Groundwater Well TDH

[Sowega]

I've been given a project to design a groundwater well with adjacent elevated tank. This will be my first so I have a few questions. Would the static head be the difference in the aquifer to the overflow of the elevated tank? Also, how do I figure what size the well should be? The tank will be a 300,000 gallon tank and the well needs to produce 1000 gpm.
Thanks

 

[cvg]

pump test the well and then you will know how much the well can produce

 

[bimr]

You need to contact a local water well driller who is knowledgable about the water conditions.

 

[Artisi]

From what you have posted I would suggest that you employ someone capable of such an undertaking as the detail you have given / asked is meaningless. A lot more detailed information is necessary to even start thinking about the problem.

The first thing that is needed is to understand the ground conditions,ie, the depth to the aquifer, the permeabilty of the water bearing deposit, and the likely draw-down at the yield you need etc etc.

Once this is established you can then decide on the well diameter, screen length and setting which is a function of the above information - once this information is know you can then move onto other things which will influence the static head for the pumping conditions.

Of course all of the above is the theory and the only way to really establish good solid data is to analyse any other well /s within the same area or install a test well and undertake a controlled pumping test.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[fel3]

In addition to the groundwater side of things that the others have mentioned, you need to consider that the water level in the tank will also vary and this will affect pump operation. Depending on how tall the tank is, this may or may not matter too much.

First, you need to figure out how the tank will operate in the system. For example, most of the tanks I have designed have included three storage components: daily operational storage, fire flow storage, and emergency storage. Assume they are layered this way from the top down. Thus, most of the time, the tank will operate in the upper zone, sometimes into the middle zone, and rarely into the lower zone. However, not all tanks are designed to operate this way. One tank I did was all fire storage and water quality was a bigger issue than hydraulics. If your tank is, say, all operational storage, then the water level could vary from near the top to near the bottom.

In the end, there are typically four water levels that define the operating envelope for a water tank: [1] overflow plus a little for the weir height at your maximum inflow, [2] normal high water level (this may be 6" to 12" below the overflow), [3] normal low water (this depends greatly on what the tank's function is), and [4] absolute low water (i.e. the elevation of your outlet).

Sometimes you can get away with only considering a high and a low water level and other times you may need to check one or two more. My normal approach is to design the pump to handle conditions [2] and [3] around the best efficiency point of the pump, then verify that the pump is OK at [1] and [4]. With software, it's easy to check all conditions.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[bimr]

The static head is the difference between the well pumping level and the maximum water level in the water tower. Drawdown is the drop in level of water between the static groundwater level and the pumping
level.