Ground Water Level: Darcy’s Law and Permeability

Question 1

What is Darcy’s Law?

Answer 1

Darcy’s Law describes the flow of water through porous material:

𝑞𝑣 = 𝑘 × 𝐴 × Δ𝐻/𝐿

Where:

𝑞𝑣 = Volume flow rate (m³/s)
𝑘 = Permeability coefficient (m/s)
𝐴 = Cross-sectional area (m²)
Δ𝐻 = Hydraulic head difference (m)
𝐿 = Flow path length (m)

Question 2

How is permeability (k) determined?

Answer 2

By laboratory testing a soil sample under controlled flow conditions.

Question 3

What is the typical permeability coefficient (k) for different soil types?

Answer 3

Soil Type Permeability (m/s)

Gravel 10⁻²
Coarse Sand 10⁻² − 10⁻³
Medium-Fine Sand 10⁻³ − 10⁻⁴
Fine Sand 10⁻⁴ − 10⁻⁵
Sand + Clay 10⁻⁵ − 10⁻⁶
Clay 10⁻⁹ − 10⁻¹¹
Peat 10⁻⁷ − 10⁻⁹