# What is the difference between the Hydraulic diffusion equation and the Richards equation in groundwater dynamics?

What is the difference between the Hydraulic diffusion equation and the Richards equation in groundwater dynamics? I want also to understand the difference between the different storage coefficients (Ss, S,..).

Both are differential equations:

Diffusivity equation: $$\ Ss. ∂h/ ∂t = −∇ ·(− K \nabla h) − G$$.(for Incompressible liquid)(the flux (q), source terms (G), the specific storage (Ss), hydraulic head (h)) (source)

Richards equation (headed based form (there two other forms of this equation)): $$C(h) . ∂h/∂t = ∇ · K(h)∇H$$ (specific moisture capacity C(h), (H) total hydraulic head, h is the matric head) (source)

Aren't they supposed to describe unsaturated flow ???

• can you write those equations in your question so we can avoid searching for it ? – gansub May 16 '17 at 10:45
• Both are differential equations: Diffusivity equation: Ss. ∂h/ ∂t = −∇ · (−K∇h) − G.(for Incompressible liquid)(the flux (q), source terms (G), the specific storage (Ss), hydraulic head (h)) (source:en.wikipedia.org/wiki/Groundwater_flow_equation) Richards equation (headed based form (there two other forms of this equation)): C(h) . ∂h/∂t = ∇ · K(h)∇H (specific moisture capacity C(h), (H) total hydraulic head, h is the matric head) (source: en.wikipedia.org/wiki/Richards_equation) Aren't they supposed to describe unsaturated flow ??? – Rabah Akrour May 16 '17 at 11:16
• can you include them in the question using MathJax ? – gansub May 16 '17 at 12:06
• Voila, easy to use ! – Rabah Akrour May 16 '17 at 12:19