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Measuring the water level in a deep well, the easy way

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  • Measuring the water level in a deep well, the easy way

    We have had rain like we haven't seen in decades. A couple of days ago our water suddenly turned cloudy and rusty. I had a pretty good idea of what happened but to confirm it I needed to know what the water level is in the well. In the past I have dropped in a bob on a line but that is tedious and somewhat uncertain because of the clutter of wires, rope and pipe. While I was removing the cap on the well with a hammer to tap it loose I could very clearly hear the tapping echoing off the water surface below. I immediately realized that I could measure the level using an oscilloscope and a microphone.

    Instead of hauling out my "real" analog o-scope I downloaded a decent one last night and installed it on my netbook. Plugged in a regular mic and ready to go. I pulled off the well cap, stuck the mic in over the edge and replaced the cap. Set up the scope for single trigger with a sweep of about half a second and tapped on the cover with a hammer. With only a couple of adjustments it gave a perfect reading of the travel time down and up again with a weak secondary echo from another bounce.



    Travel time is about 230 milliseconds divided by two gives 115. Speed of sound at 7 C is 337 metres per second. Do the math, convert to feet and the water level is about 126 feet down give or take maybe 5 feet. That corresponds with the depth of the casing which is listed in the well log as around 125 feet. Below 100 feet it is all solid rock. The rust is because the water has come up to the casing and dissolved years of rust since it hasn't been that high in more than a decade.

    Now all I have to do is install a microphone permanently with a small preamp and install a small loud speaker with both connected to the sound card a cable to the house. Then I can use the computer and measure the level anytime I want. I'll write a utility to take the sound card mike input and convert it directly to a depth value. Since the temperature of the water and air in the well never changes it will only need calibration once.

    I forgot to mention that the well is 350 feet deep with the pump at about 330. That gives us 200 feet of drawdown which is good because it is a very low flow rate well.
    Last edited by Evan; 06-21-2011, 01:33 AM.
    Free software for calculating bolt circles and similar: Click Here

  • #2
    Nice trick. Maybe an alternative is one of those crappy little 'rangefinders'

    Same idea. just using ultrasonics.

    On a site note, I still see the old sticks at gas stations, and recently at a hospital near thier reserve diesel tank even though they had some fancy gauge on it..
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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    • #3
      Very neat idea, Evan.

      You'll likely have to choose your speaker and mike carefully, as I assume there would be high humidity and condensation to account for.
      For just a little more, you can do it yourself!

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      • #4
        Clever! Simple and elegant. Since you know the depth of the well, locating the top of the water column gives you the amount of water.

        I once saw a guy measure how much water was in an unknown well. He dropped a pressure transducer on a long wire to the bottom of the well and measured the pressure exerted by the water column. From that and the fact that water pressure increases 0.43 lb/foot, figuring the amount of water was easy.
        ----------
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        • #5
          Neat trick.

          Could you write an app that periodically takes readings then notifies you when the level is a few feet from the casing so that you can pump it down a bit?
          Peter - novice home machinist, modern motorcycle enthusiast.

          Denford Viceroy 280 Synchro (11 x 24)
          Herbert 0V adapted to R8 by 'Sir John'.
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          • #6
            Something similar has been used since time immemorial in the oilfield, to measure fluid levels in the annulus:

            http://www.echometer.com/products/model_m/index.html

            Ian
            All of the gear, no idea...

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            • #7
              I am much more interested in stopping the pump before it runs out of water. Either way, it can be easily controlled by a very low powered computer or even a fairly simple dedicated circuit that measures the time delay via a few logic chips and a time base.

              I checked out this idea after it occurred to me and there are a few commercial units to do the same thing. However, they start at $800 which is ridiculous given how easy it is using equipment a third the price. It sounds like to me that an app for a netbook with a fancy looking display screen might be a very saleable item. It would probably be best to sell it with a standard microphone to reduce calibration issues and to make it harder for people to copy. It would be especially useful to use a USB microphone since then the app could be locked to the manufacturers USB ID number.
              Free software for calculating bolt circles and similar: Click Here

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              • #8
                If you have line of sight to the water surface I'd expect you could simply measure the distance to the water using an out of the box laser measuring system. While the precise details are a bit vague, it now being half a lifetime ago, the principle of using red and green lasers was being used down here for creating marine charts from aircraft, clearly an enormously faster process than traditional methods. IIRC the red laser was reflected from the sea surface, and provided a very accurate aircraft height. Meanwhile the green laser penetrated the surface and mapped the ocean floor. Unfortunately I don't have very good Internet access to start searching, but think this is correct.

                Pete

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                • #9
                  Deep wells are often crooked and even if straight, the cables, ropes and pipe are in the way. I cannot see the water reflection in mine even with a powerful light.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Evan,

                    With not too much extra effort you could use the same transducer for both send and receive (thus saving the cost of a mic and extra wiring)

                    Bill

                    Last edited by BillTodd; 06-21-2011, 09:49 AM.

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                    • #11
                      I wouldn't expect to see a water reflection from a torch down a deep well at the best of times! However as I said, if it has line of sight I'd certainly be trying a laser measure before I dedicated a PC and screwed around with a permanent sonic based setup. It could be that the perfectly still water surface Won't reflect even a red laser effectively anyway, the mapping LIDAR was out in the real world and the sea surface was never perfect, not in laser terms anyway. However now you know the water depth it would be an interesting experiment to try to see if you could get a range.

                      200 ft pfft that's not deep! Some of the inland bores I used to go to were over a thousand!! edit: whoops, you guys are AmericaniZing me, on reading that back, that little sub-note should have read over a thousand metres bore depth. Completely OT, but the Great Artesian Basin is fascinating ... Well if you like splashing around in 2 million year old water (excuse the pun)
                      Last edited by PeteF; 06-21-2011, 09:27 AM.

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                      • #12
                        Chemistry and a LOL

                        Originally posted by Evan
                        I immediately realized that I could measure the level using an oscilloscope and a microphone.
                        I LOL'd because right up to that point I figured the way to do it is run the water thru a friend's employer's water analysis lab equipment and then match the ratio of iron and other elements to a list of well casing steels... He claims a "real lab" can trivially not only tell what kind of pipes are in a house/well but also roughly how old they are, probably based on corrosion and manufacturing byproduct levels. The microphone and echo bit is also cool.

                        Now here's an idea for you, have you ever considered making an acoustic radar using an old stereo system? Bounce sound off clouds, maybe airplanes? I've always wanted to try that but have never gotten around to it. The other thing to try is stereo microphones with one on each end of the property, and do a directional phase analysis of distant thunder, deer hunter gunshots, unmuffled cars, etc, although thats gonna take a lot fancier software.

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                        • #13
                          Our big well runs out of water all the time in dry summers after filling up trucks in the morning.
                          Andy

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                          • #14
                            Robotic apps

                            HiYa..

                            Okay.. a digital ruler is so cheeap these days. ($35). why bother?? There is one with a usb port
                            I wanted one for a positioner and building scanner. $700.. right now.. They will get cheaper.
                            Excuse me, I farted.

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                            • #15
                              Evan,

                              Here in Michigan we have also been deluged with rain for months. Our lake is over a foot higher than I have ever seen it in the 27 years we have owned our cottage, and about two feet over normal.

                              Here at home I have noticed that our water is starting to have a smell to it. I wonder if the water table has risen and gotten into some smelly area. The water has never smelled before. It is only a 50 foot deep well.

                              Brian
                              OPEN EYES, OPEN EARS, OPEN MIND

                              THINK HARDER

                              BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

                              MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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