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Hydraulic Head Of Water Well


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#1 jknight291

jknight291

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Posted 22 April 2014 - 08:04 AM

I am trying trying to determine the hydraulic head of a water well in order to use that information in a simulation of our facility's water well distribution. I have all information such as the ground elevation of the well head, the depth to water, and pressure head of the water based on the attached drawing. My issue is when the depth to water height is greater than my ground elevation of the well head. For instance, for a particular well head, documentation indicates that ground elevation is 16ft MSL, but for that particular well, static water level is 98 ft below ground. So my hydraulic head (according to the attachment) would be ht = e - dtw = 16ft - 98ft = -82ft which naturally doesn't make a lot of sense.

 

I know the solution to this is fairly basic, but I have been wracking my brain for days and I'm just saurated at this point. Does any one have any suggestions as to how I can determine the hydraulic head?

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#2 Art Montemayor

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Posted 22 April 2014 - 09:17 AM

In the past I’ve drilled deepwells in order to supply well water to my process plants and quite frankly, I’m perplexed by what you describe and your calculations.  I like your diagram because it depicts what I believe you have before you as a water well source.

 

If you are proposing to use your drilled well as a source for water distribution above-grade, then you should know and do the following:

 

You have to establish your dynamic water well level below grade.  You do this after you drill the well and you test the source with a test pump.  Your drilling contractor normally can supply this capability.  You have to establish the dynamic water level – which is the level that the aquifer establishes while you are pumping out your design rate of water - because all aquifers will drop in level when they are subjected to a water extraction rate.  The amount of level that the well drops depends on the rate of extraction, the type of formation your aquifer is in, the perforations in your well casing, the depth of the well, and the time of year (if your aquifer is fed from snow melt or other varying sources).

 

The depth that is established by the dynamic water level (at the design flow rate) determines how deep you must place your well pump.  The difference between your well pump suction port and the dynamic level is the net “head” that is of importance to the pump – and to you – because it must satisfy the pump’s NPSH requirement to pump the flow rate that you require.  That is basically the important points you must know when dealing with a water well.

 

The other “data” – sea level datum, elevation head, etc., etc. – are of no importance to the deep well water pump or to the design of the pumping system.  What essentially is of prime importance is that the aquifer have the ability to supply the required flow rate of water to the pump while maintaining itself fairly static and constantly ABOVE the suction port of your well pump.  The pump will take this water source, add mechanical energy to it and pump out the water above your grade level at the pressure it is designed to produce in accordance with its performance curve.

 

Have I explained the application successfully and addressed your concerns?






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