Advanced Waterworks Mathematics, 2019a

pump tests are performed to determine if the underlying aquifer can supply enough water.
Continuous pumping for an extended period is usually performed and the yield is calculated
based on the amount of water extracted. Well yields are typically measured in the field with a
flow meter.
Drawdown
In order to understand the term drawdown, you must also understand static water level and
pumping water level. The static water level is defined as the distance between the ground
surface and the water level when the well is not operating. The pumping level is defined as the
distance between the ground surface and the water level when a well is pumping. Therefore,
the pumping water level is always deeper than the static water level. The difference between
these two levels is the drawdown. Depending on the aquifer, static water levels can be 20 feet
below ground surface (bgs) or several hundred feet bgs.
Drawdown = Pumping Water Level - Static Water Level
Figure 9.2 40
The diagram above shows a well casing penetrating into the ground, the relationship between
static and pumping water levels, and the drawdown.
40
Image by College of the Canyons Water Technology faculty is licensed under CC BY 4.0
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