In Darcy's law, discharge is influenced by which factors?

• A. All three factors influence discharge: hydraulic conductivity, cross-sectional area, and hydraulic gradient
• B. Hydraulic conductivity
• C. Cross-sectional area
• D. Hydraulic gradient

Answer: (A)

In Darcy's law, discharge through a porous medium is determined by three quantities: the hydraulic conductivity of the material (how easily water moves through it), the cross-sectional area available for flow, and the hydraulic gradient driving the flow along the path. The law is written as Q = -K A (dh/dl), so the magnitude of discharge grows with higher conductivity, a larger flow area, and a steeper gradient.

Hydraulic conductivity reflects the material’s properties and pore connectivity—more permeable soils or rocks allow water to pass more readily, so increasing K increases Q for fixed area and gradient. The cross-sectional area represents how much pore space is in the flow path; a larger area provides more pathways for water, boosting discharge. The hydraulic gradient is the driving force: a steeper gradient means water has a stronger push, increasing Q for given K and A.

If any one of these factors is very small or zero, discharge becomes limited or stops, underscoring why all three collectively determine how much water moves.