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How It Works
Darcy's Law (Q = k × i × A) describes fluid flow through porous media like soil or rock. The flow rate is proportional to the hydraulic conductivity of the material, the hydraulic gradient driving the flow, and the cross-sectional area. It is the foundation of groundwater hydrology and geotechnical engineering.
Example Problem
A sandy aquifer has k = 0.001 m/s, a hydraulic gradient of 0.05, and a cross-sectional area of 10 m². What is the groundwater flow rate?
- Q = k × i × A
- Q = 0.001 × 0.05 × 10 = 0.0005 m³/s (0.5 L/s)
Frequently Asked Questions
What is Darcy's Law used for?
It predicts the volumetric flow rate of groundwater through soil, rock, or engineered filter media. Engineers use it for well design, dewatering calculations, and contaminant transport modeling.
What is hydraulic conductivity?
Hydraulic conductivity (k) measures how easily water moves through a porous material, in m/s. Gravel may have k of 0.01–1 m/s, sand 10-4–10-2 m/s, and clay below 10-8 m/s.
What is the difference between Darcy velocity and seepage velocity?
Darcy velocity (v = k × i) is the apparent velocity over the full cross-section. The actual seepage velocity through pores is higher: vs = v/n, where n is the porosity. This matters for contaminant travel time estimates.
Related Calculators
- French Drain Design Calculator — applies Darcy's Law to residential drainage design.
- Fluid Pressure Calculator — calculate hydrostatic pressure from density and depth.
- Hydraulic Radius Calculator — compute channel flow geometry parameters.
- Permeameter Calculator — measure hydraulic conductivity of soil samples in the lab.
- Length Converter — convert between meters, feet, and other length units for head calculations.