The amount of water that can be pumped is limited by the drawdown produced.
Typically, drawdown also increases with the length of time that the pumping continues.
The components of observed drawdown in a pumping well were first described by Jacob (1947), and the test was refined independently by Hantush (1964) and Bierschenk (1963) as consisting of two related components, where s is drawdown (units of length e.g., m),
is the aquifer loss coefficient (which increases with time — as predicted by the Theis solution) and
To quantify this it is necessary to pump the well at several different flow rates (commonly called steps).
Rorabaugh (1953) added to this analysis by making the exponent an arbitrary power (usually between 1.5 and 3.5).
To analyze this equation, both sides are divided by the discharge rate (
on the left side, which is commonly referred to as specific drawdown.
) since the beginning of each step of the test (since drawdown will continue to increase with time) versus pumping rate should produce a straight line.
Specific capacity is a quantity that which a water well can produce per unit of drawdown.
Due to non-linear well losses the specific capacity will decrease with higher pumping rates.