Which variables are used in Darcy's law to estimate groundwater flow in porous media?

• A. Hydraulic conductivity, cross-sectional area, and hydraulic gradient
• B. Temperature, salinity, and porosity
• C. Storage change, precipitation, and evaporation
• D. Hydraulic conductivity only

Answer: (A)

Darcy's law links groundwater flow to three factors: how easily water moves through the medium (hydraulic conductivity, K), the cross-sectional area available for flow (A), and the slope of the hydraulic head that drives the flow (the hydraulic gradient, i = Δh/Δℓ). The discharge rate is proportional to K, A, and the gradient, written as Q = -K A i. This is why the best choice includes hydraulic conductivity, cross-sectional area, and hydraulic gradient.

Temperature and salinity can influence the fluid's viscosity and density—affecting K—but they are not separate variables in the standard law. Porosity tells us how much water the pore space can hold (storage), not the instantaneous flow rate through a medium. Storage change, precipitation, and evaporation describe recharge or discharge processes, not the direct relationship between flow and gradient that Darcy's law expresses.