The storage coefficient and transmissivity are two important parameters calculated by using which equation?

• A. Theis equation
• B. Darcy's law
• C. Dupuit equation
• D. Seawater intrusion equation

Answer: (A)

When interpreting pumping-test responses in a confined aquifer, the key relationship is provided by the Theis equation. It describes how drawdown near a pumped well changes over time due to transient radial flow and ties that response directly to two properties: transmissivity and storage coefficient. Transmissivity, T, reflects how easily water can move through the aquifer (K times thickness), while the storage coefficient, S, represents how much water is released from storage as pressure and concentration change propagate. The Theis solution gives drawdown s as a function of pumping rate Q, time t, distance r from the well, and the aquifer parameters T and S (through the well function W(u) with u = r^2 S /(4 T t)). This makes it the appropriate equation to determine both T and S from pumping-test data.

Darcy's law describes the instantaneous relationship between flow and hydraulic gradient but doesn’t by itself capture the time-dependent, well-centered drawdown needed to estimate storage and transmissivity. The Dupuit equation is a simplification used for certain unconfined conditions and steady or quasi-steady flow, not the transient confined-aquifer pumping scenario that yields T and S. The seawater intrusion equation is not a standard groundwater-flow solution for pumping tests and doesn’t provide the required link between drawdown, time, and the aquifer properties.

So, the Theis equation is the best fit because it uniquely connects the time-dependent drawdown around a pumped well to the two critical aquifer properties, enabling their estimation from pumping data.