Water level measurement for deep artesian bore

[joy56]

Hello,

I was hoping to get some ideas about how to measure the water level in these very deep artesian bores. The water level sits at around 300m below ground, but we would only need to measure around 10m (max) fluctuations. It will be a permanent fixture and needs to be a continuous level gauge.

Previously we have used Druck level transmitters, but due to the arduous water flow conditions, the probe cable has deteriorated and has resulted in failure of the probe.

A bubbler system has been suggested because of its simplicity and ruggedness, but I think this may be difficult to implement at this depth.

I was looking at ultrasonic/radar devices, but these seem to have only a very limited range.

Does anyone have any further ideas?

Thanks in advance!

 

[itsmoked]

Okay for starters read this tome which I believe just happens to be the longest thread on the site @ +250:

thread240-58310

Is there something obscuring the bore like a pipe?

Is this a water well or a monitoring hole?

Do you know if the hole is straight i.e. could a dropped pebble devoid of all aerodynamics hit the bottom without hitting a wall?

How dynamic must your readings be? (another words would once a minute work?)

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

Keith,

I was looking for that one. Shall we start all over again? Sacrificing little animals behind well and all that?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Hi Gunnar.

Don't forget the multiple six packs!

I think it will be interesting to see the answers to my questions as that could substantially change everything, as compared to alternety's situation.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[joy56]

Thanks for your replies.

I had a read of that epic thread! Certainly some interesting ideas. It also answered some of my questions about the pressure down the bore and other things, so thanks very much for pointing me in that direction =)

To answer your questions:

Looking at the diagrams again, there are rods etc in the middle of the bore above where the pressure transducer used to be.

It is a water well - water is pumped up from about 240m underground.

It is a straight bore, but as I was saying above, there are pipes and things that may get in the way...

The readings I would like to be as often as possible, although every minute would probably be acceptable.

Thanks again.

 

[itsmoked]

So you want to control the pumping with the level?

A radio guy could probably hand craft a radar unit that could reach the bottom and back for a round trip time-of-flight depth measurement. The metal stuff at the bottom will act to mar the crisp return, which will reduce the accuracy some. Too much? I don't know.

Otherwise I would just go for one of those higher end down-hole-pressure transducers. I'd use a 4-20mA sensor. Anything you use will need to be serviced and repaired occasionally, a stainless steel pressure transducer should last many, many, years.

Alternatively an EE could possibly make a sonic system. A loud sharp sound which is reflected back from the water surface, again time-of-flight.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[joy56]

Thanks Keith,

I'm not so much wanting to control the pumping with the level, as just to monitor the level for regulatory requirements.

I do like the idea of the radar or sonic system - the only problem I had was that the maximum range measured is generally only tens of metres, not hundreds. If I could find such a system, it would be much less complicated and have lower maintenance costs.

Cabled pressure transducers have been used in the past, but with the cables failing twice already, I'm a little apprehensive about trying them again... =P

 

[itsmoked]

Where are you? It would be fun to check some ideas.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[danw2]

Your best commercial bet would be laser. It mounts from the top, the beam is narrow and it can shoot long distances.

Optech's Watchman model shoots 250m (lower the head 50m down the well)

http://www.optech.ca/i3d-lvlmonitors.htm

Good luck (sarcasm mode on) with ultrasonics. In effect, a well casing is a very long stilling well.

The warning in the Siemens ultrasonic manual reads,

"Note: When using a stilling well, make sure there is no build-up, welds, couplings, or other debris on the inside of the well wall. This can affect the reliability of level
measurement."

Each weld bead or coupling onnection provides its own 'false" echo reflection.

And as Joy56 has pointed out, commercial ultrasonic units are for shots 10s of meter in distance, not hundreds.

Siemens just introduced a very long shot radar, the LR460, but I lost the email with the details.

Dan

 

[joy56]

Thanks so much Dan for your ideas. I've had a look at Optech's laser specs, and it seems to solve the situation perfectly. But I just received a quote from them - $9000 (!) The LR460 only has a range up to 100m, but I will look into installation location possibilities which would make this a viable option.

There's always some tradeoff with any solution whether it be cost, installation or maintenance etc - so I think I'll just have to weigh it all up!

Keith - I'm in Australia...

Thank you all again.

 

[danw2]

A note on the radar unit.

On tanks, Siemens radar is very fussy about having its 'shield' extend below the stand-off or nozzle so that the radiating part of the antenna extends inside the tank, not up above the tank, raised up inside a nozzle.

I honestly don't know how a radar works in a stilling well. Short shot ultrasonics can generally be made to work.

But it would be advisable to ascertain why a radar would work for a 250m shot down a long tube if that same radar doesn't like its shield inside of a nozzle that is thte equivalent diameter of your bore hole.

Dan

 

[itsmoked]

I have a real problem with a laser... First water is not the best perpendicular reflector. Only a tiny, tiny reflection will return. Furthermore if the water surface has ripples on it due to say.. vibration from the pump the laser reflection would likely be non-perpendicular and hence be absorbed rapidly by the bore wall. But most importantly I bet that bore is as crooked as a snake, and hence no line-of-sight exists!

I would suggest something like a sub-woofer that puts out one big thump then waits the [300m x 2]/502m/s = 1.1952seconds for a return. Digitally process the the reflections dump out the depth. Easy! <snicker>

Dang joy56; Australia and California are kinda far apart..

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[joy56]

Yeah I agree with you about the laser Keith, it would be difficult on the water surface - it was suggested to me that you would put a floating reflector on the bottom. I'm not so sure about that, and with the high cost I don't think it is a viable option.

I'd love to see that subwoofer in operation =D

Thanks again Keith and Dan, your ideas have been most useful, and I really appreciate your help! Should have enough information now =)

Cheers guys.