh Dot you do say dome funny things.....I agree you could have a caption commpetition with that photo!
However the bunyip is a brilliant thing! attach each end to a pole and you can map contours........much easier than an A frame!!!

Magnus said...

Very pleased to find this blog post bunyip level making. We have recently moved to Northern Portugal where we're on a similar venture (land, permaculture plan, renovation, new straw build, stone, lime, earth, etc.). I need to do the contour thing for swales as we're on incline with terraces. But first, i need to measure levels on a bit of river we have with old water mills, for a hydro electric assessment as final part of msc in energy environment studies (from CAT in Wales).

My questions are:
+ how do you prevent air bubbles in the pipe?
+ how do i measure height difference between two spots? I assume I just measure the distance between from the lower datum point to the final point where the water settles... but when i tried, it was a bit out.
Any advice or pointers as to where to find more instructions much appreciated.

Not sure how to receive reply, my email is

Thanks !

Unknown said...

Hi. I have the same question as Moona. How do I know the spot between the two rulers is level?

Stuart and Gabrielle said...

Hello Scrunchiiface,
I answered Moona by email, so I now see his question remains unanswered on this blog.
I fill the tube slowly with a hose to avoid bubbles as much as possible. You can then chase the little ones out by getting someone to hold the ends while you progressively travel along the tube holding your bit up, until you get to the other end and all the air escapes. Tiny little bubbles don;t seem to make any difference at all.
As long as both end are open to atmospheric pressure, they will always be the same height, this is how it works. You start off my putting an original mark a datum, in one place. One person holds their end on this mark. It is the level of the water in the tube that matters, not the end of the tube. You then go to a different place and, talking to the person holding the other end, you move your end up and down until their water level is once more on the datum. Now mark where your level is. These tow marks are now at the same height.
If you want to get a fall, say of 10 cm in a metre, you measure 10 cm down from the datum. Fr subsequent measurements, you can either put all you marks at datum height and measure down 20, 30 etc, for subsequent marks, or use the new mark as your new datum.
I hope this helps!