water well depth

Yes, a clamp-on ammeter will give you an approximate answer. Just clamp onto one of the AC legs. If you have a pressure tank, this won't be accurate, as the head will increase as the tank pressurizes.

My well guy uses a sonar gauge. Fairly low-tech, actually; it used a bullhorn/PA horn driver, and sent out a low frequency "thump", then measured time until the echo returned. Requires lifting the well cap, though.

--Gene

If your well is like mine, it pumps into a pressure tank---the pressure in which varies from 40 to about 75 PSI as the tank fills. That change in head pressure is equivalent to a change in water level of about 60 feet. To get rid of that changing addition to the energy needed to lift the water, you have to make your measurement at the same point in the tank filling cycle.

If this is an irrigation well, your head pressure will vary with the number and type of sprinklers.

What type of resolution do you need? 825 feet is a pretty deep well, and a 1% power sensor may be difficult to build. This is especially true in light of possible line voltage fluctuations.

When you pump a lot of water, you should expect the water depth in the well to go down unless the aquifer is very porous.

Mark Borgerson

With most pumps the throughput varies with the presure, so you also have to measure the flow. The heigth will be power/flow, corrected for the (changing )efficiency of the pump.

Wim

Right, the responders to this question know the complexity. Yes I have a pressure tank (rubber bladder inside the tank). It would seem that a ratio between an easily installed electronically readable (after all it is in the well house) pressure gauge and some power to pump current measure would give a relative depth. My water level when drilled to

825 feet filled to about 350 feet. So the force required to lift water was from 350 feet. I really cannot insert anything into the well, without messing up the pump.

What I would like is a passive method (from the well top) to get the relative depth. The idea being if I know that at the start of spring the depth is x, what is the depth the rest of the year? I suspect this is a general interest question and some analog guy probably has some method of determining it. I am not that guy.

Regards ~Steve

Hi Steve,

Ok, since I am an analog guy I now feel prodded for an idea. We don't have a well, else I probably would have tried something already. Quite frankly I don't know much about wells either. But the first step I'd try is echo, as one of the other respondents had mentioned.

This doesn't have to be a huge trumpet requiring lots of space. If you want to experiment try a small speaker, send a short burst from a function generator and look for echoes on a scope. Play with the frequency to see what gives the best echo in your situation. You may need a preamp that is overdrive proof (diodes etc.) and a filter but that shouldn't be a big deal. The goal is to isolate the echo so well that detection is sufficiently secure.

If that works and you want to build something more permanent post again and we can share more ideas. Basically then you'd have to find a speaker plus maybe a microphone that won't corrode easily and equip your receive chain with a 'range gate'. That is a gate which blocks echoes from unreasonable ranges, for example for the first couple hundred feet and then past the bottom of your well, to prevent multiple path returns from being detected.

All this is very similar to ultrasound equipment.

Regards, Joerg

When the pump is not running, does the water in the line recede to the level in the well, or does the line stay primed?

Could you simply time how long it takes for the water to reach the tank when the pump is engaged? If it takes the pump N seconds to deliver water to the surface, then referencing N against a scale (either calculated or benchmarked at different levels) would tell the rough depth.

If the water in the line drops when the pump is off, and if the air in the line is easily evacuated by the pump when it engages, then the tank bladder would not apply any back-pressure until the water reaches the tank. So, the level of the tank would not be a factor.

From the proposed sonar solutions, it sounds like the line recedes to water level when idle, so maybe this scheme could work?

If you have a means of placing a virtual electrode at the water surface, you might be able to measure the ohmic resistance from there to the pump, and thence the ohmic resistance from the pump to the wellhead. To do this you need a conductor down to the water surface, which might be a steel casing. I would assume from the pump up is a plastic pipe, which can insulate from the surrounding water. Of course the water conductance depends on the impurities, which may or may not be constant.

If you can get an ohmic reading between the casing at the surface, and the returning column of water, and my insulation assumptions are right, that should be some sort of calibratable value. Maybe.

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One way might be to drop a water-pressure gauge to the bottom of the well. The weight of the column of water on top of the gauge can be used to calculate the height of the column.

CBFalc> > wrote:

Or if the pump is located at the top of the well, mount a pressure sensor to measure the suction. This would be inverse proportional to the water level.

Tom

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I don't think you can put the pump there with an 825' well with water

300 odd feet down. The pump is holding up 10 atmospheres or so (I assume the pump floats on the water, rather than pumps from the bottom all the time). A tough pressure gauge down there might help. Otherwise an automated stone dropper and ear.

Paul Burke

His well is 825 feet deep. You cannot suck water up to more than the airpressure's worth of water column, which is 10 meters or 33 feet. So there is no pump at the top.....

Meindert

Typical installation of submersible pumps includes a checkvalve at the pump. The entire feed line from the pump to the tank remains full of water and pressurized at the tank pressure. As soon as the pump starts, the water begins to flow immediately. There is to time lag to measure.

-Robert Scott Ypsilanti, Michigan (Reply through this forum, not by direct e-mail to me, as automatic reply address is fake.)

While I suspect there is SOME limit, it is quite possible to have the pump at the top of a well that is deeper than 33ft. Check out "jet pumps" for details. Basically, a jet pump uses two lines to pump the water in a loop, at the bottom of the loop, is a venturi. The "low pressure in the venturi sucks more water into the system. Neat trick. I used one of these for years.

Suction pumps fail slightly before the 800 odd foot depth specified. I think the OP specified no in-well sensors were available.

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While I agree that the OP said no "in well" sensors were allowed, I just thought of another clever way to measure the column of water.

Consider a tube running down to near the bottom of the well, with the bottom of the tube open to the water. Now, slowly introduce compressed air into the hose. The air will displace the water until the air starts bubbling out of the bottom of the hose. The air pressure (PSI) will then become constant. That terminal air pressure will correlate to the depth of the water column that was forced out. No? (i.e. it easy to blow bubbles in your glass of water, but harder to blow bubbles at the bottom of an 800foot well)

Sure, you'd have to make some adjustments for the "weight" of the air, etc, but considering the relative densities of water and air, I suspect these could be ignored.

- jim

CBFalc>

How about something similar to a time-domain reflectometer? You use a solenoid to tap the pipe supporting the pump and listen for echoes. You should get an echo at the point where the water in the well changes the acoustic impedance of the pipe. The speed of sound in steel is about 4500m/second. If you can detect echoes with 250 microsecond resolution, that would give you about 1-meter resolution in depth. The pump itself should give you another (and stronger). That echo could be used for auto calibration if you know the length of pipe to the pump.

Detecting the echo might be an interesting DSP project--you could capture a representation of the outgoing pulse, and use auto-correlation to detect the return. A bit of research on sonar and ultrasound systems seems in order.

Mark Borgerson

Bubblers are a well-established depth measurement technology that has been used for years. The trouble with a retrofit situation is that it is hard to get the darned tube down there, past the "pit-less adapter" (any well-buffs out there know that term?)

Personally, I like the echo method. If it is done right, it can siphon power from the AC line during pump operations, and then used the stored energy (maybe in a supercap?) when the pump turns off (so that things are quiet). The results could be sent back along the AC line using one of the low-bandwidth data-over-power-line technologies. Gee, if it weren't so darned cold here in Michigan I would be tempted to go out and try some experiments on my well right now :-)

-Robert Scott Ypsilanti, Michigan (Reply through this forum, not by direct e-mail to me, as automatic reply address is fake.)

Classic oilfield technique. Extremely precise measurments can be made if you use helium instead of air/nitrogen and if you carefully compensate for the temperature and density of the gas.

Probably not practical for a 800 foot water well without the capillary tube.

I have used a cheap method on my well. I lower a plumb bob on a cord and listen for the point where I can spash it on the surface of the water. Then I mark the point on the cord and haul it up and measure the length of cord from the plumb bob to the mark on the cord. Very low tech. Also it doesn't address the dynamic issue of level depression during pumping. But it does tell you if the overall static water table is dropping.

-Robert Scott Ypsilanti, Michigan (Reply through this forum, not by direct e-mail to me, as automatic reply address is fake.)