Which statement correctly describes hydraulic conductivity and its role in Darcy's law?

• A. Hydraulic conductivity is the depth to the water table
• B. Hydraulic conductivity is the rate of precipitation infiltration
• C. Hydraulic conductivity is a measure of a medium's ability to transmit water; in Darcy's law q = -K ∙ i
• D. Hydraulic conductivity is the chemical diffusion coefficient

Answer: (C)

Hydraulic conductivity is a measure of how easily water can move through a porous medium. In Darcy’s law, the flow rate per unit area, q, is proportional to the hydraulic gradient i, with the constant of proportionality K, the hydraulic conductivity: q = -K i. This means that for a given gradient, a medium with higher K transmits water more readily. The negative sign simply indicates flow from higher hydraulic head to lower head. K depends on both the fluid’s properties (like viscosity) and the medium’s characteristics (pore size, connectivity, tortuosity). This concept is specifically about water transmission through a material under a gradient; the other ideas describe different processes—depth to the water table, rainfall infiltration rate, or diffusion of chemicals—not the ease of water movement under a gradient.