Groundwater hydraulics: The basic equation used to determine the average velocity of groundwater flow (m/day) in a porous medium is known as:

Introduction / Context:
Calculating groundwater flow through porous media under laminar conditions relies on a linear relationship between specific discharge and hydraulic gradient. This foundational relationship underlies aquifer tests and flow-net analyses.

Given Data / Assumptions:

• Laminar flow through saturated porous media.
• Hydraulic conductivity K is constant over the path considered.
• Hydraulic gradient i is known (head drop per length).

Concept / Approach:
Darcy’s law states that the specific discharge q (also called Darcy velocity) equals K * i. The seepage (pore) velocity v is q / n_e, where n_e is effective porosity. For engineering estimates, velocity in m/day is commonly reported using these relations.

Step-by-Step Solution:
Use q = K * i (Darcy’s law).If pore velocity is needed: v = q / n_e.These give groundwater velocities in consistent units (e.g., m/day) given K and i (and n_e if required).

Verification / Alternative check:
Field tests (pumping tests) infer K; flow nets and slug tests also use Darcy’s relationship to interpret velocities and fluxes.

Why Other Options Are Wrong:
Meinzer/Slichter/Hazen are associated with empirical relationships for permeability or well hydraulics; Darcy’s formula is the fundamental velocity–gradient law.

Common Pitfalls:
Confusing specific discharge with pore velocity; neglecting porosity correction when estimating actual water particle speeds.

Final Answer:
Darcy’s formula.