calculate drop in elevation by using water flow

This is an ill-defined problem. Lucidity is needed here if you want an answer.

Off-the-Cuff though the answer should be, sort of, yes

I thank all for their answers and am sure they are all right. I will try to get better information. I was using the best I had, not sure about much of it . Impossible to stop the flow and measure pressure. The source is comletely in accessible in an abandoned coal mine. Most of the men who worked on it are all dead and gone. I would guess and it is just a guess the drop would be at least 1 inch to one and a half inches per foot. Can ya'll roughly figure it for a distance of 2000, to 6,000 feet from the discharge in one thousand foot incrments. It is an intersting question though isn't it?

I tend to disagree with the first response, flow by itself cannot tell you the "fall" as you do not know the flow resistance it has passed through to get to that point. (Free flowing through a polished SS pipe versus struggling through a gravel filter)

You could get some indication of the head/fall by completely obstructing the flow and measuring the pressure that is developed (in stable condition) provided there is no filling reservoir behind the rock face.

If you could stop the flow long enough to measure the static pressure, you could easily calculate the elevation of the water surface. As it is, there are too many unknowns and too little data.

You can determine a minimum elevation by neglecting friction in the pipe and determining the pressure required to force 7.6 cubic feet per second through a twelve inch opening. Then do a series of calculations incorporating frictional effects to determine a likely pipe length. This will enable you to make an educated guess, but like any guess, it may be completely wrong.

The source may be inaccessible, but somewhere there is probably some kind of construction record. The best solution in this case might be to find somebody who knows where that record is, and ask them.

Bubba makes the case clear, there are quite a few unknown factors in this. More investigation is warranted here. The flow gives you one small piece of the complete puzzle.

If you can get the pressure at the top of the mountain or wherever the reservoir is located and using a few assumptions you can use Bernoullis equation to give you the height.

h = Δp/ρg + v²/2g

oops i forgot the friction factor.

h = Δp/ρg + v²/2g + h_f

where, h_f= f*L/D*v²/2g

Shank is partially correct. The bigger of the unanswered questions is what is it flowing through (the friction). Does this 12" pipe go the entire way? A map could get you close to the length with the source and the outlet being known.

I have measured elevation by measuring static pressure with a pressure gauge. It works pretty well. You must assure that there are no other pressure sources, or active drains along the elevation route. I checked my work using Google Earth elevarion data. The two measurements were pretty close. I have also used a sensitive barometer to measure differences in elevation.

If you can get access to both ends, you can use a GPS. They give not only longitude/latitude but also elevation above sea level. Not knowing driction will still be a problem if you want to calculate length from flow data but, it the pipe is straight, the GPS data for both ends will give you the length. GPS is accurate within about 10 - 30ft, so this won't work well for short pipelines. Military GPS is accurate within 3-6 ft so if you anyone in the Army, maybe you can borrow one.

I would try to get a column of water set up. Water will seek its own level. If the tube is flexible, just keep raising it until flow stops. You don't have to get too fancy for this method.

The real answer to your question is no. From the information you have you can not estimate the hydraulic head of the flow. It could even be an artesian flow - a flow having a positive pressure but a negative head.

If you can make a intelligent guess as to the pipe length then you could estimate the static head based on the flow.

If you can access the pipe and choke the flow you could use the differential flow rates to estimate the static pressure, or if you can stop the flow you can measure the static pressure or the static head in a stand pipe.

Best wishes,

Mr. Gee

In addition to the other unknown factors here, I am curious as to this: if the 12" pipe is inaccessible, how in the world did it get there? As mentioned, surely there must be installation records somewhere. A 12" pipe is too big for this to have been a seat-of-the-pants project I would think.

Another alternative, if there is actually a pipe at the location and also presuming as someone else has said the source is not "artesian" in nature.

Get a much smaller diameter flexible pipe and insert it up through the water flow until it breaks through into air, drain that small pipe till empty, then bring it back till water begins to fill it. Measure static pressure and divide by necessary density to determine "head".

The next step is to then remove the small tube, buy a matched hydro turbine and start your own small electric company.