# Calculate a purge or flow rate

#### sdm1980

##### New Member
Hi everyone, somewhat new to using excel.
So here's the problem I am having

I am trying to calculate a flow/purge rate from water being purged from a well

10:43am static water level (SWL) was 7.82m known purge rate of 8LPM (litres per minute)
10:46am SWL was 7.87m purge rate ?
10:49am SWL was at 7.9m, purge rate ?
10:52am SWL was at 7.925m, purge rate ?
10:55am SWL was at 7.962m, purge rate ?
10:59am SWL was at 8m, purge rate ?

What I would like to do is have a formula that automatically calculates the change in purge rate. Any information would be greatly appreciated

### Excel Facts

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If water is being purged from the well, surely the level should be decreasing

There is inadequate known information to create a formula.

the level is top of casing to water level, so picture if you were standing over a sump/pool/etc. and taking a measurement from there. as you take more water out the measurement of the water level will increase.

well parameters are as follows
well diameter: 2 inch diameter
volume/meter: 2.024 L
total depth of well: 26.64
static water level before purge starts: 7.59m
H2O Length: 19.05m
well volume: 38.5572L

Don't you need to know how much water is flowing into the well? And doesn't that depend on the height of the water column?

Or does the purge pump's volume just vary inversely with SWL?

Or ...??

Last edited:
If I understand this correctly then the formula structure should be

=((PI*(Raduius^2)*(current level - previous level)*1000)/((current time stamp - previous time stamp)*1440)

The multiplier of 1000 converts the initial calculation from cubic metres to litres. The multiplier of 1440 is to convert the decimal value of the time difference to minutes.

With times in column A and water levels in column B

=((PI()*(0.0254^2)*(B3-B2))*1000)/((A3-A2)*1440)

Should return the rate of litres per minute.

shg
You're my hero if that's correct.

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